Re: [DISCUSS] scalability limits in the coordinator

[Onur Karaman <ok...@linkedin.com.INVALID>]

I made a PR with a tweak to Jun's/Becket's proposal:
https://github.com/apache/kafka/pull/1484

It just tweaks the fetch behavior specifically for replicas fetching from
the __consumer_offsets topic when the fetcher's "replica.fetch.max.bytes"
is less than the __consumer_offset leader's "message.max.bytes" to take the
max of the two.

I'm honestly not that happy with this solution, as I'd rather not change
the "replica.fetch.max.bytes" config from being a limit to a
recommendation. I'd definitely be happy to hear other alternatives!

On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <on...@gmail.com>
wrote:

> Sorry I know next to nothing about Kafka Connect. I didn't understand the
> Kafka Connect / MM idea you brought up. Can you go into more detail?
>
> Otherwise I think our remaining options are:
> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
> __consumer_offsets topic and change the fetch behavior when message size is
> larger than fetch size
> - option 6: support sending the regex over the wire instead of the fully
> expanded topic subscriptions. This should cut down the message size from
> the subscription side. Again this only helps when pattern-based
> subscriptions are done.
>
> minor correction to an earlier comment I made regarding the message size:
> message size ~ sum(s_i + a_i for i in range [1, |C|])
>
> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <ja...@confluent.io>
> wrote:
>
> > Hey Onur,
> >
> > Thanks for the investigation. It seems the conclusion is that the compact
> > format helps, but perhaps not enough to justify adding a new assignment
> > schema? I'm not sure there's much more room for savings unless we change
> > something more fundamental in the assignment approach. We spent some time
> > thinking before about whether we could let the consumers compute their
> > assignment locally from a smaller set of information, but the difficulty
> > (I'm sure you remember) is reaching consensus on topic metadata. Kafka
> > Connect has a similar problem where all the workers need to agree on
> > connector configurations. Since all configs are stored in a single topic
> > partition, the approach we take there is to propagate the offset in the
> > assignment protocol. Not sure if we could do something similar for MM...
> > Anyway, it seems like the best workaround at the moment is Jun's initial
> > suggestion. What do you think?
> >
> > -Jason
> >
> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> > onurkaraman.apache@gmail.com
> > > wrote:
> >
> > > I gave the topic index assignment trick a try against the same
> > environment.
> > > The implementation just changed the assignment serialization and
> > > deserialization logic. It didn't change SyncGroupResponse, meaning it
> > > continues to exclude the subscription from the SyncGroupResponse and
> > > assumes the member has kept track of its last subscription.
> > >
> > > Assignment topic indexing with compression:
> > > 1 consumer 34346 bytes
> > > 5 consumers 177687 bytes
> > > 10 consumers 331897 bytes
> > > 20 consumers 572467 bytes
> > > 30 consumers 811269 bytes
> > > 40 consumers 1047188 bytes * the tipping point
> > > 50 consumers 1290092 bytes
> > > 60 consumers 1527806 bytes
> > > 70 consumers 1769259 bytes
> > > 80 consumers 2000118 bytes
> > > 90 consumers 2244392 bytes
> > > 100 consumers 2482415 bytes
> > >
> > > Assignment topic indexing without compression:
> > > 1 consumer 211904 bytes
> > > 5 consumers 677184 bytes
> > > 10 consumers 1211154 bytes * the tipping point
> > > 20 consumers 2136196 bytes
> > > 30 consumers 3061238 bytes
> > > 40 consumers 3986280 bytes
> > > 50 consumers 4911322 bytes
> > > 60 consumers 5836284 bytes
> > > 70 consumers 6761246 bytes
> > > 80 consumers 7686208 bytes
> > > 90 consumers 8611170 bytes
> > > 100 consumers 9536132 bytes
> > >
> > > Assignment topic indexing seems to reduce the size by 500KB without
> > > compression and 80KB with compression. So assignment topic indexing
> makes
> > > some difference in both with and without compression but in our case
> was
> > > not nearly enough.
> > >
> > > This can be explained by the fact that we aren't actually hitting the
> > worst
> > > case scenario of each consumer being assigned a partition from every
> > topic.
> > > The reason is simple: a topic can only fully span all the consumers if
> it
> > > has at least as many partitions as there are consumers. Given that
> there
> > > are 8 partitions per topic and we have 100 consumers, it makes sense
> that
> > > we aren't close to this worse case scenario where topic indexing would
> > make
> > > a bigger difference.
> > >
> > > I tweaked the group leader's assignment code to print out the
> assignments
> > > and found that each consumer was getting either 238 or 239 partitions.
> > Each
> > > of these partitions were from unique topics. So the consumers were
> really
> > > getting partitions from 239 topics instead of the full worst case
> > scenario
> > > of 3000 topics.
> > >
> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <ja...@confluent.io>
> > > wrote:
> > >
> > > > Gwen, Joel:
> > > >
> > > > That's correct. The protocol does allow us to give an assignor its
> own
> > > > assignment schema, but I think this will require a couple internal
> > > changes
> > > > to the consumer to make use of the full generality.
> > > >
> > > > One thing I'm a little uncertain about is whether we should use a
> > > different
> > > > protocol type. For a little context, the group membership protocol
> > allows
> > > > the client to provide a "protocol type" when joining the group to
> > ensure
> > > > that all members have some basic semantic compatibility. For example,
> > the
> > > > consumer uses "consumer" and Kafka Connect uses "connect." Currently
> > all
> > > > assignors using the "consumer" protocol share a common schema for
> > > > representing subscriptions and assignment. This is convenient for
> tools
> > > > (like consumer-groups.sh) since they just need to know how to parse
> the
> > > > "consumer" protocol type without knowing anything about the
> assignors.
> > So
> > > > introducing another schema would break that assumption and we'd need
> > > those
> > > > tools to do assignor-specific parsing. Maybe this is OK?
> Alternatively,
> > > we
> > > > could use a separate protocol type (e.g. "compact-consumer"), but
> that
> > > > seems less than desirable.
> > > >
> > > > Thanks,
> > > > Jason
> > > >
> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <gw...@confluent.io>
> > > wrote:
> > > >
> > > > > ah, right - we can add as many strategies as we want.
> > > > >
> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <jj...@gmail.com>
> > > > wrote:
> > > > >
> > > > > > > Yes it would be a protocol bump.
> > > > > > >
> > > > > >
> > > > > > Sorry - I'm officially confused. I think it may not be required -
> > > since
> > > > > the
> > > > > > more compact format would be associated with a new assignment
> > > strategy
> > > > -
> > > > > > right?
> > > > > >
> > > > > >
> > > > > > > smaller than the plaintext PAL, but the post-compressed binary
> > PAL
> > > is
> > > > > > just
> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW using a
> > > > symbol
> > > > > > > table helps a lot but further compression on that already
> compact
> > > > > format
> > > > > > > would yield only marginal return.
> > > > > > >
> > > > > >
> > > > > > > So basically I feel we could get pretty far with a more compact
> > > field
> > > > > > > format for assignment and if we do that then we would
> potentially
> > > not
> > > > > > even
> > > > > > > want to do any compression.
> > > > > > >
> > > > > >
> > > > > > Also just wanted to add that this compression on the binary PAL
> did
> > > > help
> > > > > > but the compression ratio was obviously not as high as plaintext
> > > > > > compression.
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> gwen@confluent.io
> > >
> > > > > wrote:
> > > > > > >
> > > > > > >> Regarding the change to the assignment field. It would be a
> > > protocol
> > > > > > bump,
> > > > > > >> otherwise consumers will not know how to parse the bytes the
> > > broker
> > > > is
> > > > > > >> returning, right?
> > > > > > >> Or did I misunderstand the suggestion?
> > > > > > >>
> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> > > wangguoz@gmail.com>
> > > > > > >> wrote:
> > > > > > >>
> > > > > > >> > I think for just solving issue 1), Jun's suggestion is
> > > sufficient
> > > > > and
> > > > > > >> > simple. So I'd prefer that approach.
> > > > > > >> >
> > > > > > >> > In addition, Jason's optimization on the assignment field
> > would
> > > be
> > > > > > good
> > > > > > >> for
> > > > > > >> > 2) and 3) as well, and I like that optimization for its
> > > simplicity
> > > > > and
> > > > > > >> no
> > > > > > >> > format change as well. And in the future I'm in favor of
> > > > considering
> > > > > > to
> > > > > > >> > change the in-memory cache format as Jiangjie suggested.
> > > > > > >> >
> > > > > > >> > Guozhang
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> > > > becket.qin@gmail.com>
> > > > > > >> wrote:
> > > > > > >> >
> > > > > > >> > > Hi Jason,
> > > > > > >> > >
> > > > > > >> > > There are a few problems we want to solve here:
> > > > > > >> > > 1. The group metadata is too big to be appended to the
> log.
> > > > > > >> > > 2. Reduce the memory footprint on the broker
> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> > > > > > >> > >
> > > > > > >> > > To solve (1), I like your idea of having separate messages
> > per
> > > > > > member.
> > > > > > >> > The
> > > > > > >> > > proposal (Onur's option 8) is to break metadata into small
> > > > records
> > > > > > in
> > > > > > >> the
> > > > > > >> > > same uncompressed message set so each record is small. I
> > agree
> > > > it
> > > > > > >> would
> > > > > > >> > be
> > > > > > >> > > ideal if we are able to store the metadata separately for
> > each
> > > > > > >> member. I
> > > > > > >> > > was also thinking about storing the metadata into multiple
> > > > > messages,
> > > > > > >> too.
> > > > > > >> > > What concerns me was that having multiple messages seems
> > > > breaking
> > > > > > the
> > > > > > >> > > atomicity. I am not sure how we are going to deal with the
> > > > > potential
> > > > > > >> > > issues. For example, What if group metadata is replicated
> > but
> > > > the
> > > > > > >> member
> > > > > > >> > > metadata is not? It might be fine depending on the
> > > > implementation
> > > > > > >> though,
> > > > > > >> > > but I am not sure.
> > > > > > >> > >
> > > > > > >> > > For (2) we want to store the metadata onto the disk, which
> > is
> > > > what
> > > > > > we
> > > > > > >> > have
> > > > > > >> > > to do anyway. The only question is in what format should
> we
> > > > store
> > > > > > >> them.
> > > > > > >> > >
> > > > > > >> > > To address (3) we want to have the metadata to be
> > compressed,
> > > > > which
> > > > > > is
> > > > > > >> > > contradict to the the above solution of (1).
> > > > > > >> > >
> > > > > > >> > > I think Jun's suggestion is probably still the simplest.
> To
> > > > avoid
> > > > > > >> > changing
> > > > > > >> > > the behavior for consumers, maybe we can do that only for
> > > > > > >> offset_topic,
> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is
> smaller
> > > than
> > > > > the
> > > > > > >> > > message size on the offset topic, we always return at
> least
> > > one
> > > > > full
> > > > > > >> > > message. This should avoid the unexpected problem on the
> > > client
> > > > > side
> > > > > > >> > > because supposedly only tools and brokers will fetch from
> > the
> > > > the
> > > > > > >> > internal
> > > > > > >> > > topics,
> > > > > > >> > >
> > > > > > >> > > As a modification to what you suggested, one solution I
> was
> > > > > thinking
> > > > > > >> was
> > > > > > >> > to
> > > > > > >> > > have multiple messages in a single compressed message.
> That
> > > > means
> > > > > > for
> > > > > > >> > > SyncGroupResponse we still need to read the entire
> > compressed
> > > > > > messages
> > > > > > >> > and
> > > > > > >> > > extract the inner messages, which seems not quite
> different
> > > from
> > > > > > >> having a
> > > > > > >> > > single message containing everything. But let me just put
> it
> > > > here
> > > > > > and
> > > > > > >> see
> > > > > > >> > > if that makes sense.
> > > > > > >> > >
> > > > > > >> > > We can have a map of GroupMetadataKey ->
> > > > GroupMetadataValueOffset.
> > > > > > >> > >
> > > > > > >> > > The GroupMetadataValue is stored in a compressed message.
> > The
> > > > > inner
> > > > > > >> > > messages are the following:
> > > > > > >> > >
> > > > > > >> > > Inner Message 0: Version GroupId Generation
> > > > > > >> > >
> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can
> compress
> > > the
> > > > > > bytes
> > > > > > >> > here)
> > > > > > >> > >
> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> > > > > > >> > > ....
> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> > > > > > >> > >
> > > > > > >> > > The MemberMetadata format is the following:
> > > > > > >> > >   MemberMetadata => Version Generation ClientId Host
> > > > Subscription
> > > > > > >> > > Assignment
> > > > > > >> > >
> > > > > > >> > > So DescribeGroupResponse will just return the entire
> > > compressed
> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return the
> > > > > > corresponding
> > > > > > >> > inner
> > > > > > >> > > message.
> > > > > > >> > >
> > > > > > >> > > Thanks,
> > > > > > >> > >
> > > > > > >> > > Jiangjie (Becket) Qin
> > > > > > >> > >
> > > > > > >> > >
> > > > > > >> > >
> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson <
> > > > > > jason@confluent.io>
> > > > > > >> > > wrote:
> > > > > > >> > >
> > > > > > >> > > > Hey Becket,
> > > > > > >> > > >
> > > > > > >> > > > I like your idea to store only the offset for the group
> > > > metadata
> > > > > > in
> > > > > > >> > > memory.
> > > > > > >> > > > I think it would be safe to keep it in memory for a
> short
> > > time
> > > > > > after
> > > > > > >> > the
> > > > > > >> > > > rebalance completes, but after that, it's only real
> > purpose
> > > is
> > > > > to
> > > > > > >> > answer
> > > > > > >> > > > DescribeGroup requests, so your proposal makes a lot of
> > > sense
> > > > to
> > > > > > me.
> > > > > > >> > > >
> > > > > > >> > > > As for the specific problem with the size of the group
> > > > metadata
> > > > > > >> message
> > > > > > >> > > for
> > > > > > >> > > > the MM case, if we cannot succeed in reducing the size
> of
> > > the
> > > > > > >> > > > subscription/assignment (which I think is still probably
> > the
> > > > > best
> > > > > > >> > > > alternative if it can work), then I think there are some
> > > > options
> > > > > > for
> > > > > > >> > > > changing the message format (option #8 in Onur's initial
> > > > > e-mail).
> > > > > > >> > > > Currently, the key used for storing the group metadata
> is
> > > > this:
> > > > > > >> > > >
> > > > > > >> > > > GroupMetadataKey => Version GroupId
> > > > > > >> > > >
> > > > > > >> > > > And the value is something like this (some details
> > elided):
> > > > > > >> > > >
> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation
> > > > > [MemberMetadata]
> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
> Assignment
> > > > > > >> > > >
> > > > > > >> > > > I don't think we can change the key without a lot of
> pain,
> > > but
> > > > > it
> > > > > > >> seems
> > > > > > >> > > > like we can change the value format. Maybe we can take
> the
> > > > > > >> > > > subscription/assignment payloads out of the value and
> > > > introduce
> > > > > a
> > > > > > >> new
> > > > > > >> > > > "MemberMetadata" message for each member in the group.
> For
> > > > > > example:
> > > > > > >> > > >
> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> > > > > > >> > > >
> > > > > > >> > > > MemberMetadataValue => Version Generation ClientId Host
> > > > > > Subscription
> > > > > > >> > > > Assignment
> > > > > > >> > > >
> > > > > > >> > > > When a new generation is created, we would first write
> the
> > > > group
> > > > > > >> > metadata
> > > > > > >> > > > message which includes the generation and all of the
> > > > memberIds,
> > > > > > and
> > > > > > >> > then
> > > > > > >> > > > we'd write the member metadata messages. To answer the
> > > > > > DescribeGroup
> > > > > > >> > > > request, we'd read the group metadata at the cached
> offset
> > > > and,
> > > > > > >> > depending
> > > > > > >> > > > on the version, all of the following member metadata.
> This
> > > > would
> > > > > > be
> > > > > > >> > more
> > > > > > >> > > > complex to maintain, but it seems doable if it comes to
> > it.
> > > > > > >> > > >
> > > > > > >> > > > Thanks,
> > > > > > >> > > > Jason
> > > > > > >> > > >
> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> > > > > becket.qin@gmail.com
> > > > > > >
> > > > > > >> > > wrote:
> > > > > > >> > > >
> > > > > > >> > > > > It might worth thinking a little further. We have
> > > discussed
> > > > > this
> > > > > > >> > before
> > > > > > >> > > > > that we want to avoid holding all the group metadata
> in
> > > > > memory.
> > > > > > >> > > > >
> > > > > > >> > > > > I am thinking about the following end state:
> > > > > > >> > > > >
> > > > > > >> > > > > 1. Enable compression on the offset topic.
> > > > > > >> > > > > 2. Instead of holding the entire group metadata in
> > memory
> > > on
> > > > > the
> > > > > > >> > > brokers,
> > > > > > >> > > > > each broker only keeps a [group -> Offset] map, the
> > offset
> > > > > > points
> > > > > > >> to
> > > > > > >> > > the
> > > > > > >> > > > > message in the offset topic which holds the latest
> > > metadata
> > > > of
> > > > > > the
> > > > > > >> > > group.
> > > > > > >> > > > > 3. DescribeGroupResponse will read from the offset
> topic
> > > > > > directly
> > > > > > >> > like
> > > > > > >> > > a
> > > > > > >> > > > > normal consumption, except that only exactly one
> message
> > > > will
> > > > > be
> > > > > > >> > > > returned.
> > > > > > >> > > > > 4. SyncGroupResponse will read the message, extract
> the
> > > > > > assignment
> > > > > > >> > part
> > > > > > >> > > > and
> > > > > > >> > > > > send back the partition assignment. We can compress
> the
> > > > > > partition
> > > > > > >> > > > > assignment before sends it out if we want.
> > > > > > >> > > > >
> > > > > > >> > > > > Jiangjie (Becket) Qin
> > > > > > >> > > > >
> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason Gustafson <
> > > > > > >> jason@confluent.io
> > > > > > >> > >
> > > > > > >> > > > > wrote:
> > > > > > >> > > > >
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression)
> basically
> > > do
> > > > > > this?
> > > > > > >> If
> > > > > > >> > > the
> > > > > > >> > > > > > topic
> > > > > > >> > > > > > > is a string and the topic is repeated throughout,
> > > won't
> > > > > > >> > compression
> > > > > > >> > > > > > > basically replace all repeated instances of it
> with
> > an
> > > > > index
> > > > > > >> > > > reference
> > > > > > >> > > > > to
> > > > > > >> > > > > > > the full string?
> > > > > > >> > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > > > Hey James, yeah, that's probably true, but keep in
> > mind
> > > > that
> > > > > > the
> > > > > > >> > > > > > compression happens on the broker side. It would be
> > nice
> > > > to
> > > > > > >> have a
> > > > > > >> > > more
> > > > > > >> > > > > > compact representation so that get some benefit over
> > the
> > > > > wire
> > > > > > as
> > > > > > >> > > well.
> > > > > > >> > > > > This
> > > > > > >> > > > > > seems to be less of a concern here, so the bigger
> > gains
> > > > are
> > > > > > >> > probably
> > > > > > >> > > > from
> > > > > > >> > > > > > reducing the number of partitions that need to be
> > listed
> > > > > > >> > > individually.
> > > > > > >> > > > > >
> > > > > > >> > > > > > -Jason
> > > > > > >> > > > > >
> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur Karaman <
> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> > > > > > >> > > > > > wrote:
> > > > > > >> > > > > >
> > > > > > >> > > > > > > When figuring out these optimizations, it's worth
> > > > keeping
> > > > > in
> > > > > > >> mind
> > > > > > >> > > the
> > > > > > >> > > > > > > improvements when the message is uncompressed vs
> > when
> > > > it's
> > > > > > >> > > > compressed.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > When uncompressed:
> > > > > > >> > > > > > > Fixing the Assignment serialization to instead be
> a
> > > > topic
> > > > > > >> index
> > > > > > >> > > into
> > > > > > >> > > > > the
> > > > > > >> > > > > > > corresponding member's subscription list would
> > usually
> > > > be
> > > > > a
> > > > > > >> good
> > > > > > >> > > > thing.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > I think the proposal is only worse when the topic
> > > names
> > > > > are
> > > > > > >> > small.
> > > > > > >> > > > The
> > > > > > >> > > > > > > Type.STRING we use in our protocol for the
> > > assignment's
> > > > > > >> > > > TOPIC_KEY_NAME
> > > > > > >> > > > > is
> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so our
> strings
> > > are
> > > > > > first
> > > > > > >> > > > > prepended
> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > The new proposal does worse when:
> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> > index_type_size
> > > > > > >> > > > > > > in other words when:
> > > > > > >> > > > > > > utf_encoded_string_payload_size < index_type_size
> -
> > 2
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > If the index type ends up being Type.INT32, then
> the
> > > > > > proposal
> > > > > > >> is
> > > > > > >> > > > worse
> > > > > > >> > > > > > when
> > > > > > >> > > > > > > the topic is length 1.
> > > > > > >> > > > > > > If the index type ends up being Type.INT64, then
> the
> > > > > > proposal
> > > > > > >> is
> > > > > > >> > > > worse
> > > > > > >> > > > > > when
> > > > > > >> > > > > > > the topic is less than length 6.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > When compressed:
> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how things
> > > > change
> > > > > > when
> > > > > > >> > > > > > compression
> > > > > > >> > > > > > > comes into the picture. This would be worth
> > > > investigating.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James Cheng <
> > > > > > >> > wushujames@gmail.com
> > > > > > >> > > >
> > > > > > >> > > > > > wrote:
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason Gustafson
> <
> > > > > > >> > > > jason@confluent.io>
> > > > > > >> > > > > > > > wrote:
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay out the
> > > > > assignment
> > > > > > >> > without
> > > > > > >> > > > > > needing
> > > > > > >> > > > > > > > to
> > > > > > >> > > > > > > > > explicitly repeat the topic? For example, the
> > > leader
> > > > > > could
> > > > > > >> > sort
> > > > > > >> > > > the
> > > > > > >> > > > > > > > topics
> > > > > > >> > > > > > > > > for each member and just use an integer to
> > > represent
> > > > > the
> > > > > > >> > index
> > > > > > >> > > of
> > > > > > >> > > > > > each
> > > > > > >> > > > > > > > > topic within the sorted list (note this
> depends
> > on
> > > > the
> > > > > > >> > > > subscription
> > > > > > >> > > > > > > > > including the full topic list).
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]]
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > Jason, doesn't gzip (or other compression)
> > basically
> > > > do
> > > > > > >> this?
> > > > > > >> > If
> > > > > > >> > > > the
> > > > > > >> > > > > > > topic
> > > > > > >> > > > > > > > is a string and the topic is repeated
> throughout,
> > > > won't
> > > > > > >> > > compression
> > > > > > >> > > > > > > > basically replace all repeated instances of it
> > with
> > > an
> > > > > > index
> > > > > > >> > > > > reference
> > > > > > >> > > > > > to
> > > > > > >> > > > > > > > the full string?
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > -James
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > > You could even combine these two options so
> that
> > > you
> > > > > > have
> > > > > > >> > only
> > > > > > >> > > 3
> > > > > > >> > > > > > > integers
> > > > > > >> > > > > > > > > for each topic assignment:
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition
> > > MaxPartition]
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > There may even be better options with a little
> > > more
> > > > > > >> thought.
> > > > > > >> > > All
> > > > > > >> > > > of
> > > > > > >> > > > > > > this
> > > > > > >> > > > > > > > is
> > > > > > >> > > > > > > > > just part of the client-side protocol, so it
> > > > wouldn't
> > > > > > >> require
> > > > > > >> > > any
> > > > > > >> > > > > > > version
> > > > > > >> > > > > > > > > bumps on the broker. What do you think?
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Thanks,
> > > > > > >> > > > > > > > > Jason
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM, Guozhang
> Wang <
> > > > > > >> > > > wangguoz@gmail.com
> > > > > > >> > > > > >
> > > > > > >> > > > > > > > wrote:
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > >> The original concern is that regex may not be
> > > > > > efficiently
> > > > > > >> > > > > supported
> > > > > > >> > > > > > > > >> across-languages, but if there is a neat
> > > > workaround I
> > > > > > >> would
> > > > > > >> > > love
> > > > > > >> > > > > to
> > > > > > >> > > > > > > > learn.
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >> Guozhang
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM, Ismael Juma
> <
> > > > > > >> > > ismael@juma.me.uk
> > > > > > >> > > > >
> > > > > > >> > > > > > > wrote:
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>> Having said that, as a general point, I
> think
> > we
> > > > > > should
> > > > > > >> > > > consider
> > > > > > >> > > > > > > > >> supporting
> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol. It
> > requires
> > > > > some
> > > > > > >> > > thinking
> > > > > > >> > > > > for
> > > > > > >> > > > > > > > >>> cross-language support, but it seems
> > > surmountable
> > > > > and
> > > > > > it
> > > > > > >> > > could
> > > > > > >> > > > > make
> > > > > > >> > > > > > > > >> certain
> > > > > > >> > > > > > > > >>> operations a lot more efficient (the fact
> > that a
> > > > > basic
> > > > > > >> > regex
> > > > > > >> > > > > > > > subscription
> > > > > > >> > > > > > > > >>> causes the consumer to request metadata for
> > all
> > > > > topics
> > > > > > >> is
> > > > > > >> > not
> > > > > > >> > > > > > great).
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>> Ismael
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM, Guozhang
> > Wang
> > > <
> > > > > > >> > > > > > wangguoz@gmail.com>
> > > > > > >> > > > > > > > >>> wrote:
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing the
> > > handling
> > > > > > >> logics of
> > > > > > >> > > > > single
> > > > > > >> > > > > > > > large
> > > > > > >> > > > > > > > >>>> message on the consumer side.
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>> As for the case of "a single group
> > subscribing
> > > to
> > > > > > 3000
> > > > > > >> > > > topics",
> > > > > > >> > > > > > with
> > > > > > >> > > > > > > > >> 100
> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is reasonable
> > to
> > > me
> > > > > > (when
> > > > > > >> > > > storing
> > > > > > >> > > > > in
> > > > > > >> > > > > > > ZK,
> > > > > > >> > > > > > > > >> we
> > > > > > >> > > > > > > > >>>> also have the znode limit which is set to
> 1Mb
> > > by
> > > > > > >> default,
> > > > > > >> > > > though
> > > > > > >> > > > > > > > >>> admittedly
> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if we do
> > the
> > > > > change
> > > > > > >> as
> > > > > > >> > Jun
> > > > > > >> > > > > > > > suggested,
> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure is OK I
> > > > think.
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>> Guozhang
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM, Onur
> > Karaman
> > > <
> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> > > > > > >> > > > > > > > >>>>> wrote:
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>>> Results without compression:
> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the tipping
> > point
> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> > > > > > >> > > > > > > > >>>>>
> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression shrinks
> > the
> > > > > > message
> > > > > > >> > size
> > > > > > >> > > by
> > > > > > >> > > > > 4x.
> > > > > > >> > > > > > > > >>>>>
> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM, Jun Rao <
> > > > > > >> > jun@confluent.io
> > > > > > >> > > >
> > > > > > >> > > > > > wrote:
> > > > > > >> > > > > > > > >>>>>
> > > > > > >> > > > > > > > >>>>>> Onur,
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how we deal
> > > with
> > > > > the
> > > > > > >> case
> > > > > > >> > > > when a
> > > > > > >> > > > > > > > >>> message
> > > > > > >> > > > > > > > >>>> is
> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today, if the
> > > fetch
> > > > > > size
> > > > > > >> is
> > > > > > >> > > > > smaller
> > > > > > >> > > > > > > > >> than
> > > > > > >> > > > > > > > >>>> the
> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get stuck.
> > > > Instead,
> > > > > > we
> > > > > > >> can
> > > > > > >> > > > > simply
> > > > > > >> > > > > > > > >>> return
> > > > > > >> > > > > > > > >>>>> the
> > > > > > >> > > > > > > > >>>>>> full message if it's larger than the
> fetch
> > > size
> > > > > w/o
> > > > > > >> > > > requiring
> > > > > > >> > > > > > the
> > > > > > >> > > > > > > > >>>>> consumer
> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size. On the
> > > > broker
> > > > > > >> side,
> > > > > > >> > to
> > > > > > >> > > > > serve
> > > > > > >> > > > > > a
> > > > > > >> > > > > > > > >>> fetch
> > > > > > >> > > > > > > > >>>>>> request, we already do an index lookup
> and
> > > then
> > > > > > scan
> > > > > > >> the
> > > > > > >> > > > log a
> > > > > > >> > > > > > bit
> > > > > > >> > > > > > > > >> to
> > > > > > >> > > > > > > > >>>>> find
> > > > > > >> > > > > > > > >>>>>> the message with the requested offset. We
> > can
> > > > > just
> > > > > > >> check
> > > > > > >> > > the
> > > > > > >> > > > > > size
> > > > > > >> > > > > > > > >> of
> > > > > > >> > > > > > > > >>>> that
> > > > > > >> > > > > > > > >>>>>> message and return the full message if
> its
> > > size
> > > > > is
> > > > > > >> > larger
> > > > > > >> > > > than
> > > > > > >> > > > > > the
> > > > > > >> > > > > > > > >>>> fetch
> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is really for
> > > > > > performance
> > > > > > >> > > > > > optimization,
> > > > > > >> > > > > > > > >>> i.e.
> > > > > > >> > > > > > > > >>>>> in
> > > > > > >> > > > > > > > >>>>>> the common case, we will not return more
> > > bytes
> > > > > than
> > > > > > >> > fetch
> > > > > > >> > > > > size,
> > > > > > >> > > > > > > but
> > > > > > >> > > > > > > > >>> if
> > > > > > >> > > > > > > > >>>>>> there is a large message, we will return
> > more
> > > > > bytes
> > > > > > >> than
> > > > > > >> > > the
> > > > > > >> > > > > > > > >>> specified
> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large messages
> are
> > > > rare.
> > > > > > >> So, it
> > > > > > >> > > > > > shouldn't
> > > > > > >> > > > > > > > >>>>> increase
> > > > > > >> > > > > > > > >>>>>> the memory consumption on the client too
> > > much.
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>> Jun
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM, Onur
> > > Karaman <
> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> > > > > > >> > > > > > > > >>>>>> wrote:
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing some
> > tests
> > > on
> > > > > the
> > > > > > >> new
> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more strenuous
> > use
> > > > > cases
> > > > > > >> like
> > > > > > >> > > > > > mirroring
> > > > > > >> > > > > > > > >>>>>> clusters
> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and thought I'd
> > > share
> > > > > > >> > whatever I
> > > > > > >> > > > > have
> > > > > > >> > > > > > so
> > > > > > >> > > > > > > > >>>> far.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount of
> group
> > > > > > metadata
> > > > > > >> we
> > > > > > >> > > can
> > > > > > >> > > > > fit
> > > > > > >> > > > > > > > >> into
> > > > > > >> > > > > > > > >>>> one
> > > > > > >> > > > > > > > >>>>>>> message
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Some background:
> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is implemented in
> > two
> > > > > > phases
> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase that
> > > identifies
> > > > > > >> members
> > > > > > >> > of
> > > > > > >> > > > the
> > > > > > >> > > > > > > > >> group
> > > > > > >> > > > > > > > >>>> and
> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions.
> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that waits for
> > the
> > > > > group
> > > > > > >> > leader
> > > > > > >> > > to
> > > > > > >> > > > > > > > >> decide
> > > > > > >> > > > > > > > >>>>> member
> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
> > > subscriptions
> > > > > > across
> > > > > > >> > the
> > > > > > >> > > > > group.
> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this decision
> > with a
> > > > > > >> > > > > SyncGroupRequest.
> > > > > > >> > > > > > > > >> The
> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> SyncGroupRequests
> > > by
> > > > > > >> appending
> > > > > > >> > > all
> > > > > > >> > > > > > group
> > > > > > >> > > > > > > > >>>> state
> > > > > > >> > > > > > > > >>>>>>> into a single message under the
> > > > > __consumer_offsets
> > > > > > >> > topic.
> > > > > > >> > > > > This
> > > > > > >> > > > > > > > >>>> message
> > > > > > >> > > > > > > > >>>>> is
> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and contains each
> > > member
> > > > > > >> > > subscription
> > > > > > >> > > > > as
> > > > > > >> > > > > > > > >> well
> > > > > > >> > > > > > > > >>>> as
> > > > > > >> > > > > > > > >>>>>> the
> > > > > > >> > > > > > > > >>>>>>> decided assignment for each member.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> The environment:
> > > > > > >> > > > > > > > >>>>>>> - one broker
> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets partition
> > > > > > >> > > > > > > > >>>>>>> - offsets.topic.compression.codec=1 //
> > this
> > > is
> > > > > > gzip
> > > > > > >> > > > > > > > >>>>>>> - broker has my pending KAFKA-3718 patch
> > > that
> > > > > > >> actually
> > > > > > >> > > > makes
> > > > > > >> > > > > > use
> > > > > > >> > > > > > > > >> of
> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec:
> > > > > > >> > > > > > > > >>>>>>
> https://github.com/apache/kafka/pull/1394
> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an actual
> > > subset
> > > > > of
> > > > > > >> > topics
> > > > > > >> > > > from
> > > > > > >> > > > > > one
> > > > > > >> > > > > > > > >>> of
> > > > > > >> > > > > > > > >>>>> our
> > > > > > >> > > > > > > > >>>>>>> clusters.
> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long on
> average
> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number of
> > > consumers
> > > > > > each
> > > > > > >> > > > hardcoded
> > > > > > >> > > > > > > > >> with
> > > > > > >> > > > > > > > >>>> all
> > > > > > >> > > > > > > > >>>>>> the
> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests more
> > > consistent.
> > > > > > >> > > wildcarding
> > > > > > >> > > > > with
> > > > > > >> > > > > > > > >> .*
> > > > > > >> > > > > > > > >>>>> should
> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> subscription
> > > > hits
> > > > > > the
> > > > > > >> > > > > coordinator
> > > > > > >> > > > > > > > >> as
> > > > > > >> > > > > > > > >>>> the
> > > > > > >> > > > > > > > >>>>>>> subscription has already been fully
> > expanded
> > > > out
> > > > > > to
> > > > > > >> the
> > > > > > >> > > > list
> > > > > > >> > > > > of
> > > > > > >> > > > > > > > >>>> topics
> > > > > > >> > > > > > > > >>>>> by
> > > > > > >> > > > > > > > >>>>>>> the consumers.
> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to Log.scala
> > to
> > > > > print
> > > > > > >> out
> > > > > > >> > the
> > > > > > >> > > > > > message
> > > > > > >> > > > > > > > >>>> sizes
> > > > > > >> > > > > > > > >>>>>>> after compression
> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all and auto
> > > > commits
> > > > > > are
> > > > > > >> > > > > disabled.
> > > > > > >> > > > > > > > >> The
> > > > > > >> > > > > > > > >>>> only
> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added is the
> > > > > > >> > > __consumer_offsets
> > > > > > >> > > > > > topic
> > > > > > >> > > > > > > > >>> and
> > > > > > >> > > > > > > > >>>>>>> they're only from storing group metadata
> > > while
> > > > > > >> > processing
> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Results:
> > > > > > >> > > > > > > > >>>>>>> The results below show that we exceed
> the
> > > > > 1000012
> > > > > > >> byte
> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit
> > relatively
> > > > > > quickly
> > > > > > >> > > > (between
> > > > > > >> > > > > > > > >> 30-40
> > > > > > >> > > > > > > > >>>>>>> consumers):
> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the tipping
> > > point
> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is pretty
> > > gradual.
> > > > > > >> Plotting
> > > > > > >> > > the
> > > > > > >> > > > > > > > >> points
> > > > > > >> > > > > > > > >>>>> makes
> > > > > > >> > > > > > > > >>>>>> it
> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the number of
> > > > > consumers:
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > >
> > > > > > >> > > >
> > > > > > >> > >
> > > > > > >> >
> > > > > > >>
> > > > > >
> > > > >
> > > >
> > >
> >
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers aren't
> > averages
> > > > or
> > > > > > >> medians
> > > > > > >> > > or
> > > > > > >> > > > > > > > >> anything
> > > > > > >> > > > > > > > >>>>> like
> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size from a
> given
> > > > run.
> > > > > I
> > > > > > >> did
> > > > > > >> > run
> > > > > > >> > > > > them
> > > > > > >> > > > > > a
> > > > > > >> > > > > > > > >>> few
> > > > > > >> > > > > > > > >>>>>> times
> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Impact:
> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> > > > __consumer_offsets
> > > > > > >> topic
> > > > > > >> > > with
> > > > > > >> > > > > my
> > > > > > >> > > > > > > > >>>> pending
> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the AwaitingSync phase
> > of
> > > > the
> > > > > > >> group
> > > > > > >> > > fails
> > > > > > >> > > > > > with
> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This means the
> > > > combined
> > > > > > >> size
> > > > > > >> > of
> > > > > > >> > > > each
> > > > > > >> > > > > > > > >>>> member's
> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments exceeded
> the
> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> > > > > > >> > > > > > > > >>>>> of
> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up dying.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Options:
> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the number of
> > > > consumers
> > > > > > in
> > > > > > >> the
> > > > > > >> > > > > group.
> > > > > > >> > > > > > > > >> This
> > > > > > >> > > > > > > > >>>>> isn't
> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more
> > strenuous
> > > > use
> > > > > > >> cases
> > > > > > >> > > like
> > > > > > >> > > > > > > > >>>> MirrorMaker
> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group into
> > > smaller
> > > > > > >> groups
> > > > > > >> > > which
> > > > > > >> > > > > > > > >>> together
> > > > > > >> > > > > > > > >>>>> will
> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics. This
> > gives
> > > > each
> > > > > > >> group
> > > > > > >> > > > > member a
> > > > > > >> > > > > > > > >>>> smaller
> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics starting
> > > with
> > > > > a-m
> > > > > > >> while
> > > > > > >> > > g2
> > > > > > >> > > > > has
> > > > > > >> > > > > > > > >>> topics
> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be
> > > operationally
> > > > > > >> painful
> > > > > > >> > to
> > > > > > >> > > > > > manage.
> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the topics among
> > > > members
> > > > > > of
> > > > > > >> the
> > > > > > >> > > > > group.
> > > > > > >> > > > > > > > >>> Again
> > > > > > >> > > > > > > > >>>>> this
> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller
> > > > subscription.
> > > > > > This
> > > > > > >> > > would
> > > > > > >> > > > > also
> > > > > > >> > > > > > > > >> be
> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage.
> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> > > > > > >> KafkaConfig.messageMaxBytes
> > > > > > >> > (a
> > > > > > >> > > > > > > > >>> topic-level
> > > > > > >> > > > > > > > >>>>>>> config) and
> > KafkaConfig.replicaFetchMaxBytes
> > > > (a
> > > > > > >> > > > broker-level
> > > > > > >> > > > > > > > >>> config).
> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just the
> > > > > > >> __consumer_offsets
> > > > > > >> > > > topic
> > > > > > >> > > > > > > > >> seems
> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping up the
> > > > > > broker-level
> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> > > > > > >> > > > > > > > >>>>>>> would probably need more attention.
> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
> > compression
> > > > > > codecs.
> > > > > > >> > Based
> > > > > > >> > > > on
> > > > > > >> > > > > 2
> > > > > > >> > > > > > > > >>>> minutes
> > > > > > >> > > > > > > > >>>>> of
> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and snappy
> are
> > > > > faster
> > > > > > >> than
> > > > > > >> > > gzip
> > > > > > >> > > > > but
> > > > > > >> > > > > > > > >>> have
> > > > > > >> > > > > > > > >>>>>> worse
> > > > > > >> > > > > > > > >>>>>>> compression, so this probably won't
> help.
> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support
> sending
> > > the
> > > > > > regex
> > > > > > >> > over
> > > > > > >> > > > the
> > > > > > >> > > > > > wire
> > > > > > >> > > > > > > > >>>>> instead
> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> > subscriptions. I
> > > > > think
> > > > > > >> > people
> > > > > > >> > > > > said
> > > > > > >> > > > > > in
> > > > > > >> > > > > > > > >>> the
> > > > > > >> > > > > > > > >>>>>> past
> > > > > > >> > > > > > > > >>>>>>> that different languages have subtle
> > > > differences
> > > > > > in
> > > > > > >> > > regex,
> > > > > > >> > > > so
> > > > > > >> > > > > > > > >> this
> > > > > > >> > > > > > > > >>>>>> doesn't
> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language groups.
> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe we can
> > > reverse
> > > > > the
> > > > > > >> > > mapping?
> > > > > > >> > > > > > > > >> Instead
> > > > > > >> > > > > > > > >>>> of
> > > > > > >> > > > > > > > >>>>>>> mapping from member to subscriptions, we
> > can
> > > > > map a
> > > > > > >> > > > > subscription
> > > > > > >> > > > > > > > >> to
> > > > > > >> > > > > > > > >>> a
> > > > > > >> > > > > > > > >>>>> list
> > > > > > >> > > > > > > > >>>>>>> of members.
> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe we can
> try
> > > to
> > > > > > break
> > > > > > >> > apart
> > > > > > >> > > > the
> > > > > > >> > > > > > > > >>>>>> subscription
> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> > > SyncGroupRequest
> > > > > > into
> > > > > > >> > > > multiple
> > > > > > >> > > > > > > > >>> records?
> > > > > > >> > > > > > > > >>>>>> They
> > > > > > >> > > > > > > > >>>>>>> can still go to the same message set and
> > get
> > > > > > >> appended
> > > > > > >> > > > > together.
> > > > > > >> > > > > > > > >>> This
> > > > > > >> > > > > > > > >>>>> way
> > > > > > >> > > > > > > > >>>>>>> the limit become the segment size, which
> > > > > shouldn't
> > > > > > >> be a
> > > > > > >> > > > > > problem.
> > > > > > >> > > > > > > > >>> This
> > > > > > >> > > > > > > > >>>>> can
> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because we're
> > > currently
> > > > > > >> keying
> > > > > > >> > > these
> > > > > > >> > > > > > > > >>> messages
> > > > > > >> > > > > > > > >>>> on
> > > > > > >> > > > > > > > >>>>>> the
> > > > > > >> > > > > > > > >>>>>>> group, so I think records from the same
> > > > > rebalance
> > > > > > >> might
> > > > > > >> > > > > > > > >>> accidentally
> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> understanding
> > of
> > > > > > >> compaction
> > > > > > >> > > > isn't
> > > > > > >> > > > > > > > >> that
> > > > > > >> > > > > > > > >>>>> great.
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> Todo:
> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun the
> tests
> > > > with
> > > > > no
> > > > > > >> > > > > compression
> > > > > > >> > > > > > > > >> just
> > > > > > >> > > > > > > > >>>> to
> > > > > > >> > > > > > > > >>>>>> see
> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's
> getting
> > > > late.
> > > > > > >> Maybe
> > > > > > >> > > > > tomorrow?
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>> - Onur
> > > > > > >> > > > > > > > >>>>>>>
> > > > > > >> > > > > > > > >>>>>>
> > > > > > >> > > > > > > > >>>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>> --
> > > > > > >> > > > > > > > >>>> -- Guozhang
> > > > > > >> > > > > > > > >>>>
> > > > > > >> > > > > > > > >>>
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > > >> --
> > > > > > >> > > > > > > > >> -- Guozhang
> > > > > > >> > > > > > > > >>
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > >
> > > > > > >> > > >
> > > > > > >> > >
> > > > > > >> >
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > --
> > > > > > >> > -- Guozhang
> > > > > > >> >
> > > > > > >>
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Jason Gustafson <ja...@confluent.io>]

Hey Becket,

My suggestion was pretty far from a completely thought-out proposal, but
the advantages of having your MM cluster maintain subscriptions/assignments
in its own topic are the following:

1. It solves the immediate problem of the size of the group metadata.
2. It distributes the subscription/assignment data among the brokers, so
the coordinator is not a bottleneck.
3. Subscriptions are fixed at startup, so maybe you only need to write them
once, which saves some network overhead on each rebalance. The leader is
currently sticky as well, so perhaps you could cache them and save lookup
overhead, which probably doesn't have much of an impact on memory since
subscriptions are typically the same for all consumers (except during
rolling update).

The disadvantage is that it's clearly more complex than letting the
coordinator do all the work. But it seems at this point like the other
solutions are more like workarounds.

-Jason




On Thu, Jun 9, 2016 at 10:52 PM, Becket Qin <be...@gmail.com> wrote:

> Hi Jason,
>
> I am trying to understand the gain of saving the assignment and metadata in
> a topic and return the offsets to the consumers. This obviously saves
> memory footprint as we agreed before. But does it save network bandwidth?
> The consumers still need to read the same amount of data from the
> coordinator broker, right?
>
> In terms of the current proposal, Onur and I discussed offline. It looks
> that having a separate "offset.replica.fetch.max.bytes" does not buy us
> much. Users are likely setting it to be the same value as the max message
> size of the __consumer_offsets topic. The reason is this configuration is
> mainly for consumer side memory management, the users would not want to set
> it to be bigger than necessary.
>
> The solution we discussed is what Jun suggested, i.e. look at the size of
> the first message returned. If the size of the message is greater than the
> fetch max bytes, we always return the first message even it is bigger than
> max fetch size. Otherwise we only return up to fetch max bytes. We only do
> this for __consumer_offsets topic so no user topic will be impacted.
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
> On Thu, Jun 9, 2016 at 2:40 PM, Jason Gustafson <ja...@confluent.io>
> wrote:
>
> > Hi Onur,
> >
> > I didn't have a specific proposal in mind, I was just thinking
> analogously
> > with how Connect ensures task configurations are propagated to tasks
> > consistently when it rebalances the cluster. The high level concept is to
> > take the assignment data out of the rebalance protocol itself and replace
> > it with a pointer. For example, the pointer can be a (topic, partition,
> > offset) tuple which can be fetched separately by the consumer instance
> > after the rebalance completes. Then the leader would generate the
> > assignments, write them to Kafka, and send the pointers to the rest of
> the
> > group in the SyncGroup. This is more or less how Connect works.
> >
> > -Jason
> >
> > On Thu, Jun 9, 2016 at 11:10 AM, Onur Karaman
> > <okaraman@linkedin.com.invalid
> > > wrote:
> >
> > > I think the value of adding a "offsets.replica.fetch.max.bytes" config
> is
> > > that we don't break/change the meaning of "replica.fetch.max.bytes".
> > >
> > > We can also set "offsets.replica.fetch.max.bytes" to be a value safely
> > > larger than what we expect to ever allow the __consumer_offsets topic
> max
> > > message size to be without doing the larger change of bumping up the
> > global
> > > "replica.fetch.max.bytes".
> > >
> > > On Thu, Jun 9, 2016 at 10:40 AM, Becket Qin <be...@gmail.com>
> > wrote:
> > >
> > > > I think taking bigger one of the fetch size and message size limit is
> > > > probably good enough. If we have a separate
> > > > "offset.replica.fetch.max.bytes", I guess the value will always be
> set
> > to
> > > > max message size of the __consumer_offsets topic, which does not seem
> > to
> > > > have much value.
> > > >
> > > > On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman
> > > <okaraman@linkedin.com.invalid
> > > > >
> > > > wrote:
> > > >
> > > > > Maybe another approach can be to add a new
> > > > > "offsets.replica.fetch.max.bytes" config on the brokers.
> > > > >
> > > > > On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <
> okaraman@linkedin.com>
> > > > > wrote:
> > > > >
> > > > > > I made a PR with a tweak to Jun's/Becket's proposal:
> > > > > > https://github.com/apache/kafka/pull/1484
> > > > > >
> > > > > > It just tweaks the fetch behavior specifically for replicas
> > fetching
> > > > from
> > > > > > the __consumer_offsets topic when the fetcher's
> > > > "replica.fetch.max.bytes"
> > > > > > is less than the __consumer_offset leader's "message.max.bytes"
> to
> > > take
> > > > > the
> > > > > > max of the two.
> > > > > >
> > > > > > I'm honestly not that happy with this solution, as I'd rather not
> > > > change
> > > > > > the "replica.fetch.max.bytes" config from being a limit to a
> > > > > > recommendation. I'd definitely be happy to hear other
> alternatives!
> > > > > >
> > > > > > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> > > > > > onurkaraman.apache@gmail.com> wrote:
> > > > > >
> > > > > >> Sorry I know next to nothing about Kafka Connect. I didn't
> > > understand
> > > > > the
> > > > > >> Kafka Connect / MM idea you brought up. Can you go into more
> > detail?
> > > > > >>
> > > > > >> Otherwise I think our remaining options are:
> > > > > >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes
> for
> > > > > >> __consumer_offsets topic and change the fetch behavior when
> > message
> > > > size
> > > > > >> is
> > > > > >> larger than fetch size
> > > > > >> - option 6: support sending the regex over the wire instead of
> the
> > > > fully
> > > > > >> expanded topic subscriptions. This should cut down the message
> > size
> > > > from
> > > > > >> the subscription side. Again this only helps when pattern-based
> > > > > >> subscriptions are done.
> > > > > >>
> > > > > >> minor correction to an earlier comment I made regarding the
> > message
> > > > > size:
> > > > > >> message size ~ sum(s_i + a_i for i in range [1, |C|])
> > > > > >>
> > > > > >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <
> > > jason@confluent.io>
> > > > > >> wrote:
> > > > > >>
> > > > > >> > Hey Onur,
> > > > > >> >
> > > > > >> > Thanks for the investigation. It seems the conclusion is that
> > the
> > > > > >> compact
> > > > > >> > format helps, but perhaps not enough to justify adding a new
> > > > > assignment
> > > > > >> > schema? I'm not sure there's much more room for savings unless
> > we
> > > > > change
> > > > > >> > something more fundamental in the assignment approach. We
> spent
> > > some
> > > > > >> time
> > > > > >> > thinking before about whether we could let the consumers
> compute
> > > > their
> > > > > >> > assignment locally from a smaller set of information, but the
> > > > > difficulty
> > > > > >> > (I'm sure you remember) is reaching consensus on topic
> metadata.
> > > > Kafka
> > > > > >> > Connect has a similar problem where all the workers need to
> > agree
> > > on
> > > > > >> > connector configurations. Since all configs are stored in a
> > single
> > > > > topic
> > > > > >> > partition, the approach we take there is to propagate the
> offset
> > > in
> > > > > the
> > > > > >> > assignment protocol. Not sure if we could do something similar
> > for
> > > > > MM...
> > > > > >> > Anyway, it seems like the best workaround at the moment is
> Jun's
> > > > > initial
> > > > > >> > suggestion. What do you think?
> > > > > >> >
> > > > > >> > -Jason
> > > > > >> >
> > > > > >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> > > > > >> > onurkaraman.apache@gmail.com
> > > > > >> > > wrote:
> > > > > >> >
> > > > > >> > > I gave the topic index assignment trick a try against the
> same
> > > > > >> > environment.
> > > > > >> > > The implementation just changed the assignment serialization
> > and
> > > > > >> > > deserialization logic. It didn't change SyncGroupResponse,
> > > meaning
> > > > > it
> > > > > >> > > continues to exclude the subscription from the
> > SyncGroupResponse
> > > > and
> > > > > >> > > assumes the member has kept track of its last subscription.
> > > > > >> > >
> > > > > >> > > Assignment topic indexing with compression:
> > > > > >> > > 1 consumer 34346 bytes
> > > > > >> > > 5 consumers 177687 bytes
> > > > > >> > > 10 consumers 331897 bytes
> > > > > >> > > 20 consumers 572467 bytes
> > > > > >> > > 30 consumers 811269 bytes
> > > > > >> > > 40 consumers 1047188 bytes * the tipping point
> > > > > >> > > 50 consumers 1290092 bytes
> > > > > >> > > 60 consumers 1527806 bytes
> > > > > >> > > 70 consumers 1769259 bytes
> > > > > >> > > 80 consumers 2000118 bytes
> > > > > >> > > 90 consumers 2244392 bytes
> > > > > >> > > 100 consumers 2482415 bytes
> > > > > >> > >
> > > > > >> > > Assignment topic indexing without compression:
> > > > > >> > > 1 consumer 211904 bytes
> > > > > >> > > 5 consumers 677184 bytes
> > > > > >> > > 10 consumers 1211154 bytes * the tipping point
> > > > > >> > > 20 consumers 2136196 bytes
> > > > > >> > > 30 consumers 3061238 bytes
> > > > > >> > > 40 consumers 3986280 bytes
> > > > > >> > > 50 consumers 4911322 bytes
> > > > > >> > > 60 consumers 5836284 bytes
> > > > > >> > > 70 consumers 6761246 bytes
> > > > > >> > > 80 consumers 7686208 bytes
> > > > > >> > > 90 consumers 8611170 bytes
> > > > > >> > > 100 consumers 9536132 bytes
> > > > > >> > >
> > > > > >> > > Assignment topic indexing seems to reduce the size by 500KB
> > > > without
> > > > > >> > > compression and 80KB with compression. So assignment topic
> > > > indexing
> > > > > >> makes
> > > > > >> > > some difference in both with and without compression but in
> > our
> > > > case
> > > > > >> was
> > > > > >> > > not nearly enough.
> > > > > >> > >
> > > > > >> > > This can be explained by the fact that we aren't actually
> > > hitting
> > > > > the
> > > > > >> > worst
> > > > > >> > > case scenario of each consumer being assigned a partition
> from
> > > > every
> > > > > >> > topic.
> > > > > >> > > The reason is simple: a topic can only fully span all the
> > > > consumers
> > > > > >> if it
> > > > > >> > > has at least as many partitions as there are consumers.
> Given
> > > that
> > > > > >> there
> > > > > >> > > are 8 partitions per topic and we have 100 consumers, it
> makes
> > > > sense
> > > > > >> that
> > > > > >> > > we aren't close to this worse case scenario where topic
> > indexing
> > > > > would
> > > > > >> > make
> > > > > >> > > a bigger difference.
> > > > > >> > >
> > > > > >> > > I tweaked the group leader's assignment code to print out
> the
> > > > > >> assignments
> > > > > >> > > and found that each consumer was getting either 238 or 239
> > > > > partitions.
> > > > > >> > Each
> > > > > >> > > of these partitions were from unique topics. So the
> consumers
> > > were
> > > > > >> really
> > > > > >> > > getting partitions from 239 topics instead of the full worst
> > > case
> > > > > >> > scenario
> > > > > >> > > of 3000 topics.
> > > > > >> > >
> > > > > >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <
> > > > > jason@confluent.io>
> > > > > >> > > wrote:
> > > > > >> > >
> > > > > >> > > > Gwen, Joel:
> > > > > >> > > >
> > > > > >> > > > That's correct. The protocol does allow us to give an
> > assignor
> > > > its
> > > > > >> own
> > > > > >> > > > assignment schema, but I think this will require a couple
> > > > internal
> > > > > >> > > changes
> > > > > >> > > > to the consumer to make use of the full generality.
> > > > > >> > > >
> > > > > >> > > > One thing I'm a little uncertain about is whether we
> should
> > > use
> > > > a
> > > > > >> > > different
> > > > > >> > > > protocol type. For a little context, the group membership
> > > > protocol
> > > > > >> > allows
> > > > > >> > > > the client to provide a "protocol type" when joining the
> > group
> > > > to
> > > > > >> > ensure
> > > > > >> > > > that all members have some basic semantic compatibility.
> For
> > > > > >> example,
> > > > > >> > the
> > > > > >> > > > consumer uses "consumer" and Kafka Connect uses "connect."
> > > > > Currently
> > > > > >> > all
> > > > > >> > > > assignors using the "consumer" protocol share a common
> > schema
> > > > for
> > > > > >> > > > representing subscriptions and assignment. This is
> > convenient
> > > > for
> > > > > >> tools
> > > > > >> > > > (like consumer-groups.sh) since they just need to know how
> > to
> > > > > parse
> > > > > >> the
> > > > > >> > > > "consumer" protocol type without knowing anything about
> the
> > > > > >> assignors.
> > > > > >> > So
> > > > > >> > > > introducing another schema would break that assumption and
> > > we'd
> > > > > need
> > > > > >> > > those
> > > > > >> > > > tools to do assignor-specific parsing. Maybe this is OK?
> > > > > >> Alternatively,
> > > > > >> > > we
> > > > > >> > > > could use a separate protocol type (e.g.
> > "compact-consumer"),
> > > > but
> > > > > >> that
> > > > > >> > > > seems less than desirable.
> > > > > >> > > >
> > > > > >> > > > Thanks,
> > > > > >> > > > Jason
> > > > > >> > > >
> > > > > >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <
> > > > gwen@confluent.io
> > > > > >
> > > > > >> > > wrote:
> > > > > >> > > >
> > > > > >> > > > > ah, right - we can add as many strategies as we want.
> > > > > >> > > > >
> > > > > >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <
> > > > > jjkoshy.w@gmail.com
> > > > > >> >
> > > > > >> > > > wrote:
> > > > > >> > > > >
> > > > > >> > > > > > > Yes it would be a protocol bump.
> > > > > >> > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > Sorry - I'm officially confused. I think it may not be
> > > > > required
> > > > > >> -
> > > > > >> > > since
> > > > > >> > > > > the
> > > > > >> > > > > > more compact format would be associated with a new
> > > > assignment
> > > > > >> > > strategy
> > > > > >> > > > -
> > > > > >> > > > > > right?
> > > > > >> > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > > smaller than the plaintext PAL, but the
> > post-compressed
> > > > > binary
> > > > > >> > PAL
> > > > > >> > > is
> > > > > >> > > > > > just
> > > > > >> > > > > > > 25% smaller than the post-compressed plaintext PAL.
> > IOW
> > > > > using
> > > > > >> a
> > > > > >> > > > symbol
> > > > > >> > > > > > > table helps a lot but further compression on that
> > > already
> > > > > >> compact
> > > > > >> > > > > format
> > > > > >> > > > > > > would yield only marginal return.
> > > > > >> > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > > So basically I feel we could get pretty far with a
> > more
> > > > > >> compact
> > > > > >> > > field
> > > > > >> > > > > > > format for assignment and if we do that then we
> would
> > > > > >> potentially
> > > > > >> > > not
> > > > > >> > > > > > even
> > > > > >> > > > > > > want to do any compression.
> > > > > >> > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > Also just wanted to add that this compression on the
> > > binary
> > > > > PAL
> > > > > >> did
> > > > > >> > > > help
> > > > > >> > > > > > but the compression ratio was obviously not as high as
> > > > > plaintext
> > > > > >> > > > > > compression.
> > > > > >> > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > >
> > > > > >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> > > > > >> gwen@confluent.io
> > > > > >> > >
> > > > > >> > > > > wrote:
> > > > > >> > > > > > >
> > > > > >> > > > > > >> Regarding the change to the assignment field. It
> > would
> > > > be a
> > > > > >> > > protocol
> > > > > >> > > > > > bump,
> > > > > >> > > > > > >> otherwise consumers will not know how to parse the
> > > bytes
> > > > > the
> > > > > >> > > broker
> > > > > >> > > > is
> > > > > >> > > > > > >> returning, right?
> > > > > >> > > > > > >> Or did I misunderstand the suggestion?
> > > > > >> > > > > > >>
> > > > > >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> > > > > >> > > wangguoz@gmail.com>
> > > > > >> > > > > > >> wrote:
> > > > > >> > > > > > >>
> > > > > >> > > > > > >> > I think for just solving issue 1), Jun's
> suggestion
> > > is
> > > > > >> > > sufficient
> > > > > >> > > > > and
> > > > > >> > > > > > >> > simple. So I'd prefer that approach.
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> > In addition, Jason's optimization on the
> assignment
> > > > field
> > > > > >> > would
> > > > > >> > > be
> > > > > >> > > > > > good
> > > > > >> > > > > > >> for
> > > > > >> > > > > > >> > 2) and 3) as well, and I like that optimization
> for
> > > its
> > > > > >> > > simplicity
> > > > > >> > > > > and
> > > > > >> > > > > > >> no
> > > > > >> > > > > > >> > format change as well. And in the future I'm in
> > favor
> > > > of
> > > > > >> > > > considering
> > > > > >> > > > > > to
> > > > > >> > > > > > >> > change the in-memory cache format as Jiangjie
> > > > suggested.
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> > Guozhang
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> > > > > >> > > > becket.qin@gmail.com>
> > > > > >> > > > > > >> wrote:
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> > > Hi Jason,
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > There are a few problems we want to solve here:
> > > > > >> > > > > > >> > > 1. The group metadata is too big to be appended
> > to
> > > > the
> > > > > >> log.
> > > > > >> > > > > > >> > > 2. Reduce the memory footprint on the broker
> > > > > >> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > To solve (1), I like your idea of having
> separate
> > > > > >> messages
> > > > > >> > per
> > > > > >> > > > > > member.
> > > > > >> > > > > > >> > The
> > > > > >> > > > > > >> > > proposal (Onur's option 8) is to break metadata
> > > into
> > > > > >> small
> > > > > >> > > > records
> > > > > >> > > > > > in
> > > > > >> > > > > > >> the
> > > > > >> > > > > > >> > > same uncompressed message set so each record is
> > > > small.
> > > > > I
> > > > > >> > agree
> > > > > >> > > > it
> > > > > >> > > > > > >> would
> > > > > >> > > > > > >> > be
> > > > > >> > > > > > >> > > ideal if we are able to store the metadata
> > > separately
> > > > > for
> > > > > >> > each
> > > > > >> > > > > > >> member. I
> > > > > >> > > > > > >> > > was also thinking about storing the metadata
> into
> > > > > >> multiple
> > > > > >> > > > > messages,
> > > > > >> > > > > > >> too.
> > > > > >> > > > > > >> > > What concerns me was that having multiple
> > messages
> > > > > seems
> > > > > >> > > > breaking
> > > > > >> > > > > > the
> > > > > >> > > > > > >> > > atomicity. I am not sure how we are going to
> deal
> > > > with
> > > > > >> the
> > > > > >> > > > > potential
> > > > > >> > > > > > >> > > issues. For example, What if group metadata is
> > > > > replicated
> > > > > >> > but
> > > > > >> > > > the
> > > > > >> > > > > > >> member
> > > > > >> > > > > > >> > > metadata is not? It might be fine depending on
> > the
> > > > > >> > > > implementation
> > > > > >> > > > > > >> though,
> > > > > >> > > > > > >> > > but I am not sure.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > For (2) we want to store the metadata onto the
> > > disk,
> > > > > >> which
> > > > > >> > is
> > > > > >> > > > what
> > > > > >> > > > > > we
> > > > > >> > > > > > >> > have
> > > > > >> > > > > > >> > > to do anyway. The only question is in what
> format
> > > > > should
> > > > > >> we
> > > > > >> > > > store
> > > > > >> > > > > > >> them.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > To address (3) we want to have the metadata to
> be
> > > > > >> > compressed,
> > > > > >> > > > > which
> > > > > >> > > > > > is
> > > > > >> > > > > > >> > > contradict to the the above solution of (1).
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > I think Jun's suggestion is probably still the
> > > > > simplest.
> > > > > >> To
> > > > > >> > > > avoid
> > > > > >> > > > > > >> > changing
> > > > > >> > > > > > >> > > the behavior for consumers, maybe we can do
> that
> > > only
> > > > > for
> > > > > >> > > > > > >> offset_topic,
> > > > > >> > > > > > >> > > i.e, if the max fetch bytes of the fetch
> request
> > is
> > > > > >> smaller
> > > > > >> > > than
> > > > > >> > > > > the
> > > > > >> > > > > > >> > > message size on the offset topic, we always
> > return
> > > at
> > > > > >> least
> > > > > >> > > one
> > > > > >> > > > > full
> > > > > >> > > > > > >> > > message. This should avoid the unexpected
> problem
> > > on
> > > > > the
> > > > > >> > > client
> > > > > >> > > > > side
> > > > > >> > > > > > >> > > because supposedly only tools and brokers will
> > > fetch
> > > > > from
> > > > > >> > the
> > > > > >> > > > the
> > > > > >> > > > > > >> > internal
> > > > > >> > > > > > >> > > topics,
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > As a modification to what you suggested, one
> > > > solution I
> > > > > >> was
> > > > > >> > > > > thinking
> > > > > >> > > > > > >> was
> > > > > >> > > > > > >> > to
> > > > > >> > > > > > >> > > have multiple messages in a single compressed
> > > > message.
> > > > > >> That
> > > > > >> > > > means
> > > > > >> > > > > > for
> > > > > >> > > > > > >> > > SyncGroupResponse we still need to read the
> > entire
> > > > > >> > compressed
> > > > > >> > > > > > messages
> > > > > >> > > > > > >> > and
> > > > > >> > > > > > >> > > extract the inner messages, which seems not
> quite
> > > > > >> different
> > > > > >> > > from
> > > > > >> > > > > > >> having a
> > > > > >> > > > > > >> > > single message containing everything. But let
> me
> > > just
> > > > > >> put it
> > > > > >> > > > here
> > > > > >> > > > > > and
> > > > > >> > > > > > >> see
> > > > > >> > > > > > >> > > if that makes sense.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > We can have a map of GroupMetadataKey ->
> > > > > >> > > > GroupMetadataValueOffset.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > The GroupMetadataValue is stored in a
> compressed
> > > > > message.
> > > > > >> > The
> > > > > >> > > > > inner
> > > > > >> > > > > > >> > > messages are the following:
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > Inner Message 0: Version GroupId Generation
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we
> > can
> > > > > >> compress
> > > > > >> > > the
> > > > > >> > > > > > bytes
> > > > > >> > > > > > >> > here)
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> > > > > >> > > > > > >> > > ....
> > > > > >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > The MemberMetadata format is the following:
> > > > > >> > > > > > >> > >   MemberMetadata => Version Generation ClientId
> > > Host
> > > > > >> > > > Subscription
> > > > > >> > > > > > >> > > Assignment
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > So DescribeGroupResponse will just return the
> > > entire
> > > > > >> > > compressed
> > > > > >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will
> > return
> > > > the
> > > > > >> > > > > > corresponding
> > > > > >> > > > > > >> > inner
> > > > > >> > > > > > >> > > message.
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > Thanks,
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > Jiangjie (Becket) Qin
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason
> Gustafson
> > <
> > > > > >> > > > > > jason@confluent.io>
> > > > > >> > > > > > >> > > wrote:
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > > Hey Becket,
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > I like your idea to store only the offset for
> > the
> > > > > group
> > > > > >> > > > metadata
> > > > > >> > > > > > in
> > > > > >> > > > > > >> > > memory.
> > > > > >> > > > > > >> > > > I think it would be safe to keep it in memory
> > > for a
> > > > > >> short
> > > > > >> > > time
> > > > > >> > > > > > after
> > > > > >> > > > > > >> > the
> > > > > >> > > > > > >> > > > rebalance completes, but after that, it's
> only
> > > real
> > > > > >> > purpose
> > > > > >> > > is
> > > > > >> > > > > to
> > > > > >> > > > > > >> > answer
> > > > > >> > > > > > >> > > > DescribeGroup requests, so your proposal
> makes
> > a
> > > > lot
> > > > > of
> > > > > >> > > sense
> > > > > >> > > > to
> > > > > >> > > > > > me.
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > As for the specific problem with the size of
> > the
> > > > > group
> > > > > >> > > > metadata
> > > > > >> > > > > > >> message
> > > > > >> > > > > > >> > > for
> > > > > >> > > > > > >> > > > the MM case, if we cannot succeed in reducing
> > the
> > > > > size
> > > > > >> of
> > > > > >> > > the
> > > > > >> > > > > > >> > > > subscription/assignment (which I think is
> still
> > > > > >> probably
> > > > > >> > the
> > > > > >> > > > > best
> > > > > >> > > > > > >> > > > alternative if it can work), then I think
> there
> > > are
> > > > > >> some
> > > > > >> > > > options
> > > > > >> > > > > > for
> > > > > >> > > > > > >> > > > changing the message format (option #8 in
> > Onur's
> > > > > >> initial
> > > > > >> > > > > e-mail).
> > > > > >> > > > > > >> > > > Currently, the key used for storing the group
> > > > > metadata
> > > > > >> is
> > > > > >> > > > this:
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > GroupMetadataKey => Version GroupId
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > And the value is something like this (some
> > > details
> > > > > >> > elided):
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > GroupMetadataValue => Version GroupId
> > Generation
> > > > > >> > > > > [MemberMetadata]
> > > > > >> > > > > > >> > > >   MemberMetadata => ClientId Host
> Subscription
> > > > > >> Assignment
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > I don't think we can change the key without a
> > lot
> > > > of
> > > > > >> pain,
> > > > > >> > > but
> > > > > >> > > > > it
> > > > > >> > > > > > >> seems
> > > > > >> > > > > > >> > > > like we can change the value format. Maybe we
> > can
> > > > > take
> > > > > >> the
> > > > > >> > > > > > >> > > > subscription/assignment payloads out of the
> > value
> > > > and
> > > > > >> > > > introduce
> > > > > >> > > > > a
> > > > > >> > > > > > >> new
> > > > > >> > > > > > >> > > > "MemberMetadata" message for each member in
> the
> > > > > group.
> > > > > >> For
> > > > > >> > > > > > example:
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > MemberMetadataValue => Version Generation
> > > ClientId
> > > > > Host
> > > > > >> > > > > > Subscription
> > > > > >> > > > > > >> > > > Assignment
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > When a new generation is created, we would
> > first
> > > > > write
> > > > > >> the
> > > > > >> > > > group
> > > > > >> > > > > > >> > metadata
> > > > > >> > > > > > >> > > > message which includes the generation and all
> > of
> > > > the
> > > > > >> > > > memberIds,
> > > > > >> > > > > > and
> > > > > >> > > > > > >> > then
> > > > > >> > > > > > >> > > > we'd write the member metadata messages. To
> > > answer
> > > > > the
> > > > > >> > > > > > DescribeGroup
> > > > > >> > > > > > >> > > > request, we'd read the group metadata at the
> > > cached
> > > > > >> offset
> > > > > >> > > > and,
> > > > > >> > > > > > >> > depending
> > > > > >> > > > > > >> > > > on the version, all of the following member
> > > > metadata.
> > > > > >> This
> > > > > >> > > > would
> > > > > >> > > > > > be
> > > > > >> > > > > > >> > more
> > > > > >> > > > > > >> > > > complex to maintain, but it seems doable if
> it
> > > > comes
> > > > > to
> > > > > >> > it.
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > Thanks,
> > > > > >> > > > > > >> > > > Jason
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> > > > > >> > > > > becket.qin@gmail.com
> > > > > >> > > > > > >
> > > > > >> > > > > > >> > > wrote:
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > > It might worth thinking a little further.
> We
> > > have
> > > > > >> > > discussed
> > > > > >> > > > > this
> > > > > >> > > > > > >> > before
> > > > > >> > > > > > >> > > > > that we want to avoid holding all the group
> > > > > metadata
> > > > > >> in
> > > > > >> > > > > memory.
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > I am thinking about the following end
> state:
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > 1. Enable compression on the offset topic.
> > > > > >> > > > > > >> > > > > 2. Instead of holding the entire group
> > metadata
> > > > in
> > > > > >> > memory
> > > > > >> > > on
> > > > > >> > > > > the
> > > > > >> > > > > > >> > > brokers,
> > > > > >> > > > > > >> > > > > each broker only keeps a [group -> Offset]
> > map,
> > > > the
> > > > > >> > offset
> > > > > >> > > > > > points
> > > > > >> > > > > > >> to
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > message in the offset topic which holds the
> > > > latest
> > > > > >> > > metadata
> > > > > >> > > > of
> > > > > >> > > > > > the
> > > > > >> > > > > > >> > > group.
> > > > > >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the
> > > > offset
> > > > > >> topic
> > > > > >> > > > > > directly
> > > > > >> > > > > > >> > like
> > > > > >> > > > > > >> > > a
> > > > > >> > > > > > >> > > > > normal consumption, except that only
> exactly
> > > one
> > > > > >> message
> > > > > >> > > > will
> > > > > >> > > > > be
> > > > > >> > > > > > >> > > > returned.
> > > > > >> > > > > > >> > > > > 4. SyncGroupResponse will read the message,
> > > > extract
> > > > > >> the
> > > > > >> > > > > > assignment
> > > > > >> > > > > > >> > part
> > > > > >> > > > > > >> > > > and
> > > > > >> > > > > > >> > > > > send back the partition assignment. We can
> > > > compress
> > > > > >> the
> > > > > >> > > > > > partition
> > > > > >> > > > > > >> > > > > assignment before sends it out if we want.
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > Jiangjie (Becket) Qin
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason
> > > Gustafson
> > > > <
> > > > > >> > > > > > >> jason@confluent.io
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> > > > > wrote:
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > Jason, doesn't gzip (or other
> > compression)
> > > > > >> basically
> > > > > >> > > do
> > > > > >> > > > > > this?
> > > > > >> > > > > > >> If
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > > topic
> > > > > >> > > > > > >> > > > > > > is a string and the topic is repeated
> > > > > throughout,
> > > > > >> > > won't
> > > > > >> > > > > > >> > compression
> > > > > >> > > > > > >> > > > > > > basically replace all repeated
> instances
> > of
> > > > it
> > > > > >> with
> > > > > >> > an
> > > > > >> > > > > index
> > > > > >> > > > > > >> > > > reference
> > > > > >> > > > > > >> > > > > to
> > > > > >> > > > > > >> > > > > > > the full string?
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > > Hey James, yeah, that's probably true,
> but
> > > keep
> > > > > in
> > > > > >> > mind
> > > > > >> > > > that
> > > > > >> > > > > > the
> > > > > >> > > > > > >> > > > > > compression happens on the broker side.
> It
> > > > would
> > > > > be
> > > > > >> > nice
> > > > > >> > > > to
> > > > > >> > > > > > >> have a
> > > > > >> > > > > > >> > > more
> > > > > >> > > > > > >> > > > > > compact representation so that get some
> > > benefit
> > > > > >> over
> > > > > >> > the
> > > > > >> > > > > wire
> > > > > >> > > > > > as
> > > > > >> > > > > > >> > > well.
> > > > > >> > > > > > >> > > > > This
> > > > > >> > > > > > >> > > > > > seems to be less of a concern here, so
> the
> > > > bigger
> > > > > >> > gains
> > > > > >> > > > are
> > > > > >> > > > > > >> > probably
> > > > > >> > > > > > >> > > > from
> > > > > >> > > > > > >> > > > > > reducing the number of partitions that
> need
> > > to
> > > > be
> > > > > >> > listed
> > > > > >> > > > > > >> > > individually.
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > > -Jason
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur
> > > Karaman <
> > > > > >> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> > > > > >> > > > > > >> > > > > > wrote:
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > > > When figuring out these optimizations,
> > it's
> > > > > worth
> > > > > >> > > > keeping
> > > > > >> > > > > in
> > > > > >> > > > > > >> mind
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > > > improvements when the message is
> > > uncompressed
> > > > > vs
> > > > > >> > when
> > > > > >> > > > it's
> > > > > >> > > > > > >> > > > compressed.
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > When uncompressed:
> > > > > >> > > > > > >> > > > > > > Fixing the Assignment serialization to
> > > > instead
> > > > > >> be a
> > > > > >> > > > topic
> > > > > >> > > > > > >> index
> > > > > >> > > > > > >> > > into
> > > > > >> > > > > > >> > > > > the
> > > > > >> > > > > > >> > > > > > > corresponding member's subscription
> list
> > > > would
> > > > > >> > usually
> > > > > >> > > > be
> > > > > >> > > > > a
> > > > > >> > > > > > >> good
> > > > > >> > > > > > >> > > > thing.
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > I think the proposal is only worse when
> > the
> > > > > topic
> > > > > >> > > names
> > > > > >> > > > > are
> > > > > >> > > > > > >> > small.
> > > > > >> > > > > > >> > > > The
> > > > > >> > > > > > >> > > > > > > Type.STRING we use in our protocol for
> > the
> > > > > >> > > assignment's
> > > > > >> > > > > > >> > > > TOPIC_KEY_NAME
> > > > > >> > > > > > >> > > > > is
> > > > > >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE,
> so
> > > our
> > > > > >> strings
> > > > > >> > > are
> > > > > >> > > > > > first
> > > > > >> > > > > > >> > > > > prepended
> > > > > >> > > > > > >> > > > > > > with 2 bytes to indicate the string
> size.
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > The new proposal does worse when:
> > > > > >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> > > > > >> > index_type_size
> > > > > >> > > > > > >> > > > > > > in other words when:
> > > > > >> > > > > > >> > > > > > > utf_encoded_string_payload_size <
> > > > > >> index_type_size -
> > > > > >> > 2
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > If the index type ends up being
> > Type.INT32,
> > > > > then
> > > > > >> the
> > > > > >> > > > > > proposal
> > > > > >> > > > > > >> is
> > > > > >> > > > > > >> > > > worse
> > > > > >> > > > > > >> > > > > > when
> > > > > >> > > > > > >> > > > > > > the topic is length 1.
> > > > > >> > > > > > >> > > > > > > If the index type ends up being
> > Type.INT64,
> > > > > then
> > > > > >> the
> > > > > >> > > > > > proposal
> > > > > >> > > > > > >> is
> > > > > >> > > > > > >> > > > worse
> > > > > >> > > > > > >> > > > > > when
> > > > > >> > > > > > >> > > > > > > the topic is less than length 6.
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > When compressed:
> > > > > >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure
> > how
> > > > > >> things
> > > > > >> > > > change
> > > > > >> > > > > > when
> > > > > >> > > > > > >> > > > > > compression
> > > > > >> > > > > > >> > > > > > > comes into the picture. This would be
> > worth
> > > > > >> > > > investigating.
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James
> > > Cheng
> > > > <
> > > > > >> > > > > > >> > wushujames@gmail.com
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > > > wrote:
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
> > > > > >> Gustafson <
> > > > > >> > > > > > >> > > > jason@confluent.io>
> > > > > >> > > > > > >> > > > > > > > wrote:
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to
> lay
> > > out
> > > > > the
> > > > > >> > > > > assignment
> > > > > >> > > > > > >> > without
> > > > > >> > > > > > >> > > > > > needing
> > > > > >> > > > > > >> > > > > > > > to
> > > > > >> > > > > > >> > > > > > > > > explicitly repeat the topic? For
> > > example,
> > > > > the
> > > > > >> > > leader
> > > > > >> > > > > > could
> > > > > >> > > > > > >> > sort
> > > > > >> > > > > > >> > > > the
> > > > > >> > > > > > >> > > > > > > > topics
> > > > > >> > > > > > >> > > > > > > > > for each member and just use an
> > integer
> > > > to
> > > > > >> > > represent
> > > > > >> > > > > the
> > > > > >> > > > > > >> > index
> > > > > >> > > > > > >> > > of
> > > > > >> > > > > > >> > > > > > each
> > > > > >> > > > > > >> > > > > > > > > topic within the sorted list (note
> > this
> > > > > >> depends
> > > > > >> > on
> > > > > >> > > > the
> > > > > >> > > > > > >> > > > subscription
> > > > > >> > > > > > >> > > > > > > > > including the full topic list).
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex
> > [Partition]]
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other
> > > compression)
> > > > > >> > basically
> > > > > >> > > > do
> > > > > >> > > > > > >> this?
> > > > > >> > > > > > >> > If
> > > > > >> > > > > > >> > > > the
> > > > > >> > > > > > >> > > > > > > topic
> > > > > >> > > > > > >> > > > > > > > is a string and the topic is repeated
> > > > > >> throughout,
> > > > > >> > > > won't
> > > > > >> > > > > > >> > > compression
> > > > > >> > > > > > >> > > > > > > > basically replace all repeated
> > instances
> > > of
> > > > > it
> > > > > >> > with
> > > > > >> > > an
> > > > > >> > > > > > index
> > > > > >> > > > > > >> > > > > reference
> > > > > >> > > > > > >> > > > > > to
> > > > > >> > > > > > >> > > > > > > > the full string?
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > > > -James
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > You could even combine these two
> > > options
> > > > so
> > > > > >> that
> > > > > >> > > you
> > > > > >> > > > > > have
> > > > > >> > > > > > >> > only
> > > > > >> > > > > > >> > > 3
> > > > > >> > > > > > >> > > > > > > integers
> > > > > >> > > > > > >> > > > > > > > > for each topic assignment:
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex
> > MinPartition
> > > > > >> > > MaxPartition]
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > There may even be better options
> > with a
> > > > > >> little
> > > > > >> > > more
> > > > > >> > > > > > >> thought.
> > > > > >> > > > > > >> > > All
> > > > > >> > > > > > >> > > > of
> > > > > >> > > > > > >> > > > > > > this
> > > > > >> > > > > > >> > > > > > > > is
> > > > > >> > > > > > >> > > > > > > > > just part of the client-side
> > protocol,
> > > so
> > > > > it
> > > > > >> > > > wouldn't
> > > > > >> > > > > > >> require
> > > > > >> > > > > > >> > > any
> > > > > >> > > > > > >> > > > > > > version
> > > > > >> > > > > > >> > > > > > > > > bumps on the broker. What do you
> > think?
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > Thanks,
> > > > > >> > > > > > >> > > > > > > > > Jason
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM,
> > > Guozhang
> > > > > >> Wang <
> > > > > >> > > > > > >> > > > wangguoz@gmail.com
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > > > > > wrote:
> > > > > >> > > > > > >> > > > > > > > >
> > > > > >> > > > > > >> > > > > > > > >> The original concern is that regex
> > may
> > > > not
> > > > > >> be
> > > > > >> > > > > > efficiently
> > > > > >> > > > > > >> > > > > supported
> > > > > >> > > > > > >> > > > > > > > >> across-languages, but if there is
> a
> > > neat
> > > > > >> > > > workaround I
> > > > > >> > > > > > >> would
> > > > > >> > > > > > >> > > love
> > > > > >> > > > > > >> > > > > to
> > > > > >> > > > > > >> > > > > > > > learn.
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >> Guozhang
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM,
> > > Ismael
> > > > > >> Juma <
> > > > > >> > > > > > >> > > ismael@juma.me.uk
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > > > > > wrote:
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>> Having said that, as a general
> > > point, I
> > > > > >> think
> > > > > >> > we
> > > > > >> > > > > > should
> > > > > >> > > > > > >> > > > consider
> > > > > >> > > > > > >> > > > > > > > >> supporting
> > > > > >> > > > > > >> > > > > > > > >>> topic patterns in the wire
> > protocol.
> > > It
> > > > > >> > requires
> > > > > >> > > > > some
> > > > > >> > > > > > >> > > thinking
> > > > > >> > > > > > >> > > > > for
> > > > > >> > > > > > >> > > > > > > > >>> cross-language support, but it
> > seems
> > > > > >> > > surmountable
> > > > > >> > > > > and
> > > > > >> > > > > > it
> > > > > >> > > > > > >> > > could
> > > > > >> > > > > > >> > > > > make
> > > > > >> > > > > > >> > > > > > > > >> certain
> > > > > >> > > > > > >> > > > > > > > >>> operations a lot more efficient
> > (the
> > > > fact
> > > > > >> > that a
> > > > > >> > > > > basic
> > > > > >> > > > > > >> > regex
> > > > > >> > > > > > >> > > > > > > > subscription
> > > > > >> > > > > > >> > > > > > > > >>> causes the consumer to request
> > > metadata
> > > > > for
> > > > > >> > all
> > > > > >> > > > > topics
> > > > > >> > > > > > >> is
> > > > > >> > > > > > >> > not
> > > > > >> > > > > > >> > > > > > great).
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>> Ismael
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM,
> > > > > Guozhang
> > > > > >> > Wang
> > > > > >> > > <
> > > > > >> > > > > > >> > > > > > wangguoz@gmail.com>
> > > > > >> > > > > > >> > > > > > > > >>> wrote:
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in
> > changing
> > > > the
> > > > > >> > > handling
> > > > > >> > > > > > >> logics of
> > > > > >> > > > > > >> > > > > single
> > > > > >> > > > > > >> > > > > > > > large
> > > > > >> > > > > > >> > > > > > > > >>>> message on the consumer side.
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>> As for the case of "a single
> group
> > > > > >> > subscribing
> > > > > >> > > to
> > > > > >> > > > > > 3000
> > > > > >> > > > > > >> > > > topics",
> > > > > >> > > > > > >> > > > > > with
> > > > > >> > > > > > >> > > > > > > > >> 100
> > > > > >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
> > > > > >> reasonable
> > > > > >> > to
> > > > > >> > > me
> > > > > >> > > > > > (when
> > > > > >> > > > > > >> > > > storing
> > > > > >> > > > > > >> > > > > in
> > > > > >> > > > > > >> > > > > > > ZK,
> > > > > >> > > > > > >> > > > > > > > >> we
> > > > > >> > > > > > >> > > > > > > > >>>> also have the znode limit which
> is
> > > set
> > > > > to
> > > > > >> 1Mb
> > > > > >> > > by
> > > > > >> > > > > > >> default,
> > > > > >> > > > > > >> > > > though
> > > > > >> > > > > > >> > > > > > > > >>> admittedly
> > > > > >> > > > > > >> > > > > > > > >>>> it is only for one consumer).
> And
> > if
> > > > we
> > > > > do
> > > > > >> > the
> > > > > >> > > > > change
> > > > > >> > > > > > >> as
> > > > > >> > > > > > >> > Jun
> > > > > >> > > > > > >> > > > > > > > suggested,
> > > > > >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory
> > pressure
> > > is
> > > > > OK
> > > > > >> I
> > > > > >> > > > think.
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>> Guozhang
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51
> PM,
> > > Onur
> > > > > >> > Karaman
> > > > > >> > > <
> > > > > >> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> > > > > >> > > > > > >> > > > > > > > >>>>> wrote:
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>>> Results without compression:
> > > > > >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the
> > > > tipping
> > > > > >> > point
> > > > > >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>> So it looks like gzip
> compression
> > > > > shrinks
> > > > > >> > the
> > > > > >> > > > > > message
> > > > > >> > > > > > >> > size
> > > > > >> > > > > > >> > > by
> > > > > >> > > > > > >> > > > > 4x.
> > > > > >> > > > > > >> > > > > > > > >>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47
> AM,
> > > Jun
> > > > > Rao
> > > > > >> <
> > > > > >> > > > > > >> > jun@confluent.io
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > > > > > wrote:
> > > > > >> > > > > > >> > > > > > > > >>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>> Onur,
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix
> > how
> > > we
> > > > > >> deal
> > > > > >> > > with
> > > > > >> > > > > the
> > > > > >> > > > > > >> case
> > > > > >> > > > > > >> > > > when a
> > > > > >> > > > > > >> > > > > > > > >>> message
> > > > > >> > > > > > >> > > > > > > > >>>> is
> > > > > >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size.
> > Today,
> > > > if
> > > > > >> the
> > > > > >> > > fetch
> > > > > >> > > > > > size
> > > > > >> > > > > > >> is
> > > > > >> > > > > > >> > > > > smaller
> > > > > >> > > > > > >> > > > > > > > >> than
> > > > > >> > > > > > >> > > > > > > > >>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will
> > get
> > > > > stuck.
> > > > > >> > > > Instead,
> > > > > >> > > > > > we
> > > > > >> > > > > > >> can
> > > > > >> > > > > > >> > > > > simply
> > > > > >> > > > > > >> > > > > > > > >>> return
> > > > > >> > > > > > >> > > > > > > > >>>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>> full message if it's larger
> than
> > > the
> > > > > >> fetch
> > > > > >> > > size
> > > > > >> > > > > w/o
> > > > > >> > > > > > >> > > > requiring
> > > > > >> > > > > > >> > > > > > the
> > > > > >> > > > > > >> > > > > > > > >>>>> consumer
> > > > > >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch
> > size.
> > > > On
> > > > > >> the
> > > > > >> > > > broker
> > > > > >> > > > > > >> side,
> > > > > >> > > > > > >> > to
> > > > > >> > > > > > >> > > > > serve
> > > > > >> > > > > > >> > > > > > a
> > > > > >> > > > > > >> > > > > > > > >>> fetch
> > > > > >> > > > > > >> > > > > > > > >>>>>> request, we already do an
> index
> > > > lookup
> > > > > >> and
> > > > > >> > > then
> > > > > >> > > > > > scan
> > > > > >> > > > > > >> the
> > > > > >> > > > > > >> > > > log a
> > > > > >> > > > > > >> > > > > > bit
> > > > > >> > > > > > >> > > > > > > > >> to
> > > > > >> > > > > > >> > > > > > > > >>>>> find
> > > > > >> > > > > > >> > > > > > > > >>>>>> the message with the requested
> > > > offset.
> > > > > >> We
> > > > > >> > can
> > > > > >> > > > > just
> > > > > >> > > > > > >> check
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > > size
> > > > > >> > > > > > >> > > > > > > > >> of
> > > > > >> > > > > > >> > > > > > > > >>>> that
> > > > > >> > > > > > >> > > > > > > > >>>>>> message and return the full
> > > message
> > > > if
> > > > > >> its
> > > > > >> > > size
> > > > > >> > > > > is
> > > > > >> > > > > > >> > larger
> > > > > >> > > > > > >> > > > than
> > > > > >> > > > > > >> > > > > > the
> > > > > >> > > > > > >> > > > > > > > >>>> fetch
> > > > > >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is
> > > really
> > > > > for
> > > > > >> > > > > > performance
> > > > > >> > > > > > >> > > > > > optimization,
> > > > > >> > > > > > >> > > > > > > > >>> i.e.
> > > > > >> > > > > > >> > > > > > > > >>>>> in
> > > > > >> > > > > > >> > > > > > > > >>>>>> the common case, we will not
> > > return
> > > > > more
> > > > > >> > > bytes
> > > > > >> > > > > than
> > > > > >> > > > > > >> > fetch
> > > > > >> > > > > > >> > > > > size,
> > > > > >> > > > > > >> > > > > > > but
> > > > > >> > > > > > >> > > > > > > > >>> if
> > > > > >> > > > > > >> > > > > > > > >>>>>> there is a large message, we
> > will
> > > > > return
> > > > > >> > more
> > > > > >> > > > > bytes
> > > > > >> > > > > > >> than
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > > > > >>> specified
> > > > > >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large
> > > > > messages
> > > > > >> are
> > > > > >> > > > rare.
> > > > > >> > > > > > >> So, it
> > > > > >> > > > > > >> > > > > > shouldn't
> > > > > >> > > > > > >> > > > > > > > >>>>> increase
> > > > > >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the
> > > client
> > > > > too
> > > > > >> > > much.
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>> Jun
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34
> AM,
> > > > Onur
> > > > > >> > > Karaman <
> > > > > >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> > > > > >> > > > > > >> > > > > > > > >>>>>> wrote:
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started
> > doing
> > > > some
> > > > > >> > tests
> > > > > >> > > on
> > > > > >> > > > > the
> > > > > >> > > > > > >> new
> > > > > >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> > > > > >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle
> more
> > > > > >> strenuous
> > > > > >> > use
> > > > > >> > > > > cases
> > > > > >> > > > > > >> like
> > > > > >> > > > > > >> > > > > > mirroring
> > > > > >> > > > > > >> > > > > > > > >>>>>> clusters
> > > > > >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and
> > > > thought
> > > > > >> I'd
> > > > > >> > > share
> > > > > >> > > > > > >> > whatever I
> > > > > >> > > > > > >> > > > > have
> > > > > >> > > > > > >> > > > > > so
> > > > > >> > > > > > >> > > > > > > > >>>> far.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the
> > amount
> > > > of
> > > > > >> group
> > > > > >> > > > > > metadata
> > > > > >> > > > > > >> we
> > > > > >> > > > > > >> > > can
> > > > > >> > > > > > >> > > > > fit
> > > > > >> > > > > > >> > > > > > > > >> into
> > > > > >> > > > > > >> > > > > > > > >>>> one
> > > > > >> > > > > > >> > > > > > > > >>>>>>> message
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Some background:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is
> > > > implemented
> > > > > >> in
> > > > > >> > two
> > > > > >> > > > > > phases
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase
> > > that
> > > > > >> > > identifies
> > > > > >> > > > > > >> members
> > > > > >> > > > > > >> > of
> > > > > >> > > > > > >> > > > the
> > > > > >> > > > > > >> > > > > > > > >> group
> > > > > >> > > > > > >> > > > > > > > >>>> and
> > > > > >> > > > > > >> > > > > > > > >>>>>>> aggregates member
> > subscriptions.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that
> > > waits
> > > > > for
> > > > > >> > the
> > > > > >> > > > > group
> > > > > >> > > > > > >> > leader
> > > > > >> > > > > > >> > > to
> > > > > >> > > > > > >> > > > > > > > >> decide
> > > > > >> > > > > > >> > > > > > > > >>>>> member
> > > > > >> > > > > > >> > > > > > > > >>>>>>> assignments based on the
> member
> > > > > >> > > subscriptions
> > > > > >> > > > > > across
> > > > > >> > > > > > >> > the
> > > > > >> > > > > > >> > > > > group.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this
> > > > decision
> > > > > >> > with a
> > > > > >> > > > > > >> > > > > SyncGroupRequest.
> > > > > >> > > > > > >> > > > > > > > >> The
> > > > > >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> > > > > >> SyncGroupRequests
> > > > > >> > > by
> > > > > >> > > > > > >> appending
> > > > > >> > > > > > >> > > all
> > > > > >> > > > > > >> > > > > > group
> > > > > >> > > > > > >> > > > > > > > >>>> state
> > > > > >> > > > > > >> > > > > > > > >>>>>>> into a single message under
> the
> > > > > >> > > > > __consumer_offsets
> > > > > >> > > > > > >> > topic.
> > > > > >> > > > > > >> > > > > This
> > > > > >> > > > > > >> > > > > > > > >>>> message
> > > > > >> > > > > > >> > > > > > > > >>>>> is
> > > > > >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and
> > > contains
> > > > > each
> > > > > >> > > member
> > > > > >> > > > > > >> > > subscription
> > > > > >> > > > > > >> > > > > as
> > > > > >> > > > > > >> > > > > > > > >> well
> > > > > >> > > > > > >> > > > > > > > >>>> as
> > > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each
> > > member.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> The environment:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - one broker
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets
> > > partition
> > > > > >> > > > > > >> > > > > > > > >>>>>>> -
> > > offsets.topic.compression.codec=1
> > > > > //
> > > > > >> > this
> > > > > >> > > is
> > > > > >> > > > > > gzip
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending
> > > KAFKA-3718
> > > > > >> patch
> > > > > >> > > that
> > > > > >> > > > > > >> actually
> > > > > >> > > > > > >> > > > makes
> > > > > >> > > > > > >> > > > > > use
> > > > > >> > > > > > >> > > > > > > > >> of
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > offsets.topic.compression.codec:
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> https://github.com/apache/kafka/pull/1394
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is
> > an
> > > > > actual
> > > > > >> > > subset
> > > > > >> > > > > of
> > > > > >> > > > > > >> > topics
> > > > > >> > > > > > >> > > > from
> > > > > >> > > > > > >> > > > > > one
> > > > > >> > > > > > >> > > > > > > > >>> of
> > > > > >> > > > > > >> > > > > > > > >>>>> our
> > > > > >> > > > > > >> > > > > > > > >>>>>>> clusters.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters
> long
> > > on
> > > > > >> average
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying
> > number
> > > > of
> > > > > >> > > consumers
> > > > > >> > > > > > each
> > > > > >> > > > > > >> > > > hardcoded
> > > > > >> > > > > > >> > > > > > > > >> with
> > > > > >> > > > > > >> > > > > > > > >>>> all
> > > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests
> > > more
> > > > > >> > > consistent.
> > > > > >> > > > > > >> > > wildcarding
> > > > > >> > > > > > >> > > > > with
> > > > > >> > > > > > >> > > > > > > > >> .*
> > > > > >> > > > > > >> > > > > > > > >>>>> should
> > > > > >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> > > > > >> subscription
> > > > > >> > > > hits
> > > > > >> > > > > > the
> > > > > >> > > > > > >> > > > > coordinator
> > > > > >> > > > > > >> > > > > > > > >> as
> > > > > >> > > > > > >> > > > > > > > >>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>>> subscription has already been
> > > fully
> > > > > >> > expanded
> > > > > >> > > > out
> > > > > >> > > > > > to
> > > > > >> > > > > > >> the
> > > > > >> > > > > > >> > > > list
> > > > > >> > > > > > >> > > > > of
> > > > > >> > > > > > >> > > > > > > > >>>> topics
> > > > > >> > > > > > >> > > > > > > > >>>>> by
> > > > > >> > > > > > >> > > > > > > > >>>>>>> the consumers.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages
> to
> > > > > >> Log.scala
> > > > > >> > to
> > > > > >> > > > > print
> > > > > >> > > > > > >> out
> > > > > >> > > > > > >> > the
> > > > > >> > > > > > >> > > > > > message
> > > > > >> > > > > > >> > > > > > > > >>>> sizes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> after compression
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at
> all
> > > and
> > > > > >> auto
> > > > > >> > > > commits
> > > > > >> > > > > > are
> > > > > >> > > > > > >> > > > > disabled.
> > > > > >> > > > > > >> > > > > > > > >> The
> > > > > >> > > > > > >> > > > > > > > >>>> only
> > > > > >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting
> > added
> > > > is
> > > > > >> the
> > > > > >> > > > > > >> > > __consumer_offsets
> > > > > >> > > > > > >> > > > > > topic
> > > > > >> > > > > > >> > > > > > > > >>> and
> > > > > >> > > > > > >> > > > > > > > >>>>>>> they're only from storing
> group
> > > > > >> metadata
> > > > > >> > > while
> > > > > >> > > > > > >> > processing
> > > > > >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Results:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> The results below show that
> we
> > > > exceed
> > > > > >> the
> > > > > >> > > > > 1000012
> > > > > >> > > > > > >> byte
> > > > > >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes
> > limit
> > > > > >> > relatively
> > > > > >> > > > > > quickly
> > > > > >> > > > > > >> > > > (between
> > > > > >> > > > > > >> > > > > > > > >> 30-40
> > > > > >> > > > > > >> > > > > > > > >>>>>>> consumers):
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes *
> > the
> > > > > >> tipping
> > > > > >> > > point
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself
> is
> > > > pretty
> > > > > >> > > gradual.
> > > > > >> > > > > > >> Plotting
> > > > > >> > > > > > >> > > the
> > > > > >> > > > > > >> > > > > > > > >> points
> > > > > >> > > > > > >> > > > > > > > >>>>> makes
> > > > > >> > > > > > >> > > > > > > > >>>>>> it
> > > > > >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the
> > > > number
> > > > > of
> > > > > >> > > > > consumers:
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >>
> > > > > >> > > > > >
> > > > > >> > > > >
> > > > > >> > > >
> > > > > >> > >
> > > > > >> >
> > > > > >>
> > > > >
> > > >
> > >
> >
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers
> > > aren't
> > > > > >> > averages
> > > > > >> > > > or
> > > > > >> > > > > > >> medians
> > > > > >> > > > > > >> > > or
> > > > > >> > > > > > >> > > > > > > > >> anything
> > > > > >> > > > > > >> > > > > > > > >>>>> like
> > > > > >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size
> > > from
> > > > a
> > > > > >> given
> > > > > >> > > > run.
> > > > > >> > > > > I
> > > > > >> > > > > > >> did
> > > > > >> > > > > > >> > run
> > > > > >> > > > > > >> > > > > them
> > > > > >> > > > > > >> > > > > > a
> > > > > >> > > > > > >> > > > > > > > >>> few
> > > > > >> > > > > > >> > > > > > > > >>>>>> times
> > > > > >> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Impact:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> > > > > >> > > > __consumer_offsets
> > > > > >> > > > > > >> topic
> > > > > >> > > > > > >> > > with
> > > > > >> > > > > > >> > > > > my
> > > > > >> > > > > > >> > > > > > > > >>>> pending
> > > > > >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the
> > > AwaitingSync
> > > > > >> phase
> > > > > >> > of
> > > > > >> > > > the
> > > > > >> > > > > > >> group
> > > > > >> > > > > > >> > > fails
> > > > > >> > > > > > >> > > > > > with
> > > > > >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This
> > > means
> > > > > the
> > > > > >> > > > combined
> > > > > >> > > > > > >> size
> > > > > >> > > > > > >> > of
> > > > > >> > > > > > >> > > > each
> > > > > >> > > > > > >> > > > > > > > >>>> member's
> > > > > >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments
> > > > > exceeded
> > > > > >> the
> > > > > >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> > > > > >> > > > > > >> > > > > > > > >>>>> of
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends
> > up
> > > > > dying.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Options:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the
> > > number
> > > > > of
> > > > > >> > > > consumers
> > > > > >> > > > > > in
> > > > > >> > > > > > >> the
> > > > > >> > > > > > >> > > > > group.
> > > > > >> > > > > > >> > > > > > > > >> This
> > > > > >> > > > > > >> > > > > > > > >>>>> isn't
> > > > > >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in
> > more
> > > > > >> > strenuous
> > > > > >> > > > use
> > > > > >> > > > > > >> cases
> > > > > >> > > > > > >> > > like
> > > > > >> > > > > > >> > > > > > > > >>>> MirrorMaker
> > > > > >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the
> > group
> > > > > into
> > > > > >> > > smaller
> > > > > >> > > > > > >> groups
> > > > > >> > > > > > >> > > which
> > > > > >> > > > > > >> > > > > > > > >>> together
> > > > > >> > > > > > >> > > > > > > > >>>>> will
> > > > > >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the
> > topics.
> > > > This
> > > > > >> > gives
> > > > > >> > > > each
> > > > > >> > > > > > >> group
> > > > > >> > > > > > >> > > > > member a
> > > > > >> > > > > > >> > > > > > > > >>>> smaller
> > > > > >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has
> topics
> > > > > >> starting
> > > > > >> > > with
> > > > > >> > > > > a-m
> > > > > >> > > > > > >> while
> > > > > >> > > > > > >> > > g2
> > > > > >> > > > > > >> > > > > has
> > > > > >> > > > > > >> > > > > > > > >>> topics
> > > > > >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would
> > be
> > > > > >> > > operationally
> > > > > >> > > > > > >> painful
> > > > > >> > > > > > >> > to
> > > > > >> > > > > > >> > > > > > manage.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the
> > > topics
> > > > > >> among
> > > > > >> > > > members
> > > > > >> > > > > > of
> > > > > >> > > > > > >> the
> > > > > >> > > > > > >> > > > > group.
> > > > > >> > > > > > >> > > > > > > > >>> Again
> > > > > >> > > > > > >> > > > > > > > >>>>> this
> > > > > >> > > > > > >> > > > > > > > >>>>>>> gives each group member a
> > smaller
> > > > > >> > > > subscription.
> > > > > >> > > > > > This
> > > > > >> > > > > > >> > > would
> > > > > >> > > > > > >> > > > > also
> > > > > >> > > > > > >> > > > > > > > >> be
> > > > > >> > > > > > >> > > > > > > > >>>>>>> operationally painful to
> > manage.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> > > > > >> > > > > > >> KafkaConfig.messageMaxBytes
> > > > > >> > > > > > >> > (a
> > > > > >> > > > > > >> > > > > > > > >>> topic-level
> > > > > >> > > > > > >> > > > > > > > >>>>>>> config) and
> > > > > >> > KafkaConfig.replicaFetchMaxBytes
> > > > > >> > > > (a
> > > > > >> > > > > > >> > > > broker-level
> > > > > >> > > > > > >> > > > > > > > >>> config).
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to
> > just
> > > > the
> > > > > >> > > > > > >> __consumer_offsets
> > > > > >> > > > > > >> > > > topic
> > > > > >> > > > > > >> > > > > > > > >> seems
> > > > > >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but
> > bumping
> > > up
> > > > > the
> > > > > >> > > > > > broker-level
> > > > > >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> > > > > >> > > > > > >> > > > > > > > >>>>>>> would probably need more
> > > attention.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try
> different
> > > > > >> > compression
> > > > > >> > > > > > codecs.
> > > > > >> > > > > > >> > Based
> > > > > >> > > > > > >> > > > on
> > > > > >> > > > > > >> > > > > 2
> > > > > >> > > > > > >> > > > > > > > >>>> minutes
> > > > > >> > > > > > >> > > > > > > > >>>>> of
> > > > > >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4
> and
> > > > > snappy
> > > > > >> are
> > > > > >> > > > > faster
> > > > > >> > > > > > >> than
> > > > > >> > > > > > >> > > gzip
> > > > > >> > > > > > >> > > > > but
> > > > > >> > > > > > >> > > > > > > > >>> have
> > > > > >> > > > > > >> > > > > > > > >>>>>> worse
> > > > > >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably
> > > won't
> > > > > >> help.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change:
> > support
> > > > > >> sending
> > > > > >> > > the
> > > > > >> > > > > > regex
> > > > > >> > > > > > >> > over
> > > > > >> > > > > > >> > > > the
> > > > > >> > > > > > >> > > > > > wire
> > > > > >> > > > > > >> > > > > > > > >>>>> instead
> > > > > >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> > > > > >> > subscriptions. I
> > > > > >> > > > > think
> > > > > >> > > > > > >> > people
> > > > > >> > > > > > >> > > > > said
> > > > > >> > > > > > >> > > > > > in
> > > > > >> > > > > > >> > > > > > > > >>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>> past
> > > > > >> > > > > > >> > > > > > > > >>>>>>> that different languages have
> > > > subtle
> > > > > >> > > > differences
> > > > > >> > > > > > in
> > > > > >> > > > > > >> > > regex,
> > > > > >> > > > > > >> > > > so
> > > > > >> > > > > > >> > > > > > > > >> this
> > > > > >> > > > > > >> > > > > > > > >>>>>> doesn't
> > > > > >> > > > > > >> > > > > > > > >>>>>>> play nicely with
> cross-language
> > > > > groups.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change:
> maybe
> > > we
> > > > > can
> > > > > >> > > reverse
> > > > > >> > > > > the
> > > > > >> > > > > > >> > > mapping?
> > > > > >> > > > > > >> > > > > > > > >> Instead
> > > > > >> > > > > > >> > > > > > > > >>>> of
> > > > > >> > > > > > >> > > > > > > > >>>>>>> mapping from member to
> > > > subscriptions,
> > > > > >> we
> > > > > >> > can
> > > > > >> > > > > map a
> > > > > >> > > > > > >> > > > > subscription
> > > > > >> > > > > > >> > > > > > > > >> to
> > > > > >> > > > > > >> > > > > > > > >>> a
> > > > > >> > > > > > >> > > > > > > > >>>>> list
> > > > > >> > > > > > >> > > > > > > > >>>>>>> of members.
> > > > > >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change:
> maybe
> > > we
> > > > > can
> > > > > >> try
> > > > > >> > > to
> > > > > >> > > > > > break
> > > > > >> > > > > > >> > apart
> > > > > >> > > > > > >> > > > the
> > > > > >> > > > > > >> > > > > > > > >>>>>> subscription
> > > > > >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> > > > > >> > > SyncGroupRequest
> > > > > >> > > > > > into
> > > > > >> > > > > > >> > > > multiple
> > > > > >> > > > > > >> > > > > > > > >>> records?
> > > > > >> > > > > > >> > > > > > > > >>>>>> They
> > > > > >> > > > > > >> > > > > > > > >>>>>>> can still go to the same
> > message
> > > > set
> > > > > >> and
> > > > > >> > get
> > > > > >> > > > > > >> appended
> > > > > >> > > > > > >> > > > > together.
> > > > > >> > > > > > >> > > > > > > > >>> This
> > > > > >> > > > > > >> > > > > > > > >>>>> way
> > > > > >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment
> > > size,
> > > > > >> which
> > > > > >> > > > > shouldn't
> > > > > >> > > > > > >> be a
> > > > > >> > > > > > >> > > > > > problem.
> > > > > >> > > > > > >> > > > > > > > >>> This
> > > > > >> > > > > > >> > > > > > > > >>>>> can
> > > > > >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right
> because
> > > > we're
> > > > > >> > > currently
> > > > > >> > > > > > >> keying
> > > > > >> > > > > > >> > > these
> > > > > >> > > > > > >> > > > > > > > >>> messages
> > > > > >> > > > > > >> > > > > > > > >>>> on
> > > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > > >> > > > > > >> > > > > > > > >>>>>>> group, so I think records
> from
> > > the
> > > > > same
> > > > > >> > > > > rebalance
> > > > > >> > > > > > >> might
> > > > > >> > > > > > >> > > > > > > > >>> accidentally
> > > > > >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> > > > > >> understanding
> > > > > >> > of
> > > > > >> > > > > > >> compaction
> > > > > >> > > > > > >> > > > isn't
> > > > > >> > > > > > >> > > > > > > > >> that
> > > > > >> > > > > > >> > > > > > > > >>>>> great.
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> Todo:
> > > > > >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to
> > rerun
> > > > the
> > > > > >> tests
> > > > > >> > > > with
> > > > > >> > > > > no
> > > > > >> > > > > > >> > > > > compression
> > > > > >> > > > > > >> > > > > > > > >> just
> > > > > >> > > > > > >> > > > > > > > >>>> to
> > > > > >> > > > > > >> > > > > > > > >>>>>> see
> > > > > >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but
> > it's
> > > > > >> getting
> > > > > >> > > > late.
> > > > > >> > > > > > >> Maybe
> > > > > >> > > > > > >> > > > > tomorrow?
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>> - Onur
> > > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>> --
> > > > > >> > > > > > >> > > > > > > > >>>> -- Guozhang
> > > > > >> > > > > > >> > > > > > > > >>>>
> > > > > >> > > > > > >> > > > > > > > >>>
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > > >> --
> > > > > >> > > > > > >> > > > > > > > >> -- Guozhang
> > > > > >> > > > > > >> > > > > > > > >>
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > > >
> > > > > >> > > > > > >> > > > > > >
> > > > > >> > > > > > >> > > > > >
> > > > > >> > > > > > >> > > > >
> > > > > >> > > > > > >> > > >
> > > > > >> > > > > > >> > >
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >> > --
> > > > > >> > > > > > >> > -- Guozhang
> > > > > >> > > > > > >> >
> > > > > >> > > > > > >>
> > > > > >> > > > > > >
> > > > > >> > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > >
> > > > > >> > > >
> > > > > >> > >
> > > > > >> >
> > > > > >>
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Becket Qin <be...@gmail.com>]

Hi Jason,

I am trying to understand the gain of saving the assignment and metadata in
a topic and return the offsets to the consumers. This obviously saves
memory footprint as we agreed before. But does it save network bandwidth?
The consumers still need to read the same amount of data from the
coordinator broker, right?

In terms of the current proposal, Onur and I discussed offline. It looks
that having a separate "offset.replica.fetch.max.bytes" does not buy us
much. Users are likely setting it to be the same value as the max message
size of the __consumer_offsets topic. The reason is this configuration is
mainly for consumer side memory management, the users would not want to set
it to be bigger than necessary.

The solution we discussed is what Jun suggested, i.e. look at the size of
the first message returned. If the size of the message is greater than the
fetch max bytes, we always return the first message even it is bigger than
max fetch size. Otherwise we only return up to fetch max bytes. We only do
this for __consumer_offsets topic so no user topic will be impacted.

Thanks,

Jiangjie (Becket) Qin

On Thu, Jun 9, 2016 at 2:40 PM, Jason Gustafson <ja...@confluent.io> wrote:

> Hi Onur,
>
> I didn't have a specific proposal in mind, I was just thinking analogously
> with how Connect ensures task configurations are propagated to tasks
> consistently when it rebalances the cluster. The high level concept is to
> take the assignment data out of the rebalance protocol itself and replace
> it with a pointer. For example, the pointer can be a (topic, partition,
> offset) tuple which can be fetched separately by the consumer instance
> after the rebalance completes. Then the leader would generate the
> assignments, write them to Kafka, and send the pointers to the rest of the
> group in the SyncGroup. This is more or less how Connect works.
>
> -Jason
>
> On Thu, Jun 9, 2016 at 11:10 AM, Onur Karaman
> <okaraman@linkedin.com.invalid
> > wrote:
>
> > I think the value of adding a "offsets.replica.fetch.max.bytes" config is
> > that we don't break/change the meaning of "replica.fetch.max.bytes".
> >
> > We can also set "offsets.replica.fetch.max.bytes" to be a value safely
> > larger than what we expect to ever allow the __consumer_offsets topic max
> > message size to be without doing the larger change of bumping up the
> global
> > "replica.fetch.max.bytes".
> >
> > On Thu, Jun 9, 2016 at 10:40 AM, Becket Qin <be...@gmail.com>
> wrote:
> >
> > > I think taking bigger one of the fetch size and message size limit is
> > > probably good enough. If we have a separate
> > > "offset.replica.fetch.max.bytes", I guess the value will always be set
> to
> > > max message size of the __consumer_offsets topic, which does not seem
> to
> > > have much value.
> > >
> > > On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman
> > <okaraman@linkedin.com.invalid
> > > >
> > > wrote:
> > >
> > > > Maybe another approach can be to add a new
> > > > "offsets.replica.fetch.max.bytes" config on the brokers.
> > > >
> > > > On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <ok...@linkedin.com>
> > > > wrote:
> > > >
> > > > > I made a PR with a tweak to Jun's/Becket's proposal:
> > > > > https://github.com/apache/kafka/pull/1484
> > > > >
> > > > > It just tweaks the fetch behavior specifically for replicas
> fetching
> > > from
> > > > > the __consumer_offsets topic when the fetcher's
> > > "replica.fetch.max.bytes"
> > > > > is less than the __consumer_offset leader's "message.max.bytes" to
> > take
> > > > the
> > > > > max of the two.
> > > > >
> > > > > I'm honestly not that happy with this solution, as I'd rather not
> > > change
> > > > > the "replica.fetch.max.bytes" config from being a limit to a
> > > > > recommendation. I'd definitely be happy to hear other alternatives!
> > > > >
> > > > > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> > > > > onurkaraman.apache@gmail.com> wrote:
> > > > >
> > > > >> Sorry I know next to nothing about Kafka Connect. I didn't
> > understand
> > > > the
> > > > >> Kafka Connect / MM idea you brought up. Can you go into more
> detail?
> > > > >>
> > > > >> Otherwise I think our remaining options are:
> > > > >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
> > > > >> __consumer_offsets topic and change the fetch behavior when
> message
> > > size
> > > > >> is
> > > > >> larger than fetch size
> > > > >> - option 6: support sending the regex over the wire instead of the
> > > fully
> > > > >> expanded topic subscriptions. This should cut down the message
> size
> > > from
> > > > >> the subscription side. Again this only helps when pattern-based
> > > > >> subscriptions are done.
> > > > >>
> > > > >> minor correction to an earlier comment I made regarding the
> message
> > > > size:
> > > > >> message size ~ sum(s_i + a_i for i in range [1, |C|])
> > > > >>
> > > > >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <
> > jason@confluent.io>
> > > > >> wrote:
> > > > >>
> > > > >> > Hey Onur,
> > > > >> >
> > > > >> > Thanks for the investigation. It seems the conclusion is that
> the
> > > > >> compact
> > > > >> > format helps, but perhaps not enough to justify adding a new
> > > > assignment
> > > > >> > schema? I'm not sure there's much more room for savings unless
> we
> > > > change
> > > > >> > something more fundamental in the assignment approach. We spent
> > some
> > > > >> time
> > > > >> > thinking before about whether we could let the consumers compute
> > > their
> > > > >> > assignment locally from a smaller set of information, but the
> > > > difficulty
> > > > >> > (I'm sure you remember) is reaching consensus on topic metadata.
> > > Kafka
> > > > >> > Connect has a similar problem where all the workers need to
> agree
> > on
> > > > >> > connector configurations. Since all configs are stored in a
> single
> > > > topic
> > > > >> > partition, the approach we take there is to propagate the offset
> > in
> > > > the
> > > > >> > assignment protocol. Not sure if we could do something similar
> for
> > > > MM...
> > > > >> > Anyway, it seems like the best workaround at the moment is Jun's
> > > > initial
> > > > >> > suggestion. What do you think?
> > > > >> >
> > > > >> > -Jason
> > > > >> >
> > > > >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> > > > >> > onurkaraman.apache@gmail.com
> > > > >> > > wrote:
> > > > >> >
> > > > >> > > I gave the topic index assignment trick a try against the same
> > > > >> > environment.
> > > > >> > > The implementation just changed the assignment serialization
> and
> > > > >> > > deserialization logic. It didn't change SyncGroupResponse,
> > meaning
> > > > it
> > > > >> > > continues to exclude the subscription from the
> SyncGroupResponse
> > > and
> > > > >> > > assumes the member has kept track of its last subscription.
> > > > >> > >
> > > > >> > > Assignment topic indexing with compression:
> > > > >> > > 1 consumer 34346 bytes
> > > > >> > > 5 consumers 177687 bytes
> > > > >> > > 10 consumers 331897 bytes
> > > > >> > > 20 consumers 572467 bytes
> > > > >> > > 30 consumers 811269 bytes
> > > > >> > > 40 consumers 1047188 bytes * the tipping point
> > > > >> > > 50 consumers 1290092 bytes
> > > > >> > > 60 consumers 1527806 bytes
> > > > >> > > 70 consumers 1769259 bytes
> > > > >> > > 80 consumers 2000118 bytes
> > > > >> > > 90 consumers 2244392 bytes
> > > > >> > > 100 consumers 2482415 bytes
> > > > >> > >
> > > > >> > > Assignment topic indexing without compression:
> > > > >> > > 1 consumer 211904 bytes
> > > > >> > > 5 consumers 677184 bytes
> > > > >> > > 10 consumers 1211154 bytes * the tipping point
> > > > >> > > 20 consumers 2136196 bytes
> > > > >> > > 30 consumers 3061238 bytes
> > > > >> > > 40 consumers 3986280 bytes
> > > > >> > > 50 consumers 4911322 bytes
> > > > >> > > 60 consumers 5836284 bytes
> > > > >> > > 70 consumers 6761246 bytes
> > > > >> > > 80 consumers 7686208 bytes
> > > > >> > > 90 consumers 8611170 bytes
> > > > >> > > 100 consumers 9536132 bytes
> > > > >> > >
> > > > >> > > Assignment topic indexing seems to reduce the size by 500KB
> > > without
> > > > >> > > compression and 80KB with compression. So assignment topic
> > > indexing
> > > > >> makes
> > > > >> > > some difference in both with and without compression but in
> our
> > > case
> > > > >> was
> > > > >> > > not nearly enough.
> > > > >> > >
> > > > >> > > This can be explained by the fact that we aren't actually
> > hitting
> > > > the
> > > > >> > worst
> > > > >> > > case scenario of each consumer being assigned a partition from
> > > every
> > > > >> > topic.
> > > > >> > > The reason is simple: a topic can only fully span all the
> > > consumers
> > > > >> if it
> > > > >> > > has at least as many partitions as there are consumers. Given
> > that
> > > > >> there
> > > > >> > > are 8 partitions per topic and we have 100 consumers, it makes
> > > sense
> > > > >> that
> > > > >> > > we aren't close to this worse case scenario where topic
> indexing
> > > > would
> > > > >> > make
> > > > >> > > a bigger difference.
> > > > >> > >
> > > > >> > > I tweaked the group leader's assignment code to print out the
> > > > >> assignments
> > > > >> > > and found that each consumer was getting either 238 or 239
> > > > partitions.
> > > > >> > Each
> > > > >> > > of these partitions were from unique topics. So the consumers
> > were
> > > > >> really
> > > > >> > > getting partitions from 239 topics instead of the full worst
> > case
> > > > >> > scenario
> > > > >> > > of 3000 topics.
> > > > >> > >
> > > > >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <
> > > > jason@confluent.io>
> > > > >> > > wrote:
> > > > >> > >
> > > > >> > > > Gwen, Joel:
> > > > >> > > >
> > > > >> > > > That's correct. The protocol does allow us to give an
> assignor
> > > its
> > > > >> own
> > > > >> > > > assignment schema, but I think this will require a couple
> > > internal
> > > > >> > > changes
> > > > >> > > > to the consumer to make use of the full generality.
> > > > >> > > >
> > > > >> > > > One thing I'm a little uncertain about is whether we should
> > use
> > > a
> > > > >> > > different
> > > > >> > > > protocol type. For a little context, the group membership
> > > protocol
> > > > >> > allows
> > > > >> > > > the client to provide a "protocol type" when joining the
> group
> > > to
> > > > >> > ensure
> > > > >> > > > that all members have some basic semantic compatibility. For
> > > > >> example,
> > > > >> > the
> > > > >> > > > consumer uses "consumer" and Kafka Connect uses "connect."
> > > > Currently
> > > > >> > all
> > > > >> > > > assignors using the "consumer" protocol share a common
> schema
> > > for
> > > > >> > > > representing subscriptions and assignment. This is
> convenient
> > > for
> > > > >> tools
> > > > >> > > > (like consumer-groups.sh) since they just need to know how
> to
> > > > parse
> > > > >> the
> > > > >> > > > "consumer" protocol type without knowing anything about the
> > > > >> assignors.
> > > > >> > So
> > > > >> > > > introducing another schema would break that assumption and
> > we'd
> > > > need
> > > > >> > > those
> > > > >> > > > tools to do assignor-specific parsing. Maybe this is OK?
> > > > >> Alternatively,
> > > > >> > > we
> > > > >> > > > could use a separate protocol type (e.g.
> "compact-consumer"),
> > > but
> > > > >> that
> > > > >> > > > seems less than desirable.
> > > > >> > > >
> > > > >> > > > Thanks,
> > > > >> > > > Jason
> > > > >> > > >
> > > > >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <
> > > gwen@confluent.io
> > > > >
> > > > >> > > wrote:
> > > > >> > > >
> > > > >> > > > > ah, right - we can add as many strategies as we want.
> > > > >> > > > >
> > > > >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <
> > > > jjkoshy.w@gmail.com
> > > > >> >
> > > > >> > > > wrote:
> > > > >> > > > >
> > > > >> > > > > > > Yes it would be a protocol bump.
> > > > >> > > > > > >
> > > > >> > > > > >
> > > > >> > > > > > Sorry - I'm officially confused. I think it may not be
> > > > required
> > > > >> -
> > > > >> > > since
> > > > >> > > > > the
> > > > >> > > > > > more compact format would be associated with a new
> > > assignment
> > > > >> > > strategy
> > > > >> > > > -
> > > > >> > > > > > right?
> > > > >> > > > > >
> > > > >> > > > > >
> > > > >> > > > > > > smaller than the plaintext PAL, but the
> post-compressed
> > > > binary
> > > > >> > PAL
> > > > >> > > is
> > > > >> > > > > > just
> > > > >> > > > > > > 25% smaller than the post-compressed plaintext PAL.
> IOW
> > > > using
> > > > >> a
> > > > >> > > > symbol
> > > > >> > > > > > > table helps a lot but further compression on that
> > already
> > > > >> compact
> > > > >> > > > > format
> > > > >> > > > > > > would yield only marginal return.
> > > > >> > > > > > >
> > > > >> > > > > >
> > > > >> > > > > > > So basically I feel we could get pretty far with a
> more
> > > > >> compact
> > > > >> > > field
> > > > >> > > > > > > format for assignment and if we do that then we would
> > > > >> potentially
> > > > >> > > not
> > > > >> > > > > > even
> > > > >> > > > > > > want to do any compression.
> > > > >> > > > > > >
> > > > >> > > > > >
> > > > >> > > > > > Also just wanted to add that this compression on the
> > binary
> > > > PAL
> > > > >> did
> > > > >> > > > help
> > > > >> > > > > > but the compression ratio was obviously not as high as
> > > > plaintext
> > > > >> > > > > > compression.
> > > > >> > > > > >
> > > > >> > > > > >
> > > > >> > > > > > >
> > > > >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> > > > >> gwen@confluent.io
> > > > >> > >
> > > > >> > > > > wrote:
> > > > >> > > > > > >
> > > > >> > > > > > >> Regarding the change to the assignment field. It
> would
> > > be a
> > > > >> > > protocol
> > > > >> > > > > > bump,
> > > > >> > > > > > >> otherwise consumers will not know how to parse the
> > bytes
> > > > the
> > > > >> > > broker
> > > > >> > > > is
> > > > >> > > > > > >> returning, right?
> > > > >> > > > > > >> Or did I misunderstand the suggestion?
> > > > >> > > > > > >>
> > > > >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> > > > >> > > wangguoz@gmail.com>
> > > > >> > > > > > >> wrote:
> > > > >> > > > > > >>
> > > > >> > > > > > >> > I think for just solving issue 1), Jun's suggestion
> > is
> > > > >> > > sufficient
> > > > >> > > > > and
> > > > >> > > > > > >> > simple. So I'd prefer that approach.
> > > > >> > > > > > >> >
> > > > >> > > > > > >> > In addition, Jason's optimization on the assignment
> > > field
> > > > >> > would
> > > > >> > > be
> > > > >> > > > > > good
> > > > >> > > > > > >> for
> > > > >> > > > > > >> > 2) and 3) as well, and I like that optimization for
> > its
> > > > >> > > simplicity
> > > > >> > > > > and
> > > > >> > > > > > >> no
> > > > >> > > > > > >> > format change as well. And in the future I'm in
> favor
> > > of
> > > > >> > > > considering
> > > > >> > > > > > to
> > > > >> > > > > > >> > change the in-memory cache format as Jiangjie
> > > suggested.
> > > > >> > > > > > >> >
> > > > >> > > > > > >> > Guozhang
> > > > >> > > > > > >> >
> > > > >> > > > > > >> >
> > > > >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> > > > >> > > > becket.qin@gmail.com>
> > > > >> > > > > > >> wrote:
> > > > >> > > > > > >> >
> > > > >> > > > > > >> > > Hi Jason,
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > There are a few problems we want to solve here:
> > > > >> > > > > > >> > > 1. The group metadata is too big to be appended
> to
> > > the
> > > > >> log.
> > > > >> > > > > > >> > > 2. Reduce the memory footprint on the broker
> > > > >> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > To solve (1), I like your idea of having separate
> > > > >> messages
> > > > >> > per
> > > > >> > > > > > member.
> > > > >> > > > > > >> > The
> > > > >> > > > > > >> > > proposal (Onur's option 8) is to break metadata
> > into
> > > > >> small
> > > > >> > > > records
> > > > >> > > > > > in
> > > > >> > > > > > >> the
> > > > >> > > > > > >> > > same uncompressed message set so each record is
> > > small.
> > > > I
> > > > >> > agree
> > > > >> > > > it
> > > > >> > > > > > >> would
> > > > >> > > > > > >> > be
> > > > >> > > > > > >> > > ideal if we are able to store the metadata
> > separately
> > > > for
> > > > >> > each
> > > > >> > > > > > >> member. I
> > > > >> > > > > > >> > > was also thinking about storing the metadata into
> > > > >> multiple
> > > > >> > > > > messages,
> > > > >> > > > > > >> too.
> > > > >> > > > > > >> > > What concerns me was that having multiple
> messages
> > > > seems
> > > > >> > > > breaking
> > > > >> > > > > > the
> > > > >> > > > > > >> > > atomicity. I am not sure how we are going to deal
> > > with
> > > > >> the
> > > > >> > > > > potential
> > > > >> > > > > > >> > > issues. For example, What if group metadata is
> > > > replicated
> > > > >> > but
> > > > >> > > > the
> > > > >> > > > > > >> member
> > > > >> > > > > > >> > > metadata is not? It might be fine depending on
> the
> > > > >> > > > implementation
> > > > >> > > > > > >> though,
> > > > >> > > > > > >> > > but I am not sure.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > For (2) we want to store the metadata onto the
> > disk,
> > > > >> which
> > > > >> > is
> > > > >> > > > what
> > > > >> > > > > > we
> > > > >> > > > > > >> > have
> > > > >> > > > > > >> > > to do anyway. The only question is in what format
> > > > should
> > > > >> we
> > > > >> > > > store
> > > > >> > > > > > >> them.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > To address (3) we want to have the metadata to be
> > > > >> > compressed,
> > > > >> > > > > which
> > > > >> > > > > > is
> > > > >> > > > > > >> > > contradict to the the above solution of (1).
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > I think Jun's suggestion is probably still the
> > > > simplest.
> > > > >> To
> > > > >> > > > avoid
> > > > >> > > > > > >> > changing
> > > > >> > > > > > >> > > the behavior for consumers, maybe we can do that
> > only
> > > > for
> > > > >> > > > > > >> offset_topic,
> > > > >> > > > > > >> > > i.e, if the max fetch bytes of the fetch request
> is
> > > > >> smaller
> > > > >> > > than
> > > > >> > > > > the
> > > > >> > > > > > >> > > message size on the offset topic, we always
> return
> > at
> > > > >> least
> > > > >> > > one
> > > > >> > > > > full
> > > > >> > > > > > >> > > message. This should avoid the unexpected problem
> > on
> > > > the
> > > > >> > > client
> > > > >> > > > > side
> > > > >> > > > > > >> > > because supposedly only tools and brokers will
> > fetch
> > > > from
> > > > >> > the
> > > > >> > > > the
> > > > >> > > > > > >> > internal
> > > > >> > > > > > >> > > topics,
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > As a modification to what you suggested, one
> > > solution I
> > > > >> was
> > > > >> > > > > thinking
> > > > >> > > > > > >> was
> > > > >> > > > > > >> > to
> > > > >> > > > > > >> > > have multiple messages in a single compressed
> > > message.
> > > > >> That
> > > > >> > > > means
> > > > >> > > > > > for
> > > > >> > > > > > >> > > SyncGroupResponse we still need to read the
> entire
> > > > >> > compressed
> > > > >> > > > > > messages
> > > > >> > > > > > >> > and
> > > > >> > > > > > >> > > extract the inner messages, which seems not quite
> > > > >> different
> > > > >> > > from
> > > > >> > > > > > >> having a
> > > > >> > > > > > >> > > single message containing everything. But let me
> > just
> > > > >> put it
> > > > >> > > > here
> > > > >> > > > > > and
> > > > >> > > > > > >> see
> > > > >> > > > > > >> > > if that makes sense.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > We can have a map of GroupMetadataKey ->
> > > > >> > > > GroupMetadataValueOffset.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > The GroupMetadataValue is stored in a compressed
> > > > message.
> > > > >> > The
> > > > >> > > > > inner
> > > > >> > > > > > >> > > messages are the following:
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > Inner Message 0: Version GroupId Generation
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we
> can
> > > > >> compress
> > > > >> > > the
> > > > >> > > > > > bytes
> > > > >> > > > > > >> > here)
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> > > > >> > > > > > >> > > ....
> > > > >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > The MemberMetadata format is the following:
> > > > >> > > > > > >> > >   MemberMetadata => Version Generation ClientId
> > Host
> > > > >> > > > Subscription
> > > > >> > > > > > >> > > Assignment
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > So DescribeGroupResponse will just return the
> > entire
> > > > >> > > compressed
> > > > >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will
> return
> > > the
> > > > >> > > > > > corresponding
> > > > >> > > > > > >> > inner
> > > > >> > > > > > >> > > message.
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > Thanks,
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > Jiangjie (Becket) Qin
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson
> <
> > > > >> > > > > > jason@confluent.io>
> > > > >> > > > > > >> > > wrote:
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > > Hey Becket,
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > I like your idea to store only the offset for
> the
> > > > group
> > > > >> > > > metadata
> > > > >> > > > > > in
> > > > >> > > > > > >> > > memory.
> > > > >> > > > > > >> > > > I think it would be safe to keep it in memory
> > for a
> > > > >> short
> > > > >> > > time
> > > > >> > > > > > after
> > > > >> > > > > > >> > the
> > > > >> > > > > > >> > > > rebalance completes, but after that, it's only
> > real
> > > > >> > purpose
> > > > >> > > is
> > > > >> > > > > to
> > > > >> > > > > > >> > answer
> > > > >> > > > > > >> > > > DescribeGroup requests, so your proposal makes
> a
> > > lot
> > > > of
> > > > >> > > sense
> > > > >> > > > to
> > > > >> > > > > > me.
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > As for the specific problem with the size of
> the
> > > > group
> > > > >> > > > metadata
> > > > >> > > > > > >> message
> > > > >> > > > > > >> > > for
> > > > >> > > > > > >> > > > the MM case, if we cannot succeed in reducing
> the
> > > > size
> > > > >> of
> > > > >> > > the
> > > > >> > > > > > >> > > > subscription/assignment (which I think is still
> > > > >> probably
> > > > >> > the
> > > > >> > > > > best
> > > > >> > > > > > >> > > > alternative if it can work), then I think there
> > are
> > > > >> some
> > > > >> > > > options
> > > > >> > > > > > for
> > > > >> > > > > > >> > > > changing the message format (option #8 in
> Onur's
> > > > >> initial
> > > > >> > > > > e-mail).
> > > > >> > > > > > >> > > > Currently, the key used for storing the group
> > > > metadata
> > > > >> is
> > > > >> > > > this:
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > GroupMetadataKey => Version GroupId
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > And the value is something like this (some
> > details
> > > > >> > elided):
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > GroupMetadataValue => Version GroupId
> Generation
> > > > >> > > > > [MemberMetadata]
> > > > >> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
> > > > >> Assignment
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > I don't think we can change the key without a
> lot
> > > of
> > > > >> pain,
> > > > >> > > but
> > > > >> > > > > it
> > > > >> > > > > > >> seems
> > > > >> > > > > > >> > > > like we can change the value format. Maybe we
> can
> > > > take
> > > > >> the
> > > > >> > > > > > >> > > > subscription/assignment payloads out of the
> value
> > > and
> > > > >> > > > introduce
> > > > >> > > > > a
> > > > >> > > > > > >> new
> > > > >> > > > > > >> > > > "MemberMetadata" message for each member in the
> > > > group.
> > > > >> For
> > > > >> > > > > > example:
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > MemberMetadataValue => Version Generation
> > ClientId
> > > > Host
> > > > >> > > > > > Subscription
> > > > >> > > > > > >> > > > Assignment
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > When a new generation is created, we would
> first
> > > > write
> > > > >> the
> > > > >> > > > group
> > > > >> > > > > > >> > metadata
> > > > >> > > > > > >> > > > message which includes the generation and all
> of
> > > the
> > > > >> > > > memberIds,
> > > > >> > > > > > and
> > > > >> > > > > > >> > then
> > > > >> > > > > > >> > > > we'd write the member metadata messages. To
> > answer
> > > > the
> > > > >> > > > > > DescribeGroup
> > > > >> > > > > > >> > > > request, we'd read the group metadata at the
> > cached
> > > > >> offset
> > > > >> > > > and,
> > > > >> > > > > > >> > depending
> > > > >> > > > > > >> > > > on the version, all of the following member
> > > metadata.
> > > > >> This
> > > > >> > > > would
> > > > >> > > > > > be
> > > > >> > > > > > >> > more
> > > > >> > > > > > >> > > > complex to maintain, but it seems doable if it
> > > comes
> > > > to
> > > > >> > it.
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > Thanks,
> > > > >> > > > > > >> > > > Jason
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> > > > >> > > > > becket.qin@gmail.com
> > > > >> > > > > > >
> > > > >> > > > > > >> > > wrote:
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > > It might worth thinking a little further. We
> > have
> > > > >> > > discussed
> > > > >> > > > > this
> > > > >> > > > > > >> > before
> > > > >> > > > > > >> > > > > that we want to avoid holding all the group
> > > > metadata
> > > > >> in
> > > > >> > > > > memory.
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > I am thinking about the following end state:
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > 1. Enable compression on the offset topic.
> > > > >> > > > > > >> > > > > 2. Instead of holding the entire group
> metadata
> > > in
> > > > >> > memory
> > > > >> > > on
> > > > >> > > > > the
> > > > >> > > > > > >> > > brokers,
> > > > >> > > > > > >> > > > > each broker only keeps a [group -> Offset]
> map,
> > > the
> > > > >> > offset
> > > > >> > > > > > points
> > > > >> > > > > > >> to
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > message in the offset topic which holds the
> > > latest
> > > > >> > > metadata
> > > > >> > > > of
> > > > >> > > > > > the
> > > > >> > > > > > >> > > group.
> > > > >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the
> > > offset
> > > > >> topic
> > > > >> > > > > > directly
> > > > >> > > > > > >> > like
> > > > >> > > > > > >> > > a
> > > > >> > > > > > >> > > > > normal consumption, except that only exactly
> > one
> > > > >> message
> > > > >> > > > will
> > > > >> > > > > be
> > > > >> > > > > > >> > > > returned.
> > > > >> > > > > > >> > > > > 4. SyncGroupResponse will read the message,
> > > extract
> > > > >> the
> > > > >> > > > > > assignment
> > > > >> > > > > > >> > part
> > > > >> > > > > > >> > > > and
> > > > >> > > > > > >> > > > > send back the partition assignment. We can
> > > compress
> > > > >> the
> > > > >> > > > > > partition
> > > > >> > > > > > >> > > > > assignment before sends it out if we want.
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > Jiangjie (Becket) Qin
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason
> > Gustafson
> > > <
> > > > >> > > > > > >> jason@confluent.io
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> > > > > wrote:
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > Jason, doesn't gzip (or other
> compression)
> > > > >> basically
> > > > >> > > do
> > > > >> > > > > > this?
> > > > >> > > > > > >> If
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > > topic
> > > > >> > > > > > >> > > > > > > is a string and the topic is repeated
> > > > throughout,
> > > > >> > > won't
> > > > >> > > > > > >> > compression
> > > > >> > > > > > >> > > > > > > basically replace all repeated instances
> of
> > > it
> > > > >> with
> > > > >> > an
> > > > >> > > > > index
> > > > >> > > > > > >> > > > reference
> > > > >> > > > > > >> > > > > to
> > > > >> > > > > > >> > > > > > > the full string?
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > > Hey James, yeah, that's probably true, but
> > keep
> > > > in
> > > > >> > mind
> > > > >> > > > that
> > > > >> > > > > > the
> > > > >> > > > > > >> > > > > > compression happens on the broker side. It
> > > would
> > > > be
> > > > >> > nice
> > > > >> > > > to
> > > > >> > > > > > >> have a
> > > > >> > > > > > >> > > more
> > > > >> > > > > > >> > > > > > compact representation so that get some
> > benefit
> > > > >> over
> > > > >> > the
> > > > >> > > > > wire
> > > > >> > > > > > as
> > > > >> > > > > > >> > > well.
> > > > >> > > > > > >> > > > > This
> > > > >> > > > > > >> > > > > > seems to be less of a concern here, so the
> > > bigger
> > > > >> > gains
> > > > >> > > > are
> > > > >> > > > > > >> > probably
> > > > >> > > > > > >> > > > from
> > > > >> > > > > > >> > > > > > reducing the number of partitions that need
> > to
> > > be
> > > > >> > listed
> > > > >> > > > > > >> > > individually.
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > > -Jason
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur
> > Karaman <
> > > > >> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> > > > >> > > > > > >> > > > > > wrote:
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > > > When figuring out these optimizations,
> it's
> > > > worth
> > > > >> > > > keeping
> > > > >> > > > > in
> > > > >> > > > > > >> mind
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > > > improvements when the message is
> > uncompressed
> > > > vs
> > > > >> > when
> > > > >> > > > it's
> > > > >> > > > > > >> > > > compressed.
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > When uncompressed:
> > > > >> > > > > > >> > > > > > > Fixing the Assignment serialization to
> > > instead
> > > > >> be a
> > > > >> > > > topic
> > > > >> > > > > > >> index
> > > > >> > > > > > >> > > into
> > > > >> > > > > > >> > > > > the
> > > > >> > > > > > >> > > > > > > corresponding member's subscription list
> > > would
> > > > >> > usually
> > > > >> > > > be
> > > > >> > > > > a
> > > > >> > > > > > >> good
> > > > >> > > > > > >> > > > thing.
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > I think the proposal is only worse when
> the
> > > > topic
> > > > >> > > names
> > > > >> > > > > are
> > > > >> > > > > > >> > small.
> > > > >> > > > > > >> > > > The
> > > > >> > > > > > >> > > > > > > Type.STRING we use in our protocol for
> the
> > > > >> > > assignment's
> > > > >> > > > > > >> > > > TOPIC_KEY_NAME
> > > > >> > > > > > >> > > > > is
> > > > >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so
> > our
> > > > >> strings
> > > > >> > > are
> > > > >> > > > > > first
> > > > >> > > > > > >> > > > > prepended
> > > > >> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > The new proposal does worse when:
> > > > >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> > > > >> > index_type_size
> > > > >> > > > > > >> > > > > > > in other words when:
> > > > >> > > > > > >> > > > > > > utf_encoded_string_payload_size <
> > > > >> index_type_size -
> > > > >> > 2
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > If the index type ends up being
> Type.INT32,
> > > > then
> > > > >> the
> > > > >> > > > > > proposal
> > > > >> > > > > > >> is
> > > > >> > > > > > >> > > > worse
> > > > >> > > > > > >> > > > > > when
> > > > >> > > > > > >> > > > > > > the topic is length 1.
> > > > >> > > > > > >> > > > > > > If the index type ends up being
> Type.INT64,
> > > > then
> > > > >> the
> > > > >> > > > > > proposal
> > > > >> > > > > > >> is
> > > > >> > > > > > >> > > > worse
> > > > >> > > > > > >> > > > > > when
> > > > >> > > > > > >> > > > > > > the topic is less than length 6.
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > When compressed:
> > > > >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure
> how
> > > > >> things
> > > > >> > > > change
> > > > >> > > > > > when
> > > > >> > > > > > >> > > > > > compression
> > > > >> > > > > > >> > > > > > > comes into the picture. This would be
> worth
> > > > >> > > > investigating.
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James
> > Cheng
> > > <
> > > > >> > > > > > >> > wushujames@gmail.com
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > > > wrote:
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
> > > > >> Gustafson <
> > > > >> > > > > > >> > > > jason@confluent.io>
> > > > >> > > > > > >> > > > > > > > wrote:
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay
> > out
> > > > the
> > > > >> > > > > assignment
> > > > >> > > > > > >> > without
> > > > >> > > > > > >> > > > > > needing
> > > > >> > > > > > >> > > > > > > > to
> > > > >> > > > > > >> > > > > > > > > explicitly repeat the topic? For
> > example,
> > > > the
> > > > >> > > leader
> > > > >> > > > > > could
> > > > >> > > > > > >> > sort
> > > > >> > > > > > >> > > > the
> > > > >> > > > > > >> > > > > > > > topics
> > > > >> > > > > > >> > > > > > > > > for each member and just use an
> integer
> > > to
> > > > >> > > represent
> > > > >> > > > > the
> > > > >> > > > > > >> > index
> > > > >> > > > > > >> > > of
> > > > >> > > > > > >> > > > > > each
> > > > >> > > > > > >> > > > > > > > > topic within the sorted list (note
> this
> > > > >> depends
> > > > >> > on
> > > > >> > > > the
> > > > >> > > > > > >> > > > subscription
> > > > >> > > > > > >> > > > > > > > > including the full topic list).
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex
> [Partition]]
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other
> > compression)
> > > > >> > basically
> > > > >> > > > do
> > > > >> > > > > > >> this?
> > > > >> > > > > > >> > If
> > > > >> > > > > > >> > > > the
> > > > >> > > > > > >> > > > > > > topic
> > > > >> > > > > > >> > > > > > > > is a string and the topic is repeated
> > > > >> throughout,
> > > > >> > > > won't
> > > > >> > > > > > >> > > compression
> > > > >> > > > > > >> > > > > > > > basically replace all repeated
> instances
> > of
> > > > it
> > > > >> > with
> > > > >> > > an
> > > > >> > > > > > index
> > > > >> > > > > > >> > > > > reference
> > > > >> > > > > > >> > > > > > to
> > > > >> > > > > > >> > > > > > > > the full string?
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > > > -James
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > > > > You could even combine these two
> > options
> > > so
> > > > >> that
> > > > >> > > you
> > > > >> > > > > > have
> > > > >> > > > > > >> > only
> > > > >> > > > > > >> > > 3
> > > > >> > > > > > >> > > > > > > integers
> > > > >> > > > > > >> > > > > > > > > for each topic assignment:
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex
> MinPartition
> > > > >> > > MaxPartition]
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > There may even be better options
> with a
> > > > >> little
> > > > >> > > more
> > > > >> > > > > > >> thought.
> > > > >> > > > > > >> > > All
> > > > >> > > > > > >> > > > of
> > > > >> > > > > > >> > > > > > > this
> > > > >> > > > > > >> > > > > > > > is
> > > > >> > > > > > >> > > > > > > > > just part of the client-side
> protocol,
> > so
> > > > it
> > > > >> > > > wouldn't
> > > > >> > > > > > >> require
> > > > >> > > > > > >> > > any
> > > > >> > > > > > >> > > > > > > version
> > > > >> > > > > > >> > > > > > > > > bumps on the broker. What do you
> think?
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > Thanks,
> > > > >> > > > > > >> > > > > > > > > Jason
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM,
> > Guozhang
> > > > >> Wang <
> > > > >> > > > > > >> > > > wangguoz@gmail.com
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > > > > > wrote:
> > > > >> > > > > > >> > > > > > > > >
> > > > >> > > > > > >> > > > > > > > >> The original concern is that regex
> may
> > > not
> > > > >> be
> > > > >> > > > > > efficiently
> > > > >> > > > > > >> > > > > supported
> > > > >> > > > > > >> > > > > > > > >> across-languages, but if there is a
> > neat
> > > > >> > > > workaround I
> > > > >> > > > > > >> would
> > > > >> > > > > > >> > > love
> > > > >> > > > > > >> > > > > to
> > > > >> > > > > > >> > > > > > > > learn.
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >> Guozhang
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM,
> > Ismael
> > > > >> Juma <
> > > > >> > > > > > >> > > ismael@juma.me.uk
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > > > > > wrote:
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>> Having said that, as a general
> > point, I
> > > > >> think
> > > > >> > we
> > > > >> > > > > > should
> > > > >> > > > > > >> > > > consider
> > > > >> > > > > > >> > > > > > > > >> supporting
> > > > >> > > > > > >> > > > > > > > >>> topic patterns in the wire
> protocol.
> > It
> > > > >> > requires
> > > > >> > > > > some
> > > > >> > > > > > >> > > thinking
> > > > >> > > > > > >> > > > > for
> > > > >> > > > > > >> > > > > > > > >>> cross-language support, but it
> seems
> > > > >> > > surmountable
> > > > >> > > > > and
> > > > >> > > > > > it
> > > > >> > > > > > >> > > could
> > > > >> > > > > > >> > > > > make
> > > > >> > > > > > >> > > > > > > > >> certain
> > > > >> > > > > > >> > > > > > > > >>> operations a lot more efficient
> (the
> > > fact
> > > > >> > that a
> > > > >> > > > > basic
> > > > >> > > > > > >> > regex
> > > > >> > > > > > >> > > > > > > > subscription
> > > > >> > > > > > >> > > > > > > > >>> causes the consumer to request
> > metadata
> > > > for
> > > > >> > all
> > > > >> > > > > topics
> > > > >> > > > > > >> is
> > > > >> > > > > > >> > not
> > > > >> > > > > > >> > > > > > great).
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>> Ismael
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM,
> > > > Guozhang
> > > > >> > Wang
> > > > >> > > <
> > > > >> > > > > > >> > > > > > wangguoz@gmail.com>
> > > > >> > > > > > >> > > > > > > > >>> wrote:
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in
> changing
> > > the
> > > > >> > > handling
> > > > >> > > > > > >> logics of
> > > > >> > > > > > >> > > > > single
> > > > >> > > > > > >> > > > > > > > large
> > > > >> > > > > > >> > > > > > > > >>>> message on the consumer side.
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>> As for the case of "a single group
> > > > >> > subscribing
> > > > >> > > to
> > > > >> > > > > > 3000
> > > > >> > > > > > >> > > > topics",
> > > > >> > > > > > >> > > > > > with
> > > > >> > > > > > >> > > > > > > > >> 100
> > > > >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
> > > > >> reasonable
> > > > >> > to
> > > > >> > > me
> > > > >> > > > > > (when
> > > > >> > > > > > >> > > > storing
> > > > >> > > > > > >> > > > > in
> > > > >> > > > > > >> > > > > > > ZK,
> > > > >> > > > > > >> > > > > > > > >> we
> > > > >> > > > > > >> > > > > > > > >>>> also have the znode limit which is
> > set
> > > > to
> > > > >> 1Mb
> > > > >> > > by
> > > > >> > > > > > >> default,
> > > > >> > > > > > >> > > > though
> > > > >> > > > > > >> > > > > > > > >>> admittedly
> > > > >> > > > > > >> > > > > > > > >>>> it is only for one consumer). And
> if
> > > we
> > > > do
> > > > >> > the
> > > > >> > > > > change
> > > > >> > > > > > >> as
> > > > >> > > > > > >> > Jun
> > > > >> > > > > > >> > > > > > > > suggested,
> > > > >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory
> pressure
> > is
> > > > OK
> > > > >> I
> > > > >> > > > think.
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>> Guozhang
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM,
> > Onur
> > > > >> > Karaman
> > > > >> > > <
> > > > >> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> > > > >> > > > > > >> > > > > > > > >>>>> wrote:
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>>> Results without compression:
> > > > >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the
> > > tipping
> > > > >> > point
> > > > >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> > > > >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>
> > > > >> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression
> > > > shrinks
> > > > >> > the
> > > > >> > > > > > message
> > > > >> > > > > > >> > size
> > > > >> > > > > > >> > > by
> > > > >> > > > > > >> > > > > 4x.
> > > > >> > > > > > >> > > > > > > > >>>>>
> > > > >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM,
> > Jun
> > > > Rao
> > > > >> <
> > > > >> > > > > > >> > jun@confluent.io
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > > > > > wrote:
> > > > >> > > > > > >> > > > > > > > >>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>> Onur,
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix
> how
> > we
> > > > >> deal
> > > > >> > > with
> > > > >> > > > > the
> > > > >> > > > > > >> case
> > > > >> > > > > > >> > > > when a
> > > > >> > > > > > >> > > > > > > > >>> message
> > > > >> > > > > > >> > > > > > > > >>>> is
> > > > >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size.
> Today,
> > > if
> > > > >> the
> > > > >> > > fetch
> > > > >> > > > > > size
> > > > >> > > > > > >> is
> > > > >> > > > > > >> > > > > smaller
> > > > >> > > > > > >> > > > > > > > >> than
> > > > >> > > > > > >> > > > > > > > >>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will
> get
> > > > stuck.
> > > > >> > > > Instead,
> > > > >> > > > > > we
> > > > >> > > > > > >> can
> > > > >> > > > > > >> > > > > simply
> > > > >> > > > > > >> > > > > > > > >>> return
> > > > >> > > > > > >> > > > > > > > >>>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>> full message if it's larger than
> > the
> > > > >> fetch
> > > > >> > > size
> > > > >> > > > > w/o
> > > > >> > > > > > >> > > > requiring
> > > > >> > > > > > >> > > > > > the
> > > > >> > > > > > >> > > > > > > > >>>>> consumer
> > > > >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch
> size.
> > > On
> > > > >> the
> > > > >> > > > broker
> > > > >> > > > > > >> side,
> > > > >> > > > > > >> > to
> > > > >> > > > > > >> > > > > serve
> > > > >> > > > > > >> > > > > > a
> > > > >> > > > > > >> > > > > > > > >>> fetch
> > > > >> > > > > > >> > > > > > > > >>>>>> request, we already do an index
> > > lookup
> > > > >> and
> > > > >> > > then
> > > > >> > > > > > scan
> > > > >> > > > > > >> the
> > > > >> > > > > > >> > > > log a
> > > > >> > > > > > >> > > > > > bit
> > > > >> > > > > > >> > > > > > > > >> to
> > > > >> > > > > > >> > > > > > > > >>>>> find
> > > > >> > > > > > >> > > > > > > > >>>>>> the message with the requested
> > > offset.
> > > > >> We
> > > > >> > can
> > > > >> > > > > just
> > > > >> > > > > > >> check
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > > size
> > > > >> > > > > > >> > > > > > > > >> of
> > > > >> > > > > > >> > > > > > > > >>>> that
> > > > >> > > > > > >> > > > > > > > >>>>>> message and return the full
> > message
> > > if
> > > > >> its
> > > > >> > > size
> > > > >> > > > > is
> > > > >> > > > > > >> > larger
> > > > >> > > > > > >> > > > than
> > > > >> > > > > > >> > > > > > the
> > > > >> > > > > > >> > > > > > > > >>>> fetch
> > > > >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is
> > really
> > > > for
> > > > >> > > > > > performance
> > > > >> > > > > > >> > > > > > optimization,
> > > > >> > > > > > >> > > > > > > > >>> i.e.
> > > > >> > > > > > >> > > > > > > > >>>>> in
> > > > >> > > > > > >> > > > > > > > >>>>>> the common case, we will not
> > return
> > > > more
> > > > >> > > bytes
> > > > >> > > > > than
> > > > >> > > > > > >> > fetch
> > > > >> > > > > > >> > > > > size,
> > > > >> > > > > > >> > > > > > > but
> > > > >> > > > > > >> > > > > > > > >>> if
> > > > >> > > > > > >> > > > > > > > >>>>>> there is a large message, we
> will
> > > > return
> > > > >> > more
> > > > >> > > > > bytes
> > > > >> > > > > > >> than
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > > > > >>> specified
> > > > >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large
> > > > messages
> > > > >> are
> > > > >> > > > rare.
> > > > >> > > > > > >> So, it
> > > > >> > > > > > >> > > > > > shouldn't
> > > > >> > > > > > >> > > > > > > > >>>>> increase
> > > > >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the
> > client
> > > > too
> > > > >> > > much.
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>> Jun
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM,
> > > Onur
> > > > >> > > Karaman <
> > > > >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> > > > >> > > > > > >> > > > > > > > >>>>>> wrote:
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started
> doing
> > > some
> > > > >> > tests
> > > > >> > > on
> > > > >> > > > > the
> > > > >> > > > > > >> new
> > > > >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> > > > >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more
> > > > >> strenuous
> > > > >> > use
> > > > >> > > > > cases
> > > > >> > > > > > >> like
> > > > >> > > > > > >> > > > > > mirroring
> > > > >> > > > > > >> > > > > > > > >>>>>> clusters
> > > > >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and
> > > thought
> > > > >> I'd
> > > > >> > > share
> > > > >> > > > > > >> > whatever I
> > > > >> > > > > > >> > > > > have
> > > > >> > > > > > >> > > > > > so
> > > > >> > > > > > >> > > > > > > > >>>> far.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the
> amount
> > > of
> > > > >> group
> > > > >> > > > > > metadata
> > > > >> > > > > > >> we
> > > > >> > > > > > >> > > can
> > > > >> > > > > > >> > > > > fit
> > > > >> > > > > > >> > > > > > > > >> into
> > > > >> > > > > > >> > > > > > > > >>>> one
> > > > >> > > > > > >> > > > > > > > >>>>>>> message
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Some background:
> > > > >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is
> > > implemented
> > > > >> in
> > > > >> > two
> > > > >> > > > > > phases
> > > > >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase
> > that
> > > > >> > > identifies
> > > > >> > > > > > >> members
> > > > >> > > > > > >> > of
> > > > >> > > > > > >> > > > the
> > > > >> > > > > > >> > > > > > > > >> group
> > > > >> > > > > > >> > > > > > > > >>>> and
> > > > >> > > > > > >> > > > > > > > >>>>>>> aggregates member
> subscriptions.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that
> > waits
> > > > for
> > > > >> > the
> > > > >> > > > > group
> > > > >> > > > > > >> > leader
> > > > >> > > > > > >> > > to
> > > > >> > > > > > >> > > > > > > > >> decide
> > > > >> > > > > > >> > > > > > > > >>>>> member
> > > > >> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
> > > > >> > > subscriptions
> > > > >> > > > > > across
> > > > >> > > > > > >> > the
> > > > >> > > > > > >> > > > > group.
> > > > >> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this
> > > decision
> > > > >> > with a
> > > > >> > > > > > >> > > > > SyncGroupRequest.
> > > > >> > > > > > >> > > > > > > > >> The
> > > > >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> > > > >> SyncGroupRequests
> > > > >> > > by
> > > > >> > > > > > >> appending
> > > > >> > > > > > >> > > all
> > > > >> > > > > > >> > > > > > group
> > > > >> > > > > > >> > > > > > > > >>>> state
> > > > >> > > > > > >> > > > > > > > >>>>>>> into a single message under the
> > > > >> > > > > __consumer_offsets
> > > > >> > > > > > >> > topic.
> > > > >> > > > > > >> > > > > This
> > > > >> > > > > > >> > > > > > > > >>>> message
> > > > >> > > > > > >> > > > > > > > >>>>> is
> > > > >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and
> > contains
> > > > each
> > > > >> > > member
> > > > >> > > > > > >> > > subscription
> > > > >> > > > > > >> > > > > as
> > > > >> > > > > > >> > > > > > > > >> well
> > > > >> > > > > > >> > > > > > > > >>>> as
> > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each
> > member.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> The environment:
> > > > >> > > > > > >> > > > > > > > >>>>>>> - one broker
> > > > >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets
> > partition
> > > > >> > > > > > >> > > > > > > > >>>>>>> -
> > offsets.topic.compression.codec=1
> > > > //
> > > > >> > this
> > > > >> > > is
> > > > >> > > > > > gzip
> > > > >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending
> > KAFKA-3718
> > > > >> patch
> > > > >> > > that
> > > > >> > > > > > >> actually
> > > > >> > > > > > >> > > > makes
> > > > >> > > > > > >> > > > > > use
> > > > >> > > > > > >> > > > > > > > >> of
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> offsets.topic.compression.codec:
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> https://github.com/apache/kafka/pull/1394
> > > > >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is
> an
> > > > actual
> > > > >> > > subset
> > > > >> > > > > of
> > > > >> > > > > > >> > topics
> > > > >> > > > > > >> > > > from
> > > > >> > > > > > >> > > > > > one
> > > > >> > > > > > >> > > > > > > > >>> of
> > > > >> > > > > > >> > > > > > > > >>>>> our
> > > > >> > > > > > >> > > > > > > > >>>>>>> clusters.
> > > > >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> > > > >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long
> > on
> > > > >> average
> > > > >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying
> number
> > > of
> > > > >> > > consumers
> > > > >> > > > > > each
> > > > >> > > > > > >> > > > hardcoded
> > > > >> > > > > > >> > > > > > > > >> with
> > > > >> > > > > > >> > > > > > > > >>>> all
> > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests
> > more
> > > > >> > > consistent.
> > > > >> > > > > > >> > > wildcarding
> > > > >> > > > > > >> > > > > with
> > > > >> > > > > > >> > > > > > > > >> .*
> > > > >> > > > > > >> > > > > > > > >>>>> should
> > > > >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> > > > >> subscription
> > > > >> > > > hits
> > > > >> > > > > > the
> > > > >> > > > > > >> > > > > coordinator
> > > > >> > > > > > >> > > > > > > > >> as
> > > > >> > > > > > >> > > > > > > > >>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>>> subscription has already been
> > fully
> > > > >> > expanded
> > > > >> > > > out
> > > > >> > > > > > to
> > > > >> > > > > > >> the
> > > > >> > > > > > >> > > > list
> > > > >> > > > > > >> > > > > of
> > > > >> > > > > > >> > > > > > > > >>>> topics
> > > > >> > > > > > >> > > > > > > > >>>>> by
> > > > >> > > > > > >> > > > > > > > >>>>>>> the consumers.
> > > > >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to
> > > > >> Log.scala
> > > > >> > to
> > > > >> > > > > print
> > > > >> > > > > > >> out
> > > > >> > > > > > >> > the
> > > > >> > > > > > >> > > > > > message
> > > > >> > > > > > >> > > > > > > > >>>> sizes
> > > > >> > > > > > >> > > > > > > > >>>>>>> after compression
> > > > >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all
> > and
> > > > >> auto
> > > > >> > > > commits
> > > > >> > > > > > are
> > > > >> > > > > > >> > > > > disabled.
> > > > >> > > > > > >> > > > > > > > >> The
> > > > >> > > > > > >> > > > > > > > >>>> only
> > > > >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting
> added
> > > is
> > > > >> the
> > > > >> > > > > > >> > > __consumer_offsets
> > > > >> > > > > > >> > > > > > topic
> > > > >> > > > > > >> > > > > > > > >>> and
> > > > >> > > > > > >> > > > > > > > >>>>>>> they're only from storing group
> > > > >> metadata
> > > > >> > > while
> > > > >> > > > > > >> > processing
> > > > >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Results:
> > > > >> > > > > > >> > > > > > > > >>>>>>> The results below show that we
> > > exceed
> > > > >> the
> > > > >> > > > > 1000012
> > > > >> > > > > > >> byte
> > > > >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes
> limit
> > > > >> > relatively
> > > > >> > > > > > quickly
> > > > >> > > > > > >> > > > (between
> > > > >> > > > > > >> > > > > > > > >> 30-40
> > > > >> > > > > > >> > > > > > > > >>>>>>> consumers):
> > > > >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes *
> the
> > > > >> tipping
> > > > >> > > point
> > > > >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is
> > > pretty
> > > > >> > > gradual.
> > > > >> > > > > > >> Plotting
> > > > >> > > > > > >> > > the
> > > > >> > > > > > >> > > > > > > > >> points
> > > > >> > > > > > >> > > > > > > > >>>>> makes
> > > > >> > > > > > >> > > > > > > > >>>>>> it
> > > > >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the
> > > number
> > > > of
> > > > >> > > > > consumers:
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> >
> > > > >> > > > > > >>
> > > > >> > > > > >
> > > > >> > > > >
> > > > >> > > >
> > > > >> > >
> > > > >> >
> > > > >>
> > > >
> > >
> >
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers
> > aren't
> > > > >> > averages
> > > > >> > > > or
> > > > >> > > > > > >> medians
> > > > >> > > > > > >> > > or
> > > > >> > > > > > >> > > > > > > > >> anything
> > > > >> > > > > > >> > > > > > > > >>>>> like
> > > > >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size
> > from
> > > a
> > > > >> given
> > > > >> > > > run.
> > > > >> > > > > I
> > > > >> > > > > > >> did
> > > > >> > > > > > >> > run
> > > > >> > > > > > >> > > > > them
> > > > >> > > > > > >> > > > > > a
> > > > >> > > > > > >> > > > > > > > >>> few
> > > > >> > > > > > >> > > > > > > > >>>>>> times
> > > > >> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Impact:
> > > > >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> > > > >> > > > __consumer_offsets
> > > > >> > > > > > >> topic
> > > > >> > > > > > >> > > with
> > > > >> > > > > > >> > > > > my
> > > > >> > > > > > >> > > > > > > > >>>> pending
> > > > >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the
> > AwaitingSync
> > > > >> phase
> > > > >> > of
> > > > >> > > > the
> > > > >> > > > > > >> group
> > > > >> > > > > > >> > > fails
> > > > >> > > > > > >> > > > > > with
> > > > >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This
> > means
> > > > the
> > > > >> > > > combined
> > > > >> > > > > > >> size
> > > > >> > > > > > >> > of
> > > > >> > > > > > >> > > > each
> > > > >> > > > > > >> > > > > > > > >>>> member's
> > > > >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments
> > > > exceeded
> > > > >> the
> > > > >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> > > > >> > > > > > >> > > > > > > > >>>>> of
> > > > >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends
> up
> > > > dying.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Options:
> > > > >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the
> > number
> > > > of
> > > > >> > > > consumers
> > > > >> > > > > > in
> > > > >> > > > > > >> the
> > > > >> > > > > > >> > > > > group.
> > > > >> > > > > > >> > > > > > > > >> This
> > > > >> > > > > > >> > > > > > > > >>>>> isn't
> > > > >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in
> more
> > > > >> > strenuous
> > > > >> > > > use
> > > > >> > > > > > >> cases
> > > > >> > > > > > >> > > like
> > > > >> > > > > > >> > > > > > > > >>>> MirrorMaker
> > > > >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the
> group
> > > > into
> > > > >> > > smaller
> > > > >> > > > > > >> groups
> > > > >> > > > > > >> > > which
> > > > >> > > > > > >> > > > > > > > >>> together
> > > > >> > > > > > >> > > > > > > > >>>>> will
> > > > >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the
> topics.
> > > This
> > > > >> > gives
> > > > >> > > > each
> > > > >> > > > > > >> group
> > > > >> > > > > > >> > > > > member a
> > > > >> > > > > > >> > > > > > > > >>>> smaller
> > > > >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics
> > > > >> starting
> > > > >> > > with
> > > > >> > > > > a-m
> > > > >> > > > > > >> while
> > > > >> > > > > > >> > > g2
> > > > >> > > > > > >> > > > > has
> > > > >> > > > > > >> > > > > > > > >>> topics
> > > > >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would
> be
> > > > >> > > operationally
> > > > >> > > > > > >> painful
> > > > >> > > > > > >> > to
> > > > >> > > > > > >> > > > > > manage.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the
> > topics
> > > > >> among
> > > > >> > > > members
> > > > >> > > > > > of
> > > > >> > > > > > >> the
> > > > >> > > > > > >> > > > > group.
> > > > >> > > > > > >> > > > > > > > >>> Again
> > > > >> > > > > > >> > > > > > > > >>>>> this
> > > > >> > > > > > >> > > > > > > > >>>>>>> gives each group member a
> smaller
> > > > >> > > > subscription.
> > > > >> > > > > > This
> > > > >> > > > > > >> > > would
> > > > >> > > > > > >> > > > > also
> > > > >> > > > > > >> > > > > > > > >> be
> > > > >> > > > > > >> > > > > > > > >>>>>>> operationally painful to
> manage.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> > > > >> > > > > > >> KafkaConfig.messageMaxBytes
> > > > >> > > > > > >> > (a
> > > > >> > > > > > >> > > > > > > > >>> topic-level
> > > > >> > > > > > >> > > > > > > > >>>>>>> config) and
> > > > >> > KafkaConfig.replicaFetchMaxBytes
> > > > >> > > > (a
> > > > >> > > > > > >> > > > broker-level
> > > > >> > > > > > >> > > > > > > > >>> config).
> > > > >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to
> just
> > > the
> > > > >> > > > > > >> __consumer_offsets
> > > > >> > > > > > >> > > > topic
> > > > >> > > > > > >> > > > > > > > >> seems
> > > > >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but
> bumping
> > up
> > > > the
> > > > >> > > > > > broker-level
> > > > >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> > > > >> > > > > > >> > > > > > > > >>>>>>> would probably need more
> > attention.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
> > > > >> > compression
> > > > >> > > > > > codecs.
> > > > >> > > > > > >> > Based
> > > > >> > > > > > >> > > > on
> > > > >> > > > > > >> > > > > 2
> > > > >> > > > > > >> > > > > > > > >>>> minutes
> > > > >> > > > > > >> > > > > > > > >>>>> of
> > > > >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and
> > > > snappy
> > > > >> are
> > > > >> > > > > faster
> > > > >> > > > > > >> than
> > > > >> > > > > > >> > > gzip
> > > > >> > > > > > >> > > > > but
> > > > >> > > > > > >> > > > > > > > >>> have
> > > > >> > > > > > >> > > > > > > > >>>>>> worse
> > > > >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably
> > won't
> > > > >> help.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change:
> support
> > > > >> sending
> > > > >> > > the
> > > > >> > > > > > regex
> > > > >> > > > > > >> > over
> > > > >> > > > > > >> > > > the
> > > > >> > > > > > >> > > > > > wire
> > > > >> > > > > > >> > > > > > > > >>>>> instead
> > > > >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> > > > >> > subscriptions. I
> > > > >> > > > > think
> > > > >> > > > > > >> > people
> > > > >> > > > > > >> > > > > said
> > > > >> > > > > > >> > > > > > in
> > > > >> > > > > > >> > > > > > > > >>> the
> > > > >> > > > > > >> > > > > > > > >>>>>> past
> > > > >> > > > > > >> > > > > > > > >>>>>>> that different languages have
> > > subtle
> > > > >> > > > differences
> > > > >> > > > > > in
> > > > >> > > > > > >> > > regex,
> > > > >> > > > > > >> > > > so
> > > > >> > > > > > >> > > > > > > > >> this
> > > > >> > > > > > >> > > > > > > > >>>>>> doesn't
> > > > >> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language
> > > > groups.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe
> > we
> > > > can
> > > > >> > > reverse
> > > > >> > > > > the
> > > > >> > > > > > >> > > mapping?
> > > > >> > > > > > >> > > > > > > > >> Instead
> > > > >> > > > > > >> > > > > > > > >>>> of
> > > > >> > > > > > >> > > > > > > > >>>>>>> mapping from member to
> > > subscriptions,
> > > > >> we
> > > > >> > can
> > > > >> > > > > map a
> > > > >> > > > > > >> > > > > subscription
> > > > >> > > > > > >> > > > > > > > >> to
> > > > >> > > > > > >> > > > > > > > >>> a
> > > > >> > > > > > >> > > > > > > > >>>>> list
> > > > >> > > > > > >> > > > > > > > >>>>>>> of members.
> > > > >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe
> > we
> > > > can
> > > > >> try
> > > > >> > > to
> > > > >> > > > > > break
> > > > >> > > > > > >> > apart
> > > > >> > > > > > >> > > > the
> > > > >> > > > > > >> > > > > > > > >>>>>> subscription
> > > > >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> > > > >> > > SyncGroupRequest
> > > > >> > > > > > into
> > > > >> > > > > > >> > > > multiple
> > > > >> > > > > > >> > > > > > > > >>> records?
> > > > >> > > > > > >> > > > > > > > >>>>>> They
> > > > >> > > > > > >> > > > > > > > >>>>>>> can still go to the same
> message
> > > set
> > > > >> and
> > > > >> > get
> > > > >> > > > > > >> appended
> > > > >> > > > > > >> > > > > together.
> > > > >> > > > > > >> > > > > > > > >>> This
> > > > >> > > > > > >> > > > > > > > >>>>> way
> > > > >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment
> > size,
> > > > >> which
> > > > >> > > > > shouldn't
> > > > >> > > > > > >> be a
> > > > >> > > > > > >> > > > > > problem.
> > > > >> > > > > > >> > > > > > > > >>> This
> > > > >> > > > > > >> > > > > > > > >>>>> can
> > > > >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because
> > > we're
> > > > >> > > currently
> > > > >> > > > > > >> keying
> > > > >> > > > > > >> > > these
> > > > >> > > > > > >> > > > > > > > >>> messages
> > > > >> > > > > > >> > > > > > > > >>>> on
> > > > >> > > > > > >> > > > > > > > >>>>>> the
> > > > >> > > > > > >> > > > > > > > >>>>>>> group, so I think records from
> > the
> > > > same
> > > > >> > > > > rebalance
> > > > >> > > > > > >> might
> > > > >> > > > > > >> > > > > > > > >>> accidentally
> > > > >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> > > > >> understanding
> > > > >> > of
> > > > >> > > > > > >> compaction
> > > > >> > > > > > >> > > > isn't
> > > > >> > > > > > >> > > > > > > > >> that
> > > > >> > > > > > >> > > > > > > > >>>>> great.
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> Todo:
> > > > >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to
> rerun
> > > the
> > > > >> tests
> > > > >> > > > with
> > > > >> > > > > no
> > > > >> > > > > > >> > > > > compression
> > > > >> > > > > > >> > > > > > > > >> just
> > > > >> > > > > > >> > > > > > > > >>>> to
> > > > >> > > > > > >> > > > > > > > >>>>>> see
> > > > >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but
> it's
> > > > >> getting
> > > > >> > > > late.
> > > > >> > > > > > >> Maybe
> > > > >> > > > > > >> > > > > tomorrow?
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>> - Onur
> > > > >> > > > > > >> > > > > > > > >>>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>>
> > > > >> > > > > > >> > > > > > > > >>>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>> --
> > > > >> > > > > > >> > > > > > > > >>>> -- Guozhang
> > > > >> > > > > > >> > > > > > > > >>>>
> > > > >> > > > > > >> > > > > > > > >>>
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > > >> --
> > > > >> > > > > > >> > > > > > > > >> -- Guozhang
> > > > >> > > > > > >> > > > > > > > >>
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > > >
> > > > >> > > > > > >> > > > > > >
> > > > >> > > > > > >> > > > > >
> > > > >> > > > > > >> > > > >
> > > > >> > > > > > >> > > >
> > > > >> > > > > > >> > >
> > > > >> > > > > > >> >
> > > > >> > > > > > >> >
> > > > >> > > > > > >> >
> > > > >> > > > > > >> > --
> > > > >> > > > > > >> > -- Guozhang
> > > > >> > > > > > >> >
> > > > >> > > > > > >>
> > > > >> > > > > > >
> > > > >> > > > > > >
> > > > >> > > > > >
> > > > >> > > > >
> > > > >> > > >
> > > > >> > >
> > > > >> >
> > > > >>
> > > > >
> > > > >
> > > >
> > >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Jason Gustafson <ja...@confluent.io>]

Hi Onur,

I didn't have a specific proposal in mind, I was just thinking analogously
with how Connect ensures task configurations are propagated to tasks
consistently when it rebalances the cluster. The high level concept is to
take the assignment data out of the rebalance protocol itself and replace
it with a pointer. For example, the pointer can be a (topic, partition,
offset) tuple which can be fetched separately by the consumer instance
after the rebalance completes. Then the leader would generate the
assignments, write them to Kafka, and send the pointers to the rest of the
group in the SyncGroup. This is more or less how Connect works.

-Jason

On Thu, Jun 9, 2016 at 11:10 AM, Onur Karaman <okaraman@linkedin.com.invalid
> wrote:

> I think the value of adding a "offsets.replica.fetch.max.bytes" config is
> that we don't break/change the meaning of "replica.fetch.max.bytes".
>
> We can also set "offsets.replica.fetch.max.bytes" to be a value safely
> larger than what we expect to ever allow the __consumer_offsets topic max
> message size to be without doing the larger change of bumping up the global
> "replica.fetch.max.bytes".
>
> On Thu, Jun 9, 2016 at 10:40 AM, Becket Qin <be...@gmail.com> wrote:
>
> > I think taking bigger one of the fetch size and message size limit is
> > probably good enough. If we have a separate
> > "offset.replica.fetch.max.bytes", I guess the value will always be set to
> > max message size of the __consumer_offsets topic, which does not seem to
> > have much value.
> >
> > On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman
> <okaraman@linkedin.com.invalid
> > >
> > wrote:
> >
> > > Maybe another approach can be to add a new
> > > "offsets.replica.fetch.max.bytes" config on the brokers.
> > >
> > > On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <ok...@linkedin.com>
> > > wrote:
> > >
> > > > I made a PR with a tweak to Jun's/Becket's proposal:
> > > > https://github.com/apache/kafka/pull/1484
> > > >
> > > > It just tweaks the fetch behavior specifically for replicas fetching
> > from
> > > > the __consumer_offsets topic when the fetcher's
> > "replica.fetch.max.bytes"
> > > > is less than the __consumer_offset leader's "message.max.bytes" to
> take
> > > the
> > > > max of the two.
> > > >
> > > > I'm honestly not that happy with this solution, as I'd rather not
> > change
> > > > the "replica.fetch.max.bytes" config from being a limit to a
> > > > recommendation. I'd definitely be happy to hear other alternatives!
> > > >
> > > > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> > > > onurkaraman.apache@gmail.com> wrote:
> > > >
> > > >> Sorry I know next to nothing about Kafka Connect. I didn't
> understand
> > > the
> > > >> Kafka Connect / MM idea you brought up. Can you go into more detail?
> > > >>
> > > >> Otherwise I think our remaining options are:
> > > >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
> > > >> __consumer_offsets topic and change the fetch behavior when message
> > size
> > > >> is
> > > >> larger than fetch size
> > > >> - option 6: support sending the regex over the wire instead of the
> > fully
> > > >> expanded topic subscriptions. This should cut down the message size
> > from
> > > >> the subscription side. Again this only helps when pattern-based
> > > >> subscriptions are done.
> > > >>
> > > >> minor correction to an earlier comment I made regarding the message
> > > size:
> > > >> message size ~ sum(s_i + a_i for i in range [1, |C|])
> > > >>
> > > >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <
> jason@confluent.io>
> > > >> wrote:
> > > >>
> > > >> > Hey Onur,
> > > >> >
> > > >> > Thanks for the investigation. It seems the conclusion is that the
> > > >> compact
> > > >> > format helps, but perhaps not enough to justify adding a new
> > > assignment
> > > >> > schema? I'm not sure there's much more room for savings unless we
> > > change
> > > >> > something more fundamental in the assignment approach. We spent
> some
> > > >> time
> > > >> > thinking before about whether we could let the consumers compute
> > their
> > > >> > assignment locally from a smaller set of information, but the
> > > difficulty
> > > >> > (I'm sure you remember) is reaching consensus on topic metadata.
> > Kafka
> > > >> > Connect has a similar problem where all the workers need to agree
> on
> > > >> > connector configurations. Since all configs are stored in a single
> > > topic
> > > >> > partition, the approach we take there is to propagate the offset
> in
> > > the
> > > >> > assignment protocol. Not sure if we could do something similar for
> > > MM...
> > > >> > Anyway, it seems like the best workaround at the moment is Jun's
> > > initial
> > > >> > suggestion. What do you think?
> > > >> >
> > > >> > -Jason
> > > >> >
> > > >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> > > >> > onurkaraman.apache@gmail.com
> > > >> > > wrote:
> > > >> >
> > > >> > > I gave the topic index assignment trick a try against the same
> > > >> > environment.
> > > >> > > The implementation just changed the assignment serialization and
> > > >> > > deserialization logic. It didn't change SyncGroupResponse,
> meaning
> > > it
> > > >> > > continues to exclude the subscription from the SyncGroupResponse
> > and
> > > >> > > assumes the member has kept track of its last subscription.
> > > >> > >
> > > >> > > Assignment topic indexing with compression:
> > > >> > > 1 consumer 34346 bytes
> > > >> > > 5 consumers 177687 bytes
> > > >> > > 10 consumers 331897 bytes
> > > >> > > 20 consumers 572467 bytes
> > > >> > > 30 consumers 811269 bytes
> > > >> > > 40 consumers 1047188 bytes * the tipping point
> > > >> > > 50 consumers 1290092 bytes
> > > >> > > 60 consumers 1527806 bytes
> > > >> > > 70 consumers 1769259 bytes
> > > >> > > 80 consumers 2000118 bytes
> > > >> > > 90 consumers 2244392 bytes
> > > >> > > 100 consumers 2482415 bytes
> > > >> > >
> > > >> > > Assignment topic indexing without compression:
> > > >> > > 1 consumer 211904 bytes
> > > >> > > 5 consumers 677184 bytes
> > > >> > > 10 consumers 1211154 bytes * the tipping point
> > > >> > > 20 consumers 2136196 bytes
> > > >> > > 30 consumers 3061238 bytes
> > > >> > > 40 consumers 3986280 bytes
> > > >> > > 50 consumers 4911322 bytes
> > > >> > > 60 consumers 5836284 bytes
> > > >> > > 70 consumers 6761246 bytes
> > > >> > > 80 consumers 7686208 bytes
> > > >> > > 90 consumers 8611170 bytes
> > > >> > > 100 consumers 9536132 bytes
> > > >> > >
> > > >> > > Assignment topic indexing seems to reduce the size by 500KB
> > without
> > > >> > > compression and 80KB with compression. So assignment topic
> > indexing
> > > >> makes
> > > >> > > some difference in both with and without compression but in our
> > case
> > > >> was
> > > >> > > not nearly enough.
> > > >> > >
> > > >> > > This can be explained by the fact that we aren't actually
> hitting
> > > the
> > > >> > worst
> > > >> > > case scenario of each consumer being assigned a partition from
> > every
> > > >> > topic.
> > > >> > > The reason is simple: a topic can only fully span all the
> > consumers
> > > >> if it
> > > >> > > has at least as many partitions as there are consumers. Given
> that
> > > >> there
> > > >> > > are 8 partitions per topic and we have 100 consumers, it makes
> > sense
> > > >> that
> > > >> > > we aren't close to this worse case scenario where topic indexing
> > > would
> > > >> > make
> > > >> > > a bigger difference.
> > > >> > >
> > > >> > > I tweaked the group leader's assignment code to print out the
> > > >> assignments
> > > >> > > and found that each consumer was getting either 238 or 239
> > > partitions.
> > > >> > Each
> > > >> > > of these partitions were from unique topics. So the consumers
> were
> > > >> really
> > > >> > > getting partitions from 239 topics instead of the full worst
> case
> > > >> > scenario
> > > >> > > of 3000 topics.
> > > >> > >
> > > >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <
> > > jason@confluent.io>
> > > >> > > wrote:
> > > >> > >
> > > >> > > > Gwen, Joel:
> > > >> > > >
> > > >> > > > That's correct. The protocol does allow us to give an assignor
> > its
> > > >> own
> > > >> > > > assignment schema, but I think this will require a couple
> > internal
> > > >> > > changes
> > > >> > > > to the consumer to make use of the full generality.
> > > >> > > >
> > > >> > > > One thing I'm a little uncertain about is whether we should
> use
> > a
> > > >> > > different
> > > >> > > > protocol type. For a little context, the group membership
> > protocol
> > > >> > allows
> > > >> > > > the client to provide a "protocol type" when joining the group
> > to
> > > >> > ensure
> > > >> > > > that all members have some basic semantic compatibility. For
> > > >> example,
> > > >> > the
> > > >> > > > consumer uses "consumer" and Kafka Connect uses "connect."
> > > Currently
> > > >> > all
> > > >> > > > assignors using the "consumer" protocol share a common schema
> > for
> > > >> > > > representing subscriptions and assignment. This is convenient
> > for
> > > >> tools
> > > >> > > > (like consumer-groups.sh) since they just need to know how to
> > > parse
> > > >> the
> > > >> > > > "consumer" protocol type without knowing anything about the
> > > >> assignors.
> > > >> > So
> > > >> > > > introducing another schema would break that assumption and
> we'd
> > > need
> > > >> > > those
> > > >> > > > tools to do assignor-specific parsing. Maybe this is OK?
> > > >> Alternatively,
> > > >> > > we
> > > >> > > > could use a separate protocol type (e.g. "compact-consumer"),
> > but
> > > >> that
> > > >> > > > seems less than desirable.
> > > >> > > >
> > > >> > > > Thanks,
> > > >> > > > Jason
> > > >> > > >
> > > >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <
> > gwen@confluent.io
> > > >
> > > >> > > wrote:
> > > >> > > >
> > > >> > > > > ah, right - we can add as many strategies as we want.
> > > >> > > > >
> > > >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <
> > > jjkoshy.w@gmail.com
> > > >> >
> > > >> > > > wrote:
> > > >> > > > >
> > > >> > > > > > > Yes it would be a protocol bump.
> > > >> > > > > > >
> > > >> > > > > >
> > > >> > > > > > Sorry - I'm officially confused. I think it may not be
> > > required
> > > >> -
> > > >> > > since
> > > >> > > > > the
> > > >> > > > > > more compact format would be associated with a new
> > assignment
> > > >> > > strategy
> > > >> > > > -
> > > >> > > > > > right?
> > > >> > > > > >
> > > >> > > > > >
> > > >> > > > > > > smaller than the plaintext PAL, but the post-compressed
> > > binary
> > > >> > PAL
> > > >> > > is
> > > >> > > > > > just
> > > >> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW
> > > using
> > > >> a
> > > >> > > > symbol
> > > >> > > > > > > table helps a lot but further compression on that
> already
> > > >> compact
> > > >> > > > > format
> > > >> > > > > > > would yield only marginal return.
> > > >> > > > > > >
> > > >> > > > > >
> > > >> > > > > > > So basically I feel we could get pretty far with a more
> > > >> compact
> > > >> > > field
> > > >> > > > > > > format for assignment and if we do that then we would
> > > >> potentially
> > > >> > > not
> > > >> > > > > > even
> > > >> > > > > > > want to do any compression.
> > > >> > > > > > >
> > > >> > > > > >
> > > >> > > > > > Also just wanted to add that this compression on the
> binary
> > > PAL
> > > >> did
> > > >> > > > help
> > > >> > > > > > but the compression ratio was obviously not as high as
> > > plaintext
> > > >> > > > > > compression.
> > > >> > > > > >
> > > >> > > > > >
> > > >> > > > > > >
> > > >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> > > >> gwen@confluent.io
> > > >> > >
> > > >> > > > > wrote:
> > > >> > > > > > >
> > > >> > > > > > >> Regarding the change to the assignment field. It would
> > be a
> > > >> > > protocol
> > > >> > > > > > bump,
> > > >> > > > > > >> otherwise consumers will not know how to parse the
> bytes
> > > the
> > > >> > > broker
> > > >> > > > is
> > > >> > > > > > >> returning, right?
> > > >> > > > > > >> Or did I misunderstand the suggestion?
> > > >> > > > > > >>
> > > >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> > > >> > > wangguoz@gmail.com>
> > > >> > > > > > >> wrote:
> > > >> > > > > > >>
> > > >> > > > > > >> > I think for just solving issue 1), Jun's suggestion
> is
> > > >> > > sufficient
> > > >> > > > > and
> > > >> > > > > > >> > simple. So I'd prefer that approach.
> > > >> > > > > > >> >
> > > >> > > > > > >> > In addition, Jason's optimization on the assignment
> > field
> > > >> > would
> > > >> > > be
> > > >> > > > > > good
> > > >> > > > > > >> for
> > > >> > > > > > >> > 2) and 3) as well, and I like that optimization for
> its
> > > >> > > simplicity
> > > >> > > > > and
> > > >> > > > > > >> no
> > > >> > > > > > >> > format change as well. And in the future I'm in favor
> > of
> > > >> > > > considering
> > > >> > > > > > to
> > > >> > > > > > >> > change the in-memory cache format as Jiangjie
> > suggested.
> > > >> > > > > > >> >
> > > >> > > > > > >> > Guozhang
> > > >> > > > > > >> >
> > > >> > > > > > >> >
> > > >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> > > >> > > > becket.qin@gmail.com>
> > > >> > > > > > >> wrote:
> > > >> > > > > > >> >
> > > >> > > > > > >> > > Hi Jason,
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > There are a few problems we want to solve here:
> > > >> > > > > > >> > > 1. The group metadata is too big to be appended to
> > the
> > > >> log.
> > > >> > > > > > >> > > 2. Reduce the memory footprint on the broker
> > > >> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > To solve (1), I like your idea of having separate
> > > >> messages
> > > >> > per
> > > >> > > > > > member.
> > > >> > > > > > >> > The
> > > >> > > > > > >> > > proposal (Onur's option 8) is to break metadata
> into
> > > >> small
> > > >> > > > records
> > > >> > > > > > in
> > > >> > > > > > >> the
> > > >> > > > > > >> > > same uncompressed message set so each record is
> > small.
> > > I
> > > >> > agree
> > > >> > > > it
> > > >> > > > > > >> would
> > > >> > > > > > >> > be
> > > >> > > > > > >> > > ideal if we are able to store the metadata
> separately
> > > for
> > > >> > each
> > > >> > > > > > >> member. I
> > > >> > > > > > >> > > was also thinking about storing the metadata into
> > > >> multiple
> > > >> > > > > messages,
> > > >> > > > > > >> too.
> > > >> > > > > > >> > > What concerns me was that having multiple messages
> > > seems
> > > >> > > > breaking
> > > >> > > > > > the
> > > >> > > > > > >> > > atomicity. I am not sure how we are going to deal
> > with
> > > >> the
> > > >> > > > > potential
> > > >> > > > > > >> > > issues. For example, What if group metadata is
> > > replicated
> > > >> > but
> > > >> > > > the
> > > >> > > > > > >> member
> > > >> > > > > > >> > > metadata is not? It might be fine depending on the
> > > >> > > > implementation
> > > >> > > > > > >> though,
> > > >> > > > > > >> > > but I am not sure.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > For (2) we want to store the metadata onto the
> disk,
> > > >> which
> > > >> > is
> > > >> > > > what
> > > >> > > > > > we
> > > >> > > > > > >> > have
> > > >> > > > > > >> > > to do anyway. The only question is in what format
> > > should
> > > >> we
> > > >> > > > store
> > > >> > > > > > >> them.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > To address (3) we want to have the metadata to be
> > > >> > compressed,
> > > >> > > > > which
> > > >> > > > > > is
> > > >> > > > > > >> > > contradict to the the above solution of (1).
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > I think Jun's suggestion is probably still the
> > > simplest.
> > > >> To
> > > >> > > > avoid
> > > >> > > > > > >> > changing
> > > >> > > > > > >> > > the behavior for consumers, maybe we can do that
> only
> > > for
> > > >> > > > > > >> offset_topic,
> > > >> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is
> > > >> smaller
> > > >> > > than
> > > >> > > > > the
> > > >> > > > > > >> > > message size on the offset topic, we always return
> at
> > > >> least
> > > >> > > one
> > > >> > > > > full
> > > >> > > > > > >> > > message. This should avoid the unexpected problem
> on
> > > the
> > > >> > > client
> > > >> > > > > side
> > > >> > > > > > >> > > because supposedly only tools and brokers will
> fetch
> > > from
> > > >> > the
> > > >> > > > the
> > > >> > > > > > >> > internal
> > > >> > > > > > >> > > topics,
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > As a modification to what you suggested, one
> > solution I
> > > >> was
> > > >> > > > > thinking
> > > >> > > > > > >> was
> > > >> > > > > > >> > to
> > > >> > > > > > >> > > have multiple messages in a single compressed
> > message.
> > > >> That
> > > >> > > > means
> > > >> > > > > > for
> > > >> > > > > > >> > > SyncGroupResponse we still need to read the entire
> > > >> > compressed
> > > >> > > > > > messages
> > > >> > > > > > >> > and
> > > >> > > > > > >> > > extract the inner messages, which seems not quite
> > > >> different
> > > >> > > from
> > > >> > > > > > >> having a
> > > >> > > > > > >> > > single message containing everything. But let me
> just
> > > >> put it
> > > >> > > > here
> > > >> > > > > > and
> > > >> > > > > > >> see
> > > >> > > > > > >> > > if that makes sense.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > We can have a map of GroupMetadataKey ->
> > > >> > > > GroupMetadataValueOffset.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > The GroupMetadataValue is stored in a compressed
> > > message.
> > > >> > The
> > > >> > > > > inner
> > > >> > > > > > >> > > messages are the following:
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > Inner Message 0: Version GroupId Generation
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can
> > > >> compress
> > > >> > > the
> > > >> > > > > > bytes
> > > >> > > > > > >> > here)
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> > > >> > > > > > >> > > ....
> > > >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > The MemberMetadata format is the following:
> > > >> > > > > > >> > >   MemberMetadata => Version Generation ClientId
> Host
> > > >> > > > Subscription
> > > >> > > > > > >> > > Assignment
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > So DescribeGroupResponse will just return the
> entire
> > > >> > > compressed
> > > >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return
> > the
> > > >> > > > > > corresponding
> > > >> > > > > > >> > inner
> > > >> > > > > > >> > > message.
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > Thanks,
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > Jiangjie (Becket) Qin
> > > >> > > > > > >> > >
> > > >> > > > > > >> > >
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson <
> > > >> > > > > > jason@confluent.io>
> > > >> > > > > > >> > > wrote:
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > > Hey Becket,
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > I like your idea to store only the offset for the
> > > group
> > > >> > > > metadata
> > > >> > > > > > in
> > > >> > > > > > >> > > memory.
> > > >> > > > > > >> > > > I think it would be safe to keep it in memory
> for a
> > > >> short
> > > >> > > time
> > > >> > > > > > after
> > > >> > > > > > >> > the
> > > >> > > > > > >> > > > rebalance completes, but after that, it's only
> real
> > > >> > purpose
> > > >> > > is
> > > >> > > > > to
> > > >> > > > > > >> > answer
> > > >> > > > > > >> > > > DescribeGroup requests, so your proposal makes a
> > lot
> > > of
> > > >> > > sense
> > > >> > > > to
> > > >> > > > > > me.
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > As for the specific problem with the size of the
> > > group
> > > >> > > > metadata
> > > >> > > > > > >> message
> > > >> > > > > > >> > > for
> > > >> > > > > > >> > > > the MM case, if we cannot succeed in reducing the
> > > size
> > > >> of
> > > >> > > the
> > > >> > > > > > >> > > > subscription/assignment (which I think is still
> > > >> probably
> > > >> > the
> > > >> > > > > best
> > > >> > > > > > >> > > > alternative if it can work), then I think there
> are
> > > >> some
> > > >> > > > options
> > > >> > > > > > for
> > > >> > > > > > >> > > > changing the message format (option #8 in Onur's
> > > >> initial
> > > >> > > > > e-mail).
> > > >> > > > > > >> > > > Currently, the key used for storing the group
> > > metadata
> > > >> is
> > > >> > > > this:
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > GroupMetadataKey => Version GroupId
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > And the value is something like this (some
> details
> > > >> > elided):
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation
> > > >> > > > > [MemberMetadata]
> > > >> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
> > > >> Assignment
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > I don't think we can change the key without a lot
> > of
> > > >> pain,
> > > >> > > but
> > > >> > > > > it
> > > >> > > > > > >> seems
> > > >> > > > > > >> > > > like we can change the value format. Maybe we can
> > > take
> > > >> the
> > > >> > > > > > >> > > > subscription/assignment payloads out of the value
> > and
> > > >> > > > introduce
> > > >> > > > > a
> > > >> > > > > > >> new
> > > >> > > > > > >> > > > "MemberMetadata" message for each member in the
> > > group.
> > > >> For
> > > >> > > > > > example:
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > MemberMetadataValue => Version Generation
> ClientId
> > > Host
> > > >> > > > > > Subscription
> > > >> > > > > > >> > > > Assignment
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > When a new generation is created, we would first
> > > write
> > > >> the
> > > >> > > > group
> > > >> > > > > > >> > metadata
> > > >> > > > > > >> > > > message which includes the generation and all of
> > the
> > > >> > > > memberIds,
> > > >> > > > > > and
> > > >> > > > > > >> > then
> > > >> > > > > > >> > > > we'd write the member metadata messages. To
> answer
> > > the
> > > >> > > > > > DescribeGroup
> > > >> > > > > > >> > > > request, we'd read the group metadata at the
> cached
> > > >> offset
> > > >> > > > and,
> > > >> > > > > > >> > depending
> > > >> > > > > > >> > > > on the version, all of the following member
> > metadata.
> > > >> This
> > > >> > > > would
> > > >> > > > > > be
> > > >> > > > > > >> > more
> > > >> > > > > > >> > > > complex to maintain, but it seems doable if it
> > comes
> > > to
> > > >> > it.
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > Thanks,
> > > >> > > > > > >> > > > Jason
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> > > >> > > > > becket.qin@gmail.com
> > > >> > > > > > >
> > > >> > > > > > >> > > wrote:
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > > It might worth thinking a little further. We
> have
> > > >> > > discussed
> > > >> > > > > this
> > > >> > > > > > >> > before
> > > >> > > > > > >> > > > > that we want to avoid holding all the group
> > > metadata
> > > >> in
> > > >> > > > > memory.
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > I am thinking about the following end state:
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > 1. Enable compression on the offset topic.
> > > >> > > > > > >> > > > > 2. Instead of holding the entire group metadata
> > in
> > > >> > memory
> > > >> > > on
> > > >> > > > > the
> > > >> > > > > > >> > > brokers,
> > > >> > > > > > >> > > > > each broker only keeps a [group -> Offset] map,
> > the
> > > >> > offset
> > > >> > > > > > points
> > > >> > > > > > >> to
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > message in the offset topic which holds the
> > latest
> > > >> > > metadata
> > > >> > > > of
> > > >> > > > > > the
> > > >> > > > > > >> > > group.
> > > >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the
> > offset
> > > >> topic
> > > >> > > > > > directly
> > > >> > > > > > >> > like
> > > >> > > > > > >> > > a
> > > >> > > > > > >> > > > > normal consumption, except that only exactly
> one
> > > >> message
> > > >> > > > will
> > > >> > > > > be
> > > >> > > > > > >> > > > returned.
> > > >> > > > > > >> > > > > 4. SyncGroupResponse will read the message,
> > extract
> > > >> the
> > > >> > > > > > assignment
> > > >> > > > > > >> > part
> > > >> > > > > > >> > > > and
> > > >> > > > > > >> > > > > send back the partition assignment. We can
> > compress
> > > >> the
> > > >> > > > > > partition
> > > >> > > > > > >> > > > > assignment before sends it out if we want.
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > Jiangjie (Becket) Qin
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason
> Gustafson
> > <
> > > >> > > > > > >> jason@confluent.io
> > > >> > > > > > >> > >
> > > >> > > > > > >> > > > > wrote:
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression)
> > > >> basically
> > > >> > > do
> > > >> > > > > > this?
> > > >> > > > > > >> If
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > > topic
> > > >> > > > > > >> > > > > > > is a string and the topic is repeated
> > > throughout,
> > > >> > > won't
> > > >> > > > > > >> > compression
> > > >> > > > > > >> > > > > > > basically replace all repeated instances of
> > it
> > > >> with
> > > >> > an
> > > >> > > > > index
> > > >> > > > > > >> > > > reference
> > > >> > > > > > >> > > > > to
> > > >> > > > > > >> > > > > > > the full string?
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > > Hey James, yeah, that's probably true, but
> keep
> > > in
> > > >> > mind
> > > >> > > > that
> > > >> > > > > > the
> > > >> > > > > > >> > > > > > compression happens on the broker side. It
> > would
> > > be
> > > >> > nice
> > > >> > > > to
> > > >> > > > > > >> have a
> > > >> > > > > > >> > > more
> > > >> > > > > > >> > > > > > compact representation so that get some
> benefit
> > > >> over
> > > >> > the
> > > >> > > > > wire
> > > >> > > > > > as
> > > >> > > > > > >> > > well.
> > > >> > > > > > >> > > > > This
> > > >> > > > > > >> > > > > > seems to be less of a concern here, so the
> > bigger
> > > >> > gains
> > > >> > > > are
> > > >> > > > > > >> > probably
> > > >> > > > > > >> > > > from
> > > >> > > > > > >> > > > > > reducing the number of partitions that need
> to
> > be
> > > >> > listed
> > > >> > > > > > >> > > individually.
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > > -Jason
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur
> Karaman <
> > > >> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> > > >> > > > > > >> > > > > > wrote:
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > > > When figuring out these optimizations, it's
> > > worth
> > > >> > > > keeping
> > > >> > > > > in
> > > >> > > > > > >> mind
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > > > improvements when the message is
> uncompressed
> > > vs
> > > >> > when
> > > >> > > > it's
> > > >> > > > > > >> > > > compressed.
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > When uncompressed:
> > > >> > > > > > >> > > > > > > Fixing the Assignment serialization to
> > instead
> > > >> be a
> > > >> > > > topic
> > > >> > > > > > >> index
> > > >> > > > > > >> > > into
> > > >> > > > > > >> > > > > the
> > > >> > > > > > >> > > > > > > corresponding member's subscription list
> > would
> > > >> > usually
> > > >> > > > be
> > > >> > > > > a
> > > >> > > > > > >> good
> > > >> > > > > > >> > > > thing.
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > I think the proposal is only worse when the
> > > topic
> > > >> > > names
> > > >> > > > > are
> > > >> > > > > > >> > small.
> > > >> > > > > > >> > > > The
> > > >> > > > > > >> > > > > > > Type.STRING we use in our protocol for the
> > > >> > > assignment's
> > > >> > > > > > >> > > > TOPIC_KEY_NAME
> > > >> > > > > > >> > > > > is
> > > >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so
> our
> > > >> strings
> > > >> > > are
> > > >> > > > > > first
> > > >> > > > > > >> > > > > prepended
> > > >> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > The new proposal does worse when:
> > > >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> > > >> > index_type_size
> > > >> > > > > > >> > > > > > > in other words when:
> > > >> > > > > > >> > > > > > > utf_encoded_string_payload_size <
> > > >> index_type_size -
> > > >> > 2
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > If the index type ends up being Type.INT32,
> > > then
> > > >> the
> > > >> > > > > > proposal
> > > >> > > > > > >> is
> > > >> > > > > > >> > > > worse
> > > >> > > > > > >> > > > > > when
> > > >> > > > > > >> > > > > > > the topic is length 1.
> > > >> > > > > > >> > > > > > > If the index type ends up being Type.INT64,
> > > then
> > > >> the
> > > >> > > > > > proposal
> > > >> > > > > > >> is
> > > >> > > > > > >> > > > worse
> > > >> > > > > > >> > > > > > when
> > > >> > > > > > >> > > > > > > the topic is less than length 6.
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > When compressed:
> > > >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how
> > > >> things
> > > >> > > > change
> > > >> > > > > > when
> > > >> > > > > > >> > > > > > compression
> > > >> > > > > > >> > > > > > > comes into the picture. This would be worth
> > > >> > > > investigating.
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James
> Cheng
> > <
> > > >> > > > > > >> > wushujames@gmail.com
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > > > wrote:
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
> > > >> Gustafson <
> > > >> > > > > > >> > > > jason@confluent.io>
> > > >> > > > > > >> > > > > > > > wrote:
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay
> out
> > > the
> > > >> > > > > assignment
> > > >> > > > > > >> > without
> > > >> > > > > > >> > > > > > needing
> > > >> > > > > > >> > > > > > > > to
> > > >> > > > > > >> > > > > > > > > explicitly repeat the topic? For
> example,
> > > the
> > > >> > > leader
> > > >> > > > > > could
> > > >> > > > > > >> > sort
> > > >> > > > > > >> > > > the
> > > >> > > > > > >> > > > > > > > topics
> > > >> > > > > > >> > > > > > > > > for each member and just use an integer
> > to
> > > >> > > represent
> > > >> > > > > the
> > > >> > > > > > >> > index
> > > >> > > > > > >> > > of
> > > >> > > > > > >> > > > > > each
> > > >> > > > > > >> > > > > > > > > topic within the sorted list (note this
> > > >> depends
> > > >> > on
> > > >> > > > the
> > > >> > > > > > >> > > > subscription
> > > >> > > > > > >> > > > > > > > > including the full topic list).
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]]
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other
> compression)
> > > >> > basically
> > > >> > > > do
> > > >> > > > > > >> this?
> > > >> > > > > > >> > If
> > > >> > > > > > >> > > > the
> > > >> > > > > > >> > > > > > > topic
> > > >> > > > > > >> > > > > > > > is a string and the topic is repeated
> > > >> throughout,
> > > >> > > > won't
> > > >> > > > > > >> > > compression
> > > >> > > > > > >> > > > > > > > basically replace all repeated instances
> of
> > > it
> > > >> > with
> > > >> > > an
> > > >> > > > > > index
> > > >> > > > > > >> > > > > reference
> > > >> > > > > > >> > > > > > to
> > > >> > > > > > >> > > > > > > > the full string?
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > > > -James
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > > > > You could even combine these two
> options
> > so
> > > >> that
> > > >> > > you
> > > >> > > > > > have
> > > >> > > > > > >> > only
> > > >> > > > > > >> > > 3
> > > >> > > > > > >> > > > > > > integers
> > > >> > > > > > >> > > > > > > > > for each topic assignment:
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition
> > > >> > > MaxPartition]
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > There may even be better options with a
> > > >> little
> > > >> > > more
> > > >> > > > > > >> thought.
> > > >> > > > > > >> > > All
> > > >> > > > > > >> > > > of
> > > >> > > > > > >> > > > > > > this
> > > >> > > > > > >> > > > > > > > is
> > > >> > > > > > >> > > > > > > > > just part of the client-side protocol,
> so
> > > it
> > > >> > > > wouldn't
> > > >> > > > > > >> require
> > > >> > > > > > >> > > any
> > > >> > > > > > >> > > > > > > version
> > > >> > > > > > >> > > > > > > > > bumps on the broker. What do you think?
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > Thanks,
> > > >> > > > > > >> > > > > > > > > Jason
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM,
> Guozhang
> > > >> Wang <
> > > >> > > > > > >> > > > wangguoz@gmail.com
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > > > > > wrote:
> > > >> > > > > > >> > > > > > > > >
> > > >> > > > > > >> > > > > > > > >> The original concern is that regex may
> > not
> > > >> be
> > > >> > > > > > efficiently
> > > >> > > > > > >> > > > > supported
> > > >> > > > > > >> > > > > > > > >> across-languages, but if there is a
> neat
> > > >> > > > workaround I
> > > >> > > > > > >> would
> > > >> > > > > > >> > > love
> > > >> > > > > > >> > > > > to
> > > >> > > > > > >> > > > > > > > learn.
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >> Guozhang
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM,
> Ismael
> > > >> Juma <
> > > >> > > > > > >> > > ismael@juma.me.uk
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > > > > > wrote:
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>> Having said that, as a general
> point, I
> > > >> think
> > > >> > we
> > > >> > > > > > should
> > > >> > > > > > >> > > > consider
> > > >> > > > > > >> > > > > > > > >> supporting
> > > >> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol.
> It
> > > >> > requires
> > > >> > > > > some
> > > >> > > > > > >> > > thinking
> > > >> > > > > > >> > > > > for
> > > >> > > > > > >> > > > > > > > >>> cross-language support, but it seems
> > > >> > > surmountable
> > > >> > > > > and
> > > >> > > > > > it
> > > >> > > > > > >> > > could
> > > >> > > > > > >> > > > > make
> > > >> > > > > > >> > > > > > > > >> certain
> > > >> > > > > > >> > > > > > > > >>> operations a lot more efficient (the
> > fact
> > > >> > that a
> > > >> > > > > basic
> > > >> > > > > > >> > regex
> > > >> > > > > > >> > > > > > > > subscription
> > > >> > > > > > >> > > > > > > > >>> causes the consumer to request
> metadata
> > > for
> > > >> > all
> > > >> > > > > topics
> > > >> > > > > > >> is
> > > >> > > > > > >> > not
> > > >> > > > > > >> > > > > > great).
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>> Ismael
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM,
> > > Guozhang
> > > >> > Wang
> > > >> > > <
> > > >> > > > > > >> > > > > > wangguoz@gmail.com>
> > > >> > > > > > >> > > > > > > > >>> wrote:
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing
> > the
> > > >> > > handling
> > > >> > > > > > >> logics of
> > > >> > > > > > >> > > > > single
> > > >> > > > > > >> > > > > > > > large
> > > >> > > > > > >> > > > > > > > >>>> message on the consumer side.
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>> As for the case of "a single group
> > > >> > subscribing
> > > >> > > to
> > > >> > > > > > 3000
> > > >> > > > > > >> > > > topics",
> > > >> > > > > > >> > > > > > with
> > > >> > > > > > >> > > > > > > > >> 100
> > > >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
> > > >> reasonable
> > > >> > to
> > > >> > > me
> > > >> > > > > > (when
> > > >> > > > > > >> > > > storing
> > > >> > > > > > >> > > > > in
> > > >> > > > > > >> > > > > > > ZK,
> > > >> > > > > > >> > > > > > > > >> we
> > > >> > > > > > >> > > > > > > > >>>> also have the znode limit which is
> set
> > > to
> > > >> 1Mb
> > > >> > > by
> > > >> > > > > > >> default,
> > > >> > > > > > >> > > > though
> > > >> > > > > > >> > > > > > > > >>> admittedly
> > > >> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if
> > we
> > > do
> > > >> > the
> > > >> > > > > change
> > > >> > > > > > >> as
> > > >> > > > > > >> > Jun
> > > >> > > > > > >> > > > > > > > suggested,
> > > >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure
> is
> > > OK
> > > >> I
> > > >> > > > think.
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>> Guozhang
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM,
> Onur
> > > >> > Karaman
> > > >> > > <
> > > >> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> > > >> > > > > > >> > > > > > > > >>>>> wrote:
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>>> Results without compression:
> > > >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the
> > tipping
> > > >> > point
> > > >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> > > >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> > > >> > > > > > >> > > > > > > > >>>>>
> > > >> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression
> > > shrinks
> > > >> > the
> > > >> > > > > > message
> > > >> > > > > > >> > size
> > > >> > > > > > >> > > by
> > > >> > > > > > >> > > > > 4x.
> > > >> > > > > > >> > > > > > > > >>>>>
> > > >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM,
> Jun
> > > Rao
> > > >> <
> > > >> > > > > > >> > jun@confluent.io
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > > > > > wrote:
> > > >> > > > > > >> > > > > > > > >>>>>
> > > >> > > > > > >> > > > > > > > >>>>>> Onur,
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how
> we
> > > >> deal
> > > >> > > with
> > > >> > > > > the
> > > >> > > > > > >> case
> > > >> > > > > > >> > > > when a
> > > >> > > > > > >> > > > > > > > >>> message
> > > >> > > > > > >> > > > > > > > >>>> is
> > > >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today,
> > if
> > > >> the
> > > >> > > fetch
> > > >> > > > > > size
> > > >> > > > > > >> is
> > > >> > > > > > >> > > > > smaller
> > > >> > > > > > >> > > > > > > > >> than
> > > >> > > > > > >> > > > > > > > >>>> the
> > > >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get
> > > stuck.
> > > >> > > > Instead,
> > > >> > > > > > we
> > > >> > > > > > >> can
> > > >> > > > > > >> > > > > simply
> > > >> > > > > > >> > > > > > > > >>> return
> > > >> > > > > > >> > > > > > > > >>>>> the
> > > >> > > > > > >> > > > > > > > >>>>>> full message if it's larger than
> the
> > > >> fetch
> > > >> > > size
> > > >> > > > > w/o
> > > >> > > > > > >> > > > requiring
> > > >> > > > > > >> > > > > > the
> > > >> > > > > > >> > > > > > > > >>>>> consumer
> > > >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size.
> > On
> > > >> the
> > > >> > > > broker
> > > >> > > > > > >> side,
> > > >> > > > > > >> > to
> > > >> > > > > > >> > > > > serve
> > > >> > > > > > >> > > > > > a
> > > >> > > > > > >> > > > > > > > >>> fetch
> > > >> > > > > > >> > > > > > > > >>>>>> request, we already do an index
> > lookup
> > > >> and
> > > >> > > then
> > > >> > > > > > scan
> > > >> > > > > > >> the
> > > >> > > > > > >> > > > log a
> > > >> > > > > > >> > > > > > bit
> > > >> > > > > > >> > > > > > > > >> to
> > > >> > > > > > >> > > > > > > > >>>>> find
> > > >> > > > > > >> > > > > > > > >>>>>> the message with the requested
> > offset.
> > > >> We
> > > >> > can
> > > >> > > > > just
> > > >> > > > > > >> check
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > > size
> > > >> > > > > > >> > > > > > > > >> of
> > > >> > > > > > >> > > > > > > > >>>> that
> > > >> > > > > > >> > > > > > > > >>>>>> message and return the full
> message
> > if
> > > >> its
> > > >> > > size
> > > >> > > > > is
> > > >> > > > > > >> > larger
> > > >> > > > > > >> > > > than
> > > >> > > > > > >> > > > > > the
> > > >> > > > > > >> > > > > > > > >>>> fetch
> > > >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is
> really
> > > for
> > > >> > > > > > performance
> > > >> > > > > > >> > > > > > optimization,
> > > >> > > > > > >> > > > > > > > >>> i.e.
> > > >> > > > > > >> > > > > > > > >>>>> in
> > > >> > > > > > >> > > > > > > > >>>>>> the common case, we will not
> return
> > > more
> > > >> > > bytes
> > > >> > > > > than
> > > >> > > > > > >> > fetch
> > > >> > > > > > >> > > > > size,
> > > >> > > > > > >> > > > > > > but
> > > >> > > > > > >> > > > > > > > >>> if
> > > >> > > > > > >> > > > > > > > >>>>>> there is a large message, we will
> > > return
> > > >> > more
> > > >> > > > > bytes
> > > >> > > > > > >> than
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > > > > >>> specified
> > > >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large
> > > messages
> > > >> are
> > > >> > > > rare.
> > > >> > > > > > >> So, it
> > > >> > > > > > >> > > > > > shouldn't
> > > >> > > > > > >> > > > > > > > >>>>> increase
> > > >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the
> client
> > > too
> > > >> > > much.
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>> Jun
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM,
> > Onur
> > > >> > > Karaman <
> > > >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> > > >> > > > > > >> > > > > > > > >>>>>> wrote:
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing
> > some
> > > >> > tests
> > > >> > > on
> > > >> > > > > the
> > > >> > > > > > >> new
> > > >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> > > >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more
> > > >> strenuous
> > > >> > use
> > > >> > > > > cases
> > > >> > > > > > >> like
> > > >> > > > > > >> > > > > > mirroring
> > > >> > > > > > >> > > > > > > > >>>>>> clusters
> > > >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and
> > thought
> > > >> I'd
> > > >> > > share
> > > >> > > > > > >> > whatever I
> > > >> > > > > > >> > > > > have
> > > >> > > > > > >> > > > > > so
> > > >> > > > > > >> > > > > > > > >>>> far.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount
> > of
> > > >> group
> > > >> > > > > > metadata
> > > >> > > > > > >> we
> > > >> > > > > > >> > > can
> > > >> > > > > > >> > > > > fit
> > > >> > > > > > >> > > > > > > > >> into
> > > >> > > > > > >> > > > > > > > >>>> one
> > > >> > > > > > >> > > > > > > > >>>>>>> message
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Some background:
> > > >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is
> > implemented
> > > >> in
> > > >> > two
> > > >> > > > > > phases
> > > >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase
> that
> > > >> > > identifies
> > > >> > > > > > >> members
> > > >> > > > > > >> > of
> > > >> > > > > > >> > > > the
> > > >> > > > > > >> > > > > > > > >> group
> > > >> > > > > > >> > > > > > > > >>>> and
> > > >> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions.
> > > >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that
> waits
> > > for
> > > >> > the
> > > >> > > > > group
> > > >> > > > > > >> > leader
> > > >> > > > > > >> > > to
> > > >> > > > > > >> > > > > > > > >> decide
> > > >> > > > > > >> > > > > > > > >>>>> member
> > > >> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
> > > >> > > subscriptions
> > > >> > > > > > across
> > > >> > > > > > >> > the
> > > >> > > > > > >> > > > > group.
> > > >> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this
> > decision
> > > >> > with a
> > > >> > > > > > >> > > > > SyncGroupRequest.
> > > >> > > > > > >> > > > > > > > >> The
> > > >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> > > >> SyncGroupRequests
> > > >> > > by
> > > >> > > > > > >> appending
> > > >> > > > > > >> > > all
> > > >> > > > > > >> > > > > > group
> > > >> > > > > > >> > > > > > > > >>>> state
> > > >> > > > > > >> > > > > > > > >>>>>>> into a single message under the
> > > >> > > > > __consumer_offsets
> > > >> > > > > > >> > topic.
> > > >> > > > > > >> > > > > This
> > > >> > > > > > >> > > > > > > > >>>> message
> > > >> > > > > > >> > > > > > > > >>>>> is
> > > >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and
> contains
> > > each
> > > >> > > member
> > > >> > > > > > >> > > subscription
> > > >> > > > > > >> > > > > as
> > > >> > > > > > >> > > > > > > > >> well
> > > >> > > > > > >> > > > > > > > >>>> as
> > > >> > > > > > >> > > > > > > > >>>>>> the
> > > >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each
> member.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> The environment:
> > > >> > > > > > >> > > > > > > > >>>>>>> - one broker
> > > >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets
> partition
> > > >> > > > > > >> > > > > > > > >>>>>>> -
> offsets.topic.compression.codec=1
> > > //
> > > >> > this
> > > >> > > is
> > > >> > > > > > gzip
> > > >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending
> KAFKA-3718
> > > >> patch
> > > >> > > that
> > > >> > > > > > >> actually
> > > >> > > > > > >> > > > makes
> > > >> > > > > > >> > > > > > use
> > > >> > > > > > >> > > > > > > > >> of
> > > >> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec:
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> https://github.com/apache/kafka/pull/1394
> > > >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an
> > > actual
> > > >> > > subset
> > > >> > > > > of
> > > >> > > > > > >> > topics
> > > >> > > > > > >> > > > from
> > > >> > > > > > >> > > > > > one
> > > >> > > > > > >> > > > > > > > >>> of
> > > >> > > > > > >> > > > > > > > >>>>> our
> > > >> > > > > > >> > > > > > > > >>>>>>> clusters.
> > > >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> > > >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long
> on
> > > >> average
> > > >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number
> > of
> > > >> > > consumers
> > > >> > > > > > each
> > > >> > > > > > >> > > > hardcoded
> > > >> > > > > > >> > > > > > > > >> with
> > > >> > > > > > >> > > > > > > > >>>> all
> > > >> > > > > > >> > > > > > > > >>>>>> the
> > > >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests
> more
> > > >> > > consistent.
> > > >> > > > > > >> > > wildcarding
> > > >> > > > > > >> > > > > with
> > > >> > > > > > >> > > > > > > > >> .*
> > > >> > > > > > >> > > > > > > > >>>>> should
> > > >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> > > >> subscription
> > > >> > > > hits
> > > >> > > > > > the
> > > >> > > > > > >> > > > > coordinator
> > > >> > > > > > >> > > > > > > > >> as
> > > >> > > > > > >> > > > > > > > >>>> the
> > > >> > > > > > >> > > > > > > > >>>>>>> subscription has already been
> fully
> > > >> > expanded
> > > >> > > > out
> > > >> > > > > > to
> > > >> > > > > > >> the
> > > >> > > > > > >> > > > list
> > > >> > > > > > >> > > > > of
> > > >> > > > > > >> > > > > > > > >>>> topics
> > > >> > > > > > >> > > > > > > > >>>>> by
> > > >> > > > > > >> > > > > > > > >>>>>>> the consumers.
> > > >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to
> > > >> Log.scala
> > > >> > to
> > > >> > > > > print
> > > >> > > > > > >> out
> > > >> > > > > > >> > the
> > > >> > > > > > >> > > > > > message
> > > >> > > > > > >> > > > > > > > >>>> sizes
> > > >> > > > > > >> > > > > > > > >>>>>>> after compression
> > > >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all
> and
> > > >> auto
> > > >> > > > commits
> > > >> > > > > > are
> > > >> > > > > > >> > > > > disabled.
> > > >> > > > > > >> > > > > > > > >> The
> > > >> > > > > > >> > > > > > > > >>>> only
> > > >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added
> > is
> > > >> the
> > > >> > > > > > >> > > __consumer_offsets
> > > >> > > > > > >> > > > > > topic
> > > >> > > > > > >> > > > > > > > >>> and
> > > >> > > > > > >> > > > > > > > >>>>>>> they're only from storing group
> > > >> metadata
> > > >> > > while
> > > >> > > > > > >> > processing
> > > >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Results:
> > > >> > > > > > >> > > > > > > > >>>>>>> The results below show that we
> > exceed
> > > >> the
> > > >> > > > > 1000012
> > > >> > > > > > >> byte
> > > >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit
> > > >> > relatively
> > > >> > > > > > quickly
> > > >> > > > > > >> > > > (between
> > > >> > > > > > >> > > > > > > > >> 30-40
> > > >> > > > > > >> > > > > > > > >>>>>>> consumers):
> > > >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the
> > > >> tipping
> > > >> > > point
> > > >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is
> > pretty
> > > >> > > gradual.
> > > >> > > > > > >> Plotting
> > > >> > > > > > >> > > the
> > > >> > > > > > >> > > > > > > > >> points
> > > >> > > > > > >> > > > > > > > >>>>> makes
> > > >> > > > > > >> > > > > > > > >>>>>> it
> > > >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the
> > number
> > > of
> > > >> > > > > consumers:
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > >
> > > >> > > > > > >> >
> > > >> > > > > > >>
> > > >> > > > > >
> > > >> > > > >
> > > >> > > >
> > > >> > >
> > > >> >
> > > >>
> > >
> >
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers
> aren't
> > > >> > averages
> > > >> > > > or
> > > >> > > > > > >> medians
> > > >> > > > > > >> > > or
> > > >> > > > > > >> > > > > > > > >> anything
> > > >> > > > > > >> > > > > > > > >>>>> like
> > > >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size
> from
> > a
> > > >> given
> > > >> > > > run.
> > > >> > > > > I
> > > >> > > > > > >> did
> > > >> > > > > > >> > run
> > > >> > > > > > >> > > > > them
> > > >> > > > > > >> > > > > > a
> > > >> > > > > > >> > > > > > > > >>> few
> > > >> > > > > > >> > > > > > > > >>>>>> times
> > > >> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Impact:
> > > >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> > > >> > > > __consumer_offsets
> > > >> > > > > > >> topic
> > > >> > > > > > >> > > with
> > > >> > > > > > >> > > > > my
> > > >> > > > > > >> > > > > > > > >>>> pending
> > > >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the
> AwaitingSync
> > > >> phase
> > > >> > of
> > > >> > > > the
> > > >> > > > > > >> group
> > > >> > > > > > >> > > fails
> > > >> > > > > > >> > > > > > with
> > > >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This
> means
> > > the
> > > >> > > > combined
> > > >> > > > > > >> size
> > > >> > > > > > >> > of
> > > >> > > > > > >> > > > each
> > > >> > > > > > >> > > > > > > > >>>> member's
> > > >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments
> > > exceeded
> > > >> the
> > > >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> > > >> > > > > > >> > > > > > > > >>>>> of
> > > >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up
> > > dying.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Options:
> > > >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the
> number
> > > of
> > > >> > > > consumers
> > > >> > > > > > in
> > > >> > > > > > >> the
> > > >> > > > > > >> > > > > group.
> > > >> > > > > > >> > > > > > > > >> This
> > > >> > > > > > >> > > > > > > > >>>>> isn't
> > > >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more
> > > >> > strenuous
> > > >> > > > use
> > > >> > > > > > >> cases
> > > >> > > > > > >> > > like
> > > >> > > > > > >> > > > > > > > >>>> MirrorMaker
> > > >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> > > >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group
> > > into
> > > >> > > smaller
> > > >> > > > > > >> groups
> > > >> > > > > > >> > > which
> > > >> > > > > > >> > > > > > > > >>> together
> > > >> > > > > > >> > > > > > > > >>>>> will
> > > >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics.
> > This
> > > >> > gives
> > > >> > > > each
> > > >> > > > > > >> group
> > > >> > > > > > >> > > > > member a
> > > >> > > > > > >> > > > > > > > >>>> smaller
> > > >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics
> > > >> starting
> > > >> > > with
> > > >> > > > > a-m
> > > >> > > > > > >> while
> > > >> > > > > > >> > > g2
> > > >> > > > > > >> > > > > has
> > > >> > > > > > >> > > > > > > > >>> topics
> > > >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be
> > > >> > > operationally
> > > >> > > > > > >> painful
> > > >> > > > > > >> > to
> > > >> > > > > > >> > > > > > manage.
> > > >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the
> topics
> > > >> among
> > > >> > > > members
> > > >> > > > > > of
> > > >> > > > > > >> the
> > > >> > > > > > >> > > > > group.
> > > >> > > > > > >> > > > > > > > >>> Again
> > > >> > > > > > >> > > > > > > > >>>>> this
> > > >> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller
> > > >> > > > subscription.
> > > >> > > > > > This
> > > >> > > > > > >> > > would
> > > >> > > > > > >> > > > > also
> > > >> > > > > > >> > > > > > > > >> be
> > > >> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage.
> > > >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> > > >> > > > > > >> KafkaConfig.messageMaxBytes
> > > >> > > > > > >> > (a
> > > >> > > > > > >> > > > > > > > >>> topic-level
> > > >> > > > > > >> > > > > > > > >>>>>>> config) and
> > > >> > KafkaConfig.replicaFetchMaxBytes
> > > >> > > > (a
> > > >> > > > > > >> > > > broker-level
> > > >> > > > > > >> > > > > > > > >>> config).
> > > >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just
> > the
> > > >> > > > > > >> __consumer_offsets
> > > >> > > > > > >> > > > topic
> > > >> > > > > > >> > > > > > > > >> seems
> > > >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping
> up
> > > the
> > > >> > > > > > broker-level
> > > >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> > > >> > > > > > >> > > > > > > > >>>>>>> would probably need more
> attention.
> > > >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
> > > >> > compression
> > > >> > > > > > codecs.
> > > >> > > > > > >> > Based
> > > >> > > > > > >> > > > on
> > > >> > > > > > >> > > > > 2
> > > >> > > > > > >> > > > > > > > >>>> minutes
> > > >> > > > > > >> > > > > > > > >>>>> of
> > > >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and
> > > snappy
> > > >> are
> > > >> > > > > faster
> > > >> > > > > > >> than
> > > >> > > > > > >> > > gzip
> > > >> > > > > > >> > > > > but
> > > >> > > > > > >> > > > > > > > >>> have
> > > >> > > > > > >> > > > > > > > >>>>>> worse
> > > >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably
> won't
> > > >> help.
> > > >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support
> > > >> sending
> > > >> > > the
> > > >> > > > > > regex
> > > >> > > > > > >> > over
> > > >> > > > > > >> > > > the
> > > >> > > > > > >> > > > > > wire
> > > >> > > > > > >> > > > > > > > >>>>> instead
> > > >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> > > >> > subscriptions. I
> > > >> > > > > think
> > > >> > > > > > >> > people
> > > >> > > > > > >> > > > > said
> > > >> > > > > > >> > > > > > in
> > > >> > > > > > >> > > > > > > > >>> the
> > > >> > > > > > >> > > > > > > > >>>>>> past
> > > >> > > > > > >> > > > > > > > >>>>>>> that different languages have
> > subtle
> > > >> > > > differences
> > > >> > > > > > in
> > > >> > > > > > >> > > regex,
> > > >> > > > > > >> > > > so
> > > >> > > > > > >> > > > > > > > >> this
> > > >> > > > > > >> > > > > > > > >>>>>> doesn't
> > > >> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language
> > > groups.
> > > >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe
> we
> > > can
> > > >> > > reverse
> > > >> > > > > the
> > > >> > > > > > >> > > mapping?
> > > >> > > > > > >> > > > > > > > >> Instead
> > > >> > > > > > >> > > > > > > > >>>> of
> > > >> > > > > > >> > > > > > > > >>>>>>> mapping from member to
> > subscriptions,
> > > >> we
> > > >> > can
> > > >> > > > > map a
> > > >> > > > > > >> > > > > subscription
> > > >> > > > > > >> > > > > > > > >> to
> > > >> > > > > > >> > > > > > > > >>> a
> > > >> > > > > > >> > > > > > > > >>>>> list
> > > >> > > > > > >> > > > > > > > >>>>>>> of members.
> > > >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe
> we
> > > can
> > > >> try
> > > >> > > to
> > > >> > > > > > break
> > > >> > > > > > >> > apart
> > > >> > > > > > >> > > > the
> > > >> > > > > > >> > > > > > > > >>>>>> subscription
> > > >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> > > >> > > SyncGroupRequest
> > > >> > > > > > into
> > > >> > > > > > >> > > > multiple
> > > >> > > > > > >> > > > > > > > >>> records?
> > > >> > > > > > >> > > > > > > > >>>>>> They
> > > >> > > > > > >> > > > > > > > >>>>>>> can still go to the same message
> > set
> > > >> and
> > > >> > get
> > > >> > > > > > >> appended
> > > >> > > > > > >> > > > > together.
> > > >> > > > > > >> > > > > > > > >>> This
> > > >> > > > > > >> > > > > > > > >>>>> way
> > > >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment
> size,
> > > >> which
> > > >> > > > > shouldn't
> > > >> > > > > > >> be a
> > > >> > > > > > >> > > > > > problem.
> > > >> > > > > > >> > > > > > > > >>> This
> > > >> > > > > > >> > > > > > > > >>>>> can
> > > >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because
> > we're
> > > >> > > currently
> > > >> > > > > > >> keying
> > > >> > > > > > >> > > these
> > > >> > > > > > >> > > > > > > > >>> messages
> > > >> > > > > > >> > > > > > > > >>>> on
> > > >> > > > > > >> > > > > > > > >>>>>> the
> > > >> > > > > > >> > > > > > > > >>>>>>> group, so I think records from
> the
> > > same
> > > >> > > > > rebalance
> > > >> > > > > > >> might
> > > >> > > > > > >> > > > > > > > >>> accidentally
> > > >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> > > >> understanding
> > > >> > of
> > > >> > > > > > >> compaction
> > > >> > > > > > >> > > > isn't
> > > >> > > > > > >> > > > > > > > >> that
> > > >> > > > > > >> > > > > > > > >>>>> great.
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> Todo:
> > > >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun
> > the
> > > >> tests
> > > >> > > > with
> > > >> > > > > no
> > > >> > > > > > >> > > > > compression
> > > >> > > > > > >> > > > > > > > >> just
> > > >> > > > > > >> > > > > > > > >>>> to
> > > >> > > > > > >> > > > > > > > >>>>>> see
> > > >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's
> > > >> getting
> > > >> > > > late.
> > > >> > > > > > >> Maybe
> > > >> > > > > > >> > > > > tomorrow?
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>> - Onur
> > > >> > > > > > >> > > > > > > > >>>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>>
> > > >> > > > > > >> > > > > > > > >>>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>> --
> > > >> > > > > > >> > > > > > > > >>>> -- Guozhang
> > > >> > > > > > >> > > > > > > > >>>>
> > > >> > > > > > >> > > > > > > > >>>
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > > >> --
> > > >> > > > > > >> > > > > > > > >> -- Guozhang
> > > >> > > > > > >> > > > > > > > >>
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > > >
> > > >> > > > > > >> > > > > > >
> > > >> > > > > > >> > > > > >
> > > >> > > > > > >> > > > >
> > > >> > > > > > >> > > >
> > > >> > > > > > >> > >
> > > >> > > > > > >> >
> > > >> > > > > > >> >
> > > >> > > > > > >> >
> > > >> > > > > > >> > --
> > > >> > > > > > >> > -- Guozhang
> > > >> > > > > > >> >
> > > >> > > > > > >>
> > > >> > > > > > >
> > > >> > > > > > >
> > > >> > > > > >
> > > >> > > > >
> > > >> > > >
> > > >> > >
> > > >> >
> > > >>
> > > >
> > > >
> > >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Onur Karaman <ok...@linkedin.com.INVALID>]

I think the value of adding a "offsets.replica.fetch.max.bytes" config is
that we don't break/change the meaning of "replica.fetch.max.bytes".

We can also set "offsets.replica.fetch.max.bytes" to be a value safely
larger than what we expect to ever allow the __consumer_offsets topic max
message size to be without doing the larger change of bumping up the global
"replica.fetch.max.bytes".

On Thu, Jun 9, 2016 at 10:40 AM, Becket Qin <be...@gmail.com> wrote:

> I think taking bigger one of the fetch size and message size limit is
> probably good enough. If we have a separate
> "offset.replica.fetch.max.bytes", I guess the value will always be set to
> max message size of the __consumer_offsets topic, which does not seem to
> have much value.
>
> On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman <okaraman@linkedin.com.invalid
> >
> wrote:
>
> > Maybe another approach can be to add a new
> > "offsets.replica.fetch.max.bytes" config on the brokers.
> >
> > On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <ok...@linkedin.com>
> > wrote:
> >
> > > I made a PR with a tweak to Jun's/Becket's proposal:
> > > https://github.com/apache/kafka/pull/1484
> > >
> > > It just tweaks the fetch behavior specifically for replicas fetching
> from
> > > the __consumer_offsets topic when the fetcher's
> "replica.fetch.max.bytes"
> > > is less than the __consumer_offset leader's "message.max.bytes" to take
> > the
> > > max of the two.
> > >
> > > I'm honestly not that happy with this solution, as I'd rather not
> change
> > > the "replica.fetch.max.bytes" config from being a limit to a
> > > recommendation. I'd definitely be happy to hear other alternatives!
> > >
> > > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> > > onurkaraman.apache@gmail.com> wrote:
> > >
> > >> Sorry I know next to nothing about Kafka Connect. I didn't understand
> > the
> > >> Kafka Connect / MM idea you brought up. Can you go into more detail?
> > >>
> > >> Otherwise I think our remaining options are:
> > >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
> > >> __consumer_offsets topic and change the fetch behavior when message
> size
> > >> is
> > >> larger than fetch size
> > >> - option 6: support sending the regex over the wire instead of the
> fully
> > >> expanded topic subscriptions. This should cut down the message size
> from
> > >> the subscription side. Again this only helps when pattern-based
> > >> subscriptions are done.
> > >>
> > >> minor correction to an earlier comment I made regarding the message
> > size:
> > >> message size ~ sum(s_i + a_i for i in range [1, |C|])
> > >>
> > >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <ja...@confluent.io>
> > >> wrote:
> > >>
> > >> > Hey Onur,
> > >> >
> > >> > Thanks for the investigation. It seems the conclusion is that the
> > >> compact
> > >> > format helps, but perhaps not enough to justify adding a new
> > assignment
> > >> > schema? I'm not sure there's much more room for savings unless we
> > change
> > >> > something more fundamental in the assignment approach. We spent some
> > >> time
> > >> > thinking before about whether we could let the consumers compute
> their
> > >> > assignment locally from a smaller set of information, but the
> > difficulty
> > >> > (I'm sure you remember) is reaching consensus on topic metadata.
> Kafka
> > >> > Connect has a similar problem where all the workers need to agree on
> > >> > connector configurations. Since all configs are stored in a single
> > topic
> > >> > partition, the approach we take there is to propagate the offset in
> > the
> > >> > assignment protocol. Not sure if we could do something similar for
> > MM...
> > >> > Anyway, it seems like the best workaround at the moment is Jun's
> > initial
> > >> > suggestion. What do you think?
> > >> >
> > >> > -Jason
> > >> >
> > >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> > >> > onurkaraman.apache@gmail.com
> > >> > > wrote:
> > >> >
> > >> > > I gave the topic index assignment trick a try against the same
> > >> > environment.
> > >> > > The implementation just changed the assignment serialization and
> > >> > > deserialization logic. It didn't change SyncGroupResponse, meaning
> > it
> > >> > > continues to exclude the subscription from the SyncGroupResponse
> and
> > >> > > assumes the member has kept track of its last subscription.
> > >> > >
> > >> > > Assignment topic indexing with compression:
> > >> > > 1 consumer 34346 bytes
> > >> > > 5 consumers 177687 bytes
> > >> > > 10 consumers 331897 bytes
> > >> > > 20 consumers 572467 bytes
> > >> > > 30 consumers 811269 bytes
> > >> > > 40 consumers 1047188 bytes * the tipping point
> > >> > > 50 consumers 1290092 bytes
> > >> > > 60 consumers 1527806 bytes
> > >> > > 70 consumers 1769259 bytes
> > >> > > 80 consumers 2000118 bytes
> > >> > > 90 consumers 2244392 bytes
> > >> > > 100 consumers 2482415 bytes
> > >> > >
> > >> > > Assignment topic indexing without compression:
> > >> > > 1 consumer 211904 bytes
> > >> > > 5 consumers 677184 bytes
> > >> > > 10 consumers 1211154 bytes * the tipping point
> > >> > > 20 consumers 2136196 bytes
> > >> > > 30 consumers 3061238 bytes
> > >> > > 40 consumers 3986280 bytes
> > >> > > 50 consumers 4911322 bytes
> > >> > > 60 consumers 5836284 bytes
> > >> > > 70 consumers 6761246 bytes
> > >> > > 80 consumers 7686208 bytes
> > >> > > 90 consumers 8611170 bytes
> > >> > > 100 consumers 9536132 bytes
> > >> > >
> > >> > > Assignment topic indexing seems to reduce the size by 500KB
> without
> > >> > > compression and 80KB with compression. So assignment topic
> indexing
> > >> makes
> > >> > > some difference in both with and without compression but in our
> case
> > >> was
> > >> > > not nearly enough.
> > >> > >
> > >> > > This can be explained by the fact that we aren't actually hitting
> > the
> > >> > worst
> > >> > > case scenario of each consumer being assigned a partition from
> every
> > >> > topic.
> > >> > > The reason is simple: a topic can only fully span all the
> consumers
> > >> if it
> > >> > > has at least as many partitions as there are consumers. Given that
> > >> there
> > >> > > are 8 partitions per topic and we have 100 consumers, it makes
> sense
> > >> that
> > >> > > we aren't close to this worse case scenario where topic indexing
> > would
> > >> > make
> > >> > > a bigger difference.
> > >> > >
> > >> > > I tweaked the group leader's assignment code to print out the
> > >> assignments
> > >> > > and found that each consumer was getting either 238 or 239
> > partitions.
> > >> > Each
> > >> > > of these partitions were from unique topics. So the consumers were
> > >> really
> > >> > > getting partitions from 239 topics instead of the full worst case
> > >> > scenario
> > >> > > of 3000 topics.
> > >> > >
> > >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <
> > jason@confluent.io>
> > >> > > wrote:
> > >> > >
> > >> > > > Gwen, Joel:
> > >> > > >
> > >> > > > That's correct. The protocol does allow us to give an assignor
> its
> > >> own
> > >> > > > assignment schema, but I think this will require a couple
> internal
> > >> > > changes
> > >> > > > to the consumer to make use of the full generality.
> > >> > > >
> > >> > > > One thing I'm a little uncertain about is whether we should use
> a
> > >> > > different
> > >> > > > protocol type. For a little context, the group membership
> protocol
> > >> > allows
> > >> > > > the client to provide a "protocol type" when joining the group
> to
> > >> > ensure
> > >> > > > that all members have some basic semantic compatibility. For
> > >> example,
> > >> > the
> > >> > > > consumer uses "consumer" and Kafka Connect uses "connect."
> > Currently
> > >> > all
> > >> > > > assignors using the "consumer" protocol share a common schema
> for
> > >> > > > representing subscriptions and assignment. This is convenient
> for
> > >> tools
> > >> > > > (like consumer-groups.sh) since they just need to know how to
> > parse
> > >> the
> > >> > > > "consumer" protocol type without knowing anything about the
> > >> assignors.
> > >> > So
> > >> > > > introducing another schema would break that assumption and we'd
> > need
> > >> > > those
> > >> > > > tools to do assignor-specific parsing. Maybe this is OK?
> > >> Alternatively,
> > >> > > we
> > >> > > > could use a separate protocol type (e.g. "compact-consumer"),
> but
> > >> that
> > >> > > > seems less than desirable.
> > >> > > >
> > >> > > > Thanks,
> > >> > > > Jason
> > >> > > >
> > >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <
> gwen@confluent.io
> > >
> > >> > > wrote:
> > >> > > >
> > >> > > > > ah, right - we can add as many strategies as we want.
> > >> > > > >
> > >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <
> > jjkoshy.w@gmail.com
> > >> >
> > >> > > > wrote:
> > >> > > > >
> > >> > > > > > > Yes it would be a protocol bump.
> > >> > > > > > >
> > >> > > > > >
> > >> > > > > > Sorry - I'm officially confused. I think it may not be
> > required
> > >> -
> > >> > > since
> > >> > > > > the
> > >> > > > > > more compact format would be associated with a new
> assignment
> > >> > > strategy
> > >> > > > -
> > >> > > > > > right?
> > >> > > > > >
> > >> > > > > >
> > >> > > > > > > smaller than the plaintext PAL, but the post-compressed
> > binary
> > >> > PAL
> > >> > > is
> > >> > > > > > just
> > >> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW
> > using
> > >> a
> > >> > > > symbol
> > >> > > > > > > table helps a lot but further compression on that already
> > >> compact
> > >> > > > > format
> > >> > > > > > > would yield only marginal return.
> > >> > > > > > >
> > >> > > > > >
> > >> > > > > > > So basically I feel we could get pretty far with a more
> > >> compact
> > >> > > field
> > >> > > > > > > format for assignment and if we do that then we would
> > >> potentially
> > >> > > not
> > >> > > > > > even
> > >> > > > > > > want to do any compression.
> > >> > > > > > >
> > >> > > > > >
> > >> > > > > > Also just wanted to add that this compression on the binary
> > PAL
> > >> did
> > >> > > > help
> > >> > > > > > but the compression ratio was obviously not as high as
> > plaintext
> > >> > > > > > compression.
> > >> > > > > >
> > >> > > > > >
> > >> > > > > > >
> > >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> > >> gwen@confluent.io
> > >> > >
> > >> > > > > wrote:
> > >> > > > > > >
> > >> > > > > > >> Regarding the change to the assignment field. It would
> be a
> > >> > > protocol
> > >> > > > > > bump,
> > >> > > > > > >> otherwise consumers will not know how to parse the bytes
> > the
> > >> > > broker
> > >> > > > is
> > >> > > > > > >> returning, right?
> > >> > > > > > >> Or did I misunderstand the suggestion?
> > >> > > > > > >>
> > >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> > >> > > wangguoz@gmail.com>
> > >> > > > > > >> wrote:
> > >> > > > > > >>
> > >> > > > > > >> > I think for just solving issue 1), Jun's suggestion is
> > >> > > sufficient
> > >> > > > > and
> > >> > > > > > >> > simple. So I'd prefer that approach.
> > >> > > > > > >> >
> > >> > > > > > >> > In addition, Jason's optimization on the assignment
> field
> > >> > would
> > >> > > be
> > >> > > > > > good
> > >> > > > > > >> for
> > >> > > > > > >> > 2) and 3) as well, and I like that optimization for its
> > >> > > simplicity
> > >> > > > > and
> > >> > > > > > >> no
> > >> > > > > > >> > format change as well. And in the future I'm in favor
> of
> > >> > > > considering
> > >> > > > > > to
> > >> > > > > > >> > change the in-memory cache format as Jiangjie
> suggested.
> > >> > > > > > >> >
> > >> > > > > > >> > Guozhang
> > >> > > > > > >> >
> > >> > > > > > >> >
> > >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> > >> > > > becket.qin@gmail.com>
> > >> > > > > > >> wrote:
> > >> > > > > > >> >
> > >> > > > > > >> > > Hi Jason,
> > >> > > > > > >> > >
> > >> > > > > > >> > > There are a few problems we want to solve here:
> > >> > > > > > >> > > 1. The group metadata is too big to be appended to
> the
> > >> log.
> > >> > > > > > >> > > 2. Reduce the memory footprint on the broker
> > >> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> > >> > > > > > >> > >
> > >> > > > > > >> > > To solve (1), I like your idea of having separate
> > >> messages
> > >> > per
> > >> > > > > > member.
> > >> > > > > > >> > The
> > >> > > > > > >> > > proposal (Onur's option 8) is to break metadata into
> > >> small
> > >> > > > records
> > >> > > > > > in
> > >> > > > > > >> the
> > >> > > > > > >> > > same uncompressed message set so each record is
> small.
> > I
> > >> > agree
> > >> > > > it
> > >> > > > > > >> would
> > >> > > > > > >> > be
> > >> > > > > > >> > > ideal if we are able to store the metadata separately
> > for
> > >> > each
> > >> > > > > > >> member. I
> > >> > > > > > >> > > was also thinking about storing the metadata into
> > >> multiple
> > >> > > > > messages,
> > >> > > > > > >> too.
> > >> > > > > > >> > > What concerns me was that having multiple messages
> > seems
> > >> > > > breaking
> > >> > > > > > the
> > >> > > > > > >> > > atomicity. I am not sure how we are going to deal
> with
> > >> the
> > >> > > > > potential
> > >> > > > > > >> > > issues. For example, What if group metadata is
> > replicated
> > >> > but
> > >> > > > the
> > >> > > > > > >> member
> > >> > > > > > >> > > metadata is not? It might be fine depending on the
> > >> > > > implementation
> > >> > > > > > >> though,
> > >> > > > > > >> > > but I am not sure.
> > >> > > > > > >> > >
> > >> > > > > > >> > > For (2) we want to store the metadata onto the disk,
> > >> which
> > >> > is
> > >> > > > what
> > >> > > > > > we
> > >> > > > > > >> > have
> > >> > > > > > >> > > to do anyway. The only question is in what format
> > should
> > >> we
> > >> > > > store
> > >> > > > > > >> them.
> > >> > > > > > >> > >
> > >> > > > > > >> > > To address (3) we want to have the metadata to be
> > >> > compressed,
> > >> > > > > which
> > >> > > > > > is
> > >> > > > > > >> > > contradict to the the above solution of (1).
> > >> > > > > > >> > >
> > >> > > > > > >> > > I think Jun's suggestion is probably still the
> > simplest.
> > >> To
> > >> > > > avoid
> > >> > > > > > >> > changing
> > >> > > > > > >> > > the behavior for consumers, maybe we can do that only
> > for
> > >> > > > > > >> offset_topic,
> > >> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is
> > >> smaller
> > >> > > than
> > >> > > > > the
> > >> > > > > > >> > > message size on the offset topic, we always return at
> > >> least
> > >> > > one
> > >> > > > > full
> > >> > > > > > >> > > message. This should avoid the unexpected problem on
> > the
> > >> > > client
> > >> > > > > side
> > >> > > > > > >> > > because supposedly only tools and brokers will fetch
> > from
> > >> > the
> > >> > > > the
> > >> > > > > > >> > internal
> > >> > > > > > >> > > topics,
> > >> > > > > > >> > >
> > >> > > > > > >> > > As a modification to what you suggested, one
> solution I
> > >> was
> > >> > > > > thinking
> > >> > > > > > >> was
> > >> > > > > > >> > to
> > >> > > > > > >> > > have multiple messages in a single compressed
> message.
> > >> That
> > >> > > > means
> > >> > > > > > for
> > >> > > > > > >> > > SyncGroupResponse we still need to read the entire
> > >> > compressed
> > >> > > > > > messages
> > >> > > > > > >> > and
> > >> > > > > > >> > > extract the inner messages, which seems not quite
> > >> different
> > >> > > from
> > >> > > > > > >> having a
> > >> > > > > > >> > > single message containing everything. But let me just
> > >> put it
> > >> > > > here
> > >> > > > > > and
> > >> > > > > > >> see
> > >> > > > > > >> > > if that makes sense.
> > >> > > > > > >> > >
> > >> > > > > > >> > > We can have a map of GroupMetadataKey ->
> > >> > > > GroupMetadataValueOffset.
> > >> > > > > > >> > >
> > >> > > > > > >> > > The GroupMetadataValue is stored in a compressed
> > message.
> > >> > The
> > >> > > > > inner
> > >> > > > > > >> > > messages are the following:
> > >> > > > > > >> > >
> > >> > > > > > >> > > Inner Message 0: Version GroupId Generation
> > >> > > > > > >> > >
> > >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can
> > >> compress
> > >> > > the
> > >> > > > > > bytes
> > >> > > > > > >> > here)
> > >> > > > > > >> > >
> > >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> > >> > > > > > >> > > ....
> > >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> > >> > > > > > >> > >
> > >> > > > > > >> > > The MemberMetadata format is the following:
> > >> > > > > > >> > >   MemberMetadata => Version Generation ClientId Host
> > >> > > > Subscription
> > >> > > > > > >> > > Assignment
> > >> > > > > > >> > >
> > >> > > > > > >> > > So DescribeGroupResponse will just return the entire
> > >> > > compressed
> > >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return
> the
> > >> > > > > > corresponding
> > >> > > > > > >> > inner
> > >> > > > > > >> > > message.
> > >> > > > > > >> > >
> > >> > > > > > >> > > Thanks,
> > >> > > > > > >> > >
> > >> > > > > > >> > > Jiangjie (Becket) Qin
> > >> > > > > > >> > >
> > >> > > > > > >> > >
> > >> > > > > > >> > >
> > >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson <
> > >> > > > > > jason@confluent.io>
> > >> > > > > > >> > > wrote:
> > >> > > > > > >> > >
> > >> > > > > > >> > > > Hey Becket,
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > I like your idea to store only the offset for the
> > group
> > >> > > > metadata
> > >> > > > > > in
> > >> > > > > > >> > > memory.
> > >> > > > > > >> > > > I think it would be safe to keep it in memory for a
> > >> short
> > >> > > time
> > >> > > > > > after
> > >> > > > > > >> > the
> > >> > > > > > >> > > > rebalance completes, but after that, it's only real
> > >> > purpose
> > >> > > is
> > >> > > > > to
> > >> > > > > > >> > answer
> > >> > > > > > >> > > > DescribeGroup requests, so your proposal makes a
> lot
> > of
> > >> > > sense
> > >> > > > to
> > >> > > > > > me.
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > As for the specific problem with the size of the
> > group
> > >> > > > metadata
> > >> > > > > > >> message
> > >> > > > > > >> > > for
> > >> > > > > > >> > > > the MM case, if we cannot succeed in reducing the
> > size
> > >> of
> > >> > > the
> > >> > > > > > >> > > > subscription/assignment (which I think is still
> > >> probably
> > >> > the
> > >> > > > > best
> > >> > > > > > >> > > > alternative if it can work), then I think there are
> > >> some
> > >> > > > options
> > >> > > > > > for
> > >> > > > > > >> > > > changing the message format (option #8 in Onur's
> > >> initial
> > >> > > > > e-mail).
> > >> > > > > > >> > > > Currently, the key used for storing the group
> > metadata
> > >> is
> > >> > > > this:
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > GroupMetadataKey => Version GroupId
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > And the value is something like this (some details
> > >> > elided):
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation
> > >> > > > > [MemberMetadata]
> > >> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
> > >> Assignment
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > I don't think we can change the key without a lot
> of
> > >> pain,
> > >> > > but
> > >> > > > > it
> > >> > > > > > >> seems
> > >> > > > > > >> > > > like we can change the value format. Maybe we can
> > take
> > >> the
> > >> > > > > > >> > > > subscription/assignment payloads out of the value
> and
> > >> > > > introduce
> > >> > > > > a
> > >> > > > > > >> new
> > >> > > > > > >> > > > "MemberMetadata" message for each member in the
> > group.
> > >> For
> > >> > > > > > example:
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > MemberMetadataValue => Version Generation ClientId
> > Host
> > >> > > > > > Subscription
> > >> > > > > > >> > > > Assignment
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > When a new generation is created, we would first
> > write
> > >> the
> > >> > > > group
> > >> > > > > > >> > metadata
> > >> > > > > > >> > > > message which includes the generation and all of
> the
> > >> > > > memberIds,
> > >> > > > > > and
> > >> > > > > > >> > then
> > >> > > > > > >> > > > we'd write the member metadata messages. To answer
> > the
> > >> > > > > > DescribeGroup
> > >> > > > > > >> > > > request, we'd read the group metadata at the cached
> > >> offset
> > >> > > > and,
> > >> > > > > > >> > depending
> > >> > > > > > >> > > > on the version, all of the following member
> metadata.
> > >> This
> > >> > > > would
> > >> > > > > > be
> > >> > > > > > >> > more
> > >> > > > > > >> > > > complex to maintain, but it seems doable if it
> comes
> > to
> > >> > it.
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > Thanks,
> > >> > > > > > >> > > > Jason
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> > >> > > > > becket.qin@gmail.com
> > >> > > > > > >
> > >> > > > > > >> > > wrote:
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > > It might worth thinking a little further. We have
> > >> > > discussed
> > >> > > > > this
> > >> > > > > > >> > before
> > >> > > > > > >> > > > > that we want to avoid holding all the group
> > metadata
> > >> in
> > >> > > > > memory.
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > I am thinking about the following end state:
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > 1. Enable compression on the offset topic.
> > >> > > > > > >> > > > > 2. Instead of holding the entire group metadata
> in
> > >> > memory
> > >> > > on
> > >> > > > > the
> > >> > > > > > >> > > brokers,
> > >> > > > > > >> > > > > each broker only keeps a [group -> Offset] map,
> the
> > >> > offset
> > >> > > > > > points
> > >> > > > > > >> to
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > message in the offset topic which holds the
> latest
> > >> > > metadata
> > >> > > > of
> > >> > > > > > the
> > >> > > > > > >> > > group.
> > >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the
> offset
> > >> topic
> > >> > > > > > directly
> > >> > > > > > >> > like
> > >> > > > > > >> > > a
> > >> > > > > > >> > > > > normal consumption, except that only exactly one
> > >> message
> > >> > > > will
> > >> > > > > be
> > >> > > > > > >> > > > returned.
> > >> > > > > > >> > > > > 4. SyncGroupResponse will read the message,
> extract
> > >> the
> > >> > > > > > assignment
> > >> > > > > > >> > part
> > >> > > > > > >> > > > and
> > >> > > > > > >> > > > > send back the partition assignment. We can
> compress
> > >> the
> > >> > > > > > partition
> > >> > > > > > >> > > > > assignment before sends it out if we want.
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > Jiangjie (Becket) Qin
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason Gustafson
> <
> > >> > > > > > >> jason@confluent.io
> > >> > > > > > >> > >
> > >> > > > > > >> > > > > wrote:
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression)
> > >> basically
> > >> > > do
> > >> > > > > > this?
> > >> > > > > > >> If
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > > topic
> > >> > > > > > >> > > > > > > is a string and the topic is repeated
> > throughout,
> > >> > > won't
> > >> > > > > > >> > compression
> > >> > > > > > >> > > > > > > basically replace all repeated instances of
> it
> > >> with
> > >> > an
> > >> > > > > index
> > >> > > > > > >> > > > reference
> > >> > > > > > >> > > > > to
> > >> > > > > > >> > > > > > > the full string?
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > > Hey James, yeah, that's probably true, but keep
> > in
> > >> > mind
> > >> > > > that
> > >> > > > > > the
> > >> > > > > > >> > > > > > compression happens on the broker side. It
> would
> > be
> > >> > nice
> > >> > > > to
> > >> > > > > > >> have a
> > >> > > > > > >> > > more
> > >> > > > > > >> > > > > > compact representation so that get some benefit
> > >> over
> > >> > the
> > >> > > > > wire
> > >> > > > > > as
> > >> > > > > > >> > > well.
> > >> > > > > > >> > > > > This
> > >> > > > > > >> > > > > > seems to be less of a concern here, so the
> bigger
> > >> > gains
> > >> > > > are
> > >> > > > > > >> > probably
> > >> > > > > > >> > > > from
> > >> > > > > > >> > > > > > reducing the number of partitions that need to
> be
> > >> > listed
> > >> > > > > > >> > > individually.
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > > -Jason
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur Karaman <
> > >> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> > >> > > > > > >> > > > > > wrote:
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > > > When figuring out these optimizations, it's
> > worth
> > >> > > > keeping
> > >> > > > > in
> > >> > > > > > >> mind
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > > > improvements when the message is uncompressed
> > vs
> > >> > when
> > >> > > > it's
> > >> > > > > > >> > > > compressed.
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > When uncompressed:
> > >> > > > > > >> > > > > > > Fixing the Assignment serialization to
> instead
> > >> be a
> > >> > > > topic
> > >> > > > > > >> index
> > >> > > > > > >> > > into
> > >> > > > > > >> > > > > the
> > >> > > > > > >> > > > > > > corresponding member's subscription list
> would
> > >> > usually
> > >> > > > be
> > >> > > > > a
> > >> > > > > > >> good
> > >> > > > > > >> > > > thing.
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > I think the proposal is only worse when the
> > topic
> > >> > > names
> > >> > > > > are
> > >> > > > > > >> > small.
> > >> > > > > > >> > > > The
> > >> > > > > > >> > > > > > > Type.STRING we use in our protocol for the
> > >> > > assignment's
> > >> > > > > > >> > > > TOPIC_KEY_NAME
> > >> > > > > > >> > > > > is
> > >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so our
> > >> strings
> > >> > > are
> > >> > > > > > first
> > >> > > > > > >> > > > > prepended
> > >> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > The new proposal does worse when:
> > >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> > >> > index_type_size
> > >> > > > > > >> > > > > > > in other words when:
> > >> > > > > > >> > > > > > > utf_encoded_string_payload_size <
> > >> index_type_size -
> > >> > 2
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > If the index type ends up being Type.INT32,
> > then
> > >> the
> > >> > > > > > proposal
> > >> > > > > > >> is
> > >> > > > > > >> > > > worse
> > >> > > > > > >> > > > > > when
> > >> > > > > > >> > > > > > > the topic is length 1.
> > >> > > > > > >> > > > > > > If the index type ends up being Type.INT64,
> > then
> > >> the
> > >> > > > > > proposal
> > >> > > > > > >> is
> > >> > > > > > >> > > > worse
> > >> > > > > > >> > > > > > when
> > >> > > > > > >> > > > > > > the topic is less than length 6.
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > When compressed:
> > >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how
> > >> things
> > >> > > > change
> > >> > > > > > when
> > >> > > > > > >> > > > > > compression
> > >> > > > > > >> > > > > > > comes into the picture. This would be worth
> > >> > > > investigating.
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James Cheng
> <
> > >> > > > > > >> > wushujames@gmail.com
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > > > wrote:
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
> > >> Gustafson <
> > >> > > > > > >> > > > jason@confluent.io>
> > >> > > > > > >> > > > > > > > wrote:
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay out
> > the
> > >> > > > > assignment
> > >> > > > > > >> > without
> > >> > > > > > >> > > > > > needing
> > >> > > > > > >> > > > > > > > to
> > >> > > > > > >> > > > > > > > > explicitly repeat the topic? For example,
> > the
> > >> > > leader
> > >> > > > > > could
> > >> > > > > > >> > sort
> > >> > > > > > >> > > > the
> > >> > > > > > >> > > > > > > > topics
> > >> > > > > > >> > > > > > > > > for each member and just use an integer
> to
> > >> > > represent
> > >> > > > > the
> > >> > > > > > >> > index
> > >> > > > > > >> > > of
> > >> > > > > > >> > > > > > each
> > >> > > > > > >> > > > > > > > > topic within the sorted list (note this
> > >> depends
> > >> > on
> > >> > > > the
> > >> > > > > > >> > > > subscription
> > >> > > > > > >> > > > > > > > > including the full topic list).
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]]
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other compression)
> > >> > basically
> > >> > > > do
> > >> > > > > > >> this?
> > >> > > > > > >> > If
> > >> > > > > > >> > > > the
> > >> > > > > > >> > > > > > > topic
> > >> > > > > > >> > > > > > > > is a string and the topic is repeated
> > >> throughout,
> > >> > > > won't
> > >> > > > > > >> > > compression
> > >> > > > > > >> > > > > > > > basically replace all repeated instances of
> > it
> > >> > with
> > >> > > an
> > >> > > > > > index
> > >> > > > > > >> > > > > reference
> > >> > > > > > >> > > > > > to
> > >> > > > > > >> > > > > > > > the full string?
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > > > -James
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > > > > You could even combine these two options
> so
> > >> that
> > >> > > you
> > >> > > > > > have
> > >> > > > > > >> > only
> > >> > > > > > >> > > 3
> > >> > > > > > >> > > > > > > integers
> > >> > > > > > >> > > > > > > > > for each topic assignment:
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition
> > >> > > MaxPartition]
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > There may even be better options with a
> > >> little
> > >> > > more
> > >> > > > > > >> thought.
> > >> > > > > > >> > > All
> > >> > > > > > >> > > > of
> > >> > > > > > >> > > > > > > this
> > >> > > > > > >> > > > > > > > is
> > >> > > > > > >> > > > > > > > > just part of the client-side protocol, so
> > it
> > >> > > > wouldn't
> > >> > > > > > >> require
> > >> > > > > > >> > > any
> > >> > > > > > >> > > > > > > version
> > >> > > > > > >> > > > > > > > > bumps on the broker. What do you think?
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > Thanks,
> > >> > > > > > >> > > > > > > > > Jason
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM, Guozhang
> > >> Wang <
> > >> > > > > > >> > > > wangguoz@gmail.com
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > > > > > wrote:
> > >> > > > > > >> > > > > > > > >
> > >> > > > > > >> > > > > > > > >> The original concern is that regex may
> not
> > >> be
> > >> > > > > > efficiently
> > >> > > > > > >> > > > > supported
> > >> > > > > > >> > > > > > > > >> across-languages, but if there is a neat
> > >> > > > workaround I
> > >> > > > > > >> would
> > >> > > > > > >> > > love
> > >> > > > > > >> > > > > to
> > >> > > > > > >> > > > > > > > learn.
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >> Guozhang
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM, Ismael
> > >> Juma <
> > >> > > > > > >> > > ismael@juma.me.uk
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > > > > > wrote:
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>> Having said that, as a general point, I
> > >> think
> > >> > we
> > >> > > > > > should
> > >> > > > > > >> > > > consider
> > >> > > > > > >> > > > > > > > >> supporting
> > >> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol. It
> > >> > requires
> > >> > > > > some
> > >> > > > > > >> > > thinking
> > >> > > > > > >> > > > > for
> > >> > > > > > >> > > > > > > > >>> cross-language support, but it seems
> > >> > > surmountable
> > >> > > > > and
> > >> > > > > > it
> > >> > > > > > >> > > could
> > >> > > > > > >> > > > > make
> > >> > > > > > >> > > > > > > > >> certain
> > >> > > > > > >> > > > > > > > >>> operations a lot more efficient (the
> fact
> > >> > that a
> > >> > > > > basic
> > >> > > > > > >> > regex
> > >> > > > > > >> > > > > > > > subscription
> > >> > > > > > >> > > > > > > > >>> causes the consumer to request metadata
> > for
> > >> > all
> > >> > > > > topics
> > >> > > > > > >> is
> > >> > > > > > >> > not
> > >> > > > > > >> > > > > > great).
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>> Ismael
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM,
> > Guozhang
> > >> > Wang
> > >> > > <
> > >> > > > > > >> > > > > > wangguoz@gmail.com>
> > >> > > > > > >> > > > > > > > >>> wrote:
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing
> the
> > >> > > handling
> > >> > > > > > >> logics of
> > >> > > > > > >> > > > > single
> > >> > > > > > >> > > > > > > > large
> > >> > > > > > >> > > > > > > > >>>> message on the consumer side.
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>> As for the case of "a single group
> > >> > subscribing
> > >> > > to
> > >> > > > > > 3000
> > >> > > > > > >> > > > topics",
> > >> > > > > > >> > > > > > with
> > >> > > > > > >> > > > > > > > >> 100
> > >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
> > >> reasonable
> > >> > to
> > >> > > me
> > >> > > > > > (when
> > >> > > > > > >> > > > storing
> > >> > > > > > >> > > > > in
> > >> > > > > > >> > > > > > > ZK,
> > >> > > > > > >> > > > > > > > >> we
> > >> > > > > > >> > > > > > > > >>>> also have the znode limit which is set
> > to
> > >> 1Mb
> > >> > > by
> > >> > > > > > >> default,
> > >> > > > > > >> > > > though
> > >> > > > > > >> > > > > > > > >>> admittedly
> > >> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if
> we
> > do
> > >> > the
> > >> > > > > change
> > >> > > > > > >> as
> > >> > > > > > >> > Jun
> > >> > > > > > >> > > > > > > > suggested,
> > >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure is
> > OK
> > >> I
> > >> > > > think.
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>> Guozhang
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM, Onur
> > >> > Karaman
> > >> > > <
> > >> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> > >> > > > > > >> > > > > > > > >>>>> wrote:
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>>> Results without compression:
> > >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> > >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the
> tipping
> > >> > point
> > >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> > >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> > >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> > >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> > >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> > >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> > >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> > >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> > >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> > >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> > >> > > > > > >> > > > > > > > >>>>>
> > >> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression
> > shrinks
> > >> > the
> > >> > > > > > message
> > >> > > > > > >> > size
> > >> > > > > > >> > > by
> > >> > > > > > >> > > > > 4x.
> > >> > > > > > >> > > > > > > > >>>>>
> > >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM, Jun
> > Rao
> > >> <
> > >> > > > > > >> > jun@confluent.io
> > >> > > > > > >> > > >
> > >> > > > > > >> > > > > > wrote:
> > >> > > > > > >> > > > > > > > >>>>>
> > >> > > > > > >> > > > > > > > >>>>>> Onur,
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how we
> > >> deal
> > >> > > with
> > >> > > > > the
> > >> > > > > > >> case
> > >> > > > > > >> > > > when a
> > >> > > > > > >> > > > > > > > >>> message
> > >> > > > > > >> > > > > > > > >>>> is
> > >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today,
> if
> > >> the
> > >> > > fetch
> > >> > > > > > size
> > >> > > > > > >> is
> > >> > > > > > >> > > > > smaller
> > >> > > > > > >> > > > > > > > >> than
> > >> > > > > > >> > > > > > > > >>>> the
> > >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get
> > stuck.
> > >> > > > Instead,
> > >> > > > > > we
> > >> > > > > > >> can
> > >> > > > > > >> > > > > simply
> > >> > > > > > >> > > > > > > > >>> return
> > >> > > > > > >> > > > > > > > >>>>> the
> > >> > > > > > >> > > > > > > > >>>>>> full message if it's larger than the
> > >> fetch
> > >> > > size
> > >> > > > > w/o
> > >> > > > > > >> > > > requiring
> > >> > > > > > >> > > > > > the
> > >> > > > > > >> > > > > > > > >>>>> consumer
> > >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size.
> On
> > >> the
> > >> > > > broker
> > >> > > > > > >> side,
> > >> > > > > > >> > to
> > >> > > > > > >> > > > > serve
> > >> > > > > > >> > > > > > a
> > >> > > > > > >> > > > > > > > >>> fetch
> > >> > > > > > >> > > > > > > > >>>>>> request, we already do an index
> lookup
> > >> and
> > >> > > then
> > >> > > > > > scan
> > >> > > > > > >> the
> > >> > > > > > >> > > > log a
> > >> > > > > > >> > > > > > bit
> > >> > > > > > >> > > > > > > > >> to
> > >> > > > > > >> > > > > > > > >>>>> find
> > >> > > > > > >> > > > > > > > >>>>>> the message with the requested
> offset.
> > >> We
> > >> > can
> > >> > > > > just
> > >> > > > > > >> check
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > > size
> > >> > > > > > >> > > > > > > > >> of
> > >> > > > > > >> > > > > > > > >>>> that
> > >> > > > > > >> > > > > > > > >>>>>> message and return the full message
> if
> > >> its
> > >> > > size
> > >> > > > > is
> > >> > > > > > >> > larger
> > >> > > > > > >> > > > than
> > >> > > > > > >> > > > > > the
> > >> > > > > > >> > > > > > > > >>>> fetch
> > >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is really
> > for
> > >> > > > > > performance
> > >> > > > > > >> > > > > > optimization,
> > >> > > > > > >> > > > > > > > >>> i.e.
> > >> > > > > > >> > > > > > > > >>>>> in
> > >> > > > > > >> > > > > > > > >>>>>> the common case, we will not return
> > more
> > >> > > bytes
> > >> > > > > than
> > >> > > > > > >> > fetch
> > >> > > > > > >> > > > > size,
> > >> > > > > > >> > > > > > > but
> > >> > > > > > >> > > > > > > > >>> if
> > >> > > > > > >> > > > > > > > >>>>>> there is a large message, we will
> > return
> > >> > more
> > >> > > > > bytes
> > >> > > > > > >> than
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > > > > >>> specified
> > >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large
> > messages
> > >> are
> > >> > > > rare.
> > >> > > > > > >> So, it
> > >> > > > > > >> > > > > > shouldn't
> > >> > > > > > >> > > > > > > > >>>>> increase
> > >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the client
> > too
> > >> > > much.
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>> Jun
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM,
> Onur
> > >> > > Karaman <
> > >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> > >> > > > > > >> > > > > > > > >>>>>> wrote:
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing
> some
> > >> > tests
> > >> > > on
> > >> > > > > the
> > >> > > > > > >> new
> > >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> > >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more
> > >> strenuous
> > >> > use
> > >> > > > > cases
> > >> > > > > > >> like
> > >> > > > > > >> > > > > > mirroring
> > >> > > > > > >> > > > > > > > >>>>>> clusters
> > >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and
> thought
> > >> I'd
> > >> > > share
> > >> > > > > > >> > whatever I
> > >> > > > > > >> > > > > have
> > >> > > > > > >> > > > > > so
> > >> > > > > > >> > > > > > > > >>>> far.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount
> of
> > >> group
> > >> > > > > > metadata
> > >> > > > > > >> we
> > >> > > > > > >> > > can
> > >> > > > > > >> > > > > fit
> > >> > > > > > >> > > > > > > > >> into
> > >> > > > > > >> > > > > > > > >>>> one
> > >> > > > > > >> > > > > > > > >>>>>>> message
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Some background:
> > >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is
> implemented
> > >> in
> > >> > two
> > >> > > > > > phases
> > >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase that
> > >> > > identifies
> > >> > > > > > >> members
> > >> > > > > > >> > of
> > >> > > > > > >> > > > the
> > >> > > > > > >> > > > > > > > >> group
> > >> > > > > > >> > > > > > > > >>>> and
> > >> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions.
> > >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that waits
> > for
> > >> > the
> > >> > > > > group
> > >> > > > > > >> > leader
> > >> > > > > > >> > > to
> > >> > > > > > >> > > > > > > > >> decide
> > >> > > > > > >> > > > > > > > >>>>> member
> > >> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
> > >> > > subscriptions
> > >> > > > > > across
> > >> > > > > > >> > the
> > >> > > > > > >> > > > > group.
> > >> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this
> decision
> > >> > with a
> > >> > > > > > >> > > > > SyncGroupRequest.
> > >> > > > > > >> > > > > > > > >> The
> > >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> > >> SyncGroupRequests
> > >> > > by
> > >> > > > > > >> appending
> > >> > > > > > >> > > all
> > >> > > > > > >> > > > > > group
> > >> > > > > > >> > > > > > > > >>>> state
> > >> > > > > > >> > > > > > > > >>>>>>> into a single message under the
> > >> > > > > __consumer_offsets
> > >> > > > > > >> > topic.
> > >> > > > > > >> > > > > This
> > >> > > > > > >> > > > > > > > >>>> message
> > >> > > > > > >> > > > > > > > >>>>> is
> > >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and contains
> > each
> > >> > > member
> > >> > > > > > >> > > subscription
> > >> > > > > > >> > > > > as
> > >> > > > > > >> > > > > > > > >> well
> > >> > > > > > >> > > > > > > > >>>> as
> > >> > > > > > >> > > > > > > > >>>>>> the
> > >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each member.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> The environment:
> > >> > > > > > >> > > > > > > > >>>>>>> - one broker
> > >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets partition
> > >> > > > > > >> > > > > > > > >>>>>>> - offsets.topic.compression.codec=1
> > //
> > >> > this
> > >> > > is
> > >> > > > > > gzip
> > >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending KAFKA-3718
> > >> patch
> > >> > > that
> > >> > > > > > >> actually
> > >> > > > > > >> > > > makes
> > >> > > > > > >> > > > > > use
> > >> > > > > > >> > > > > > > > >> of
> > >> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec:
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> https://github.com/apache/kafka/pull/1394
> > >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an
> > actual
> > >> > > subset
> > >> > > > > of
> > >> > > > > > >> > topics
> > >> > > > > > >> > > > from
> > >> > > > > > >> > > > > > one
> > >> > > > > > >> > > > > > > > >>> of
> > >> > > > > > >> > > > > > > > >>>>> our
> > >> > > > > > >> > > > > > > > >>>>>>> clusters.
> > >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> > >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long on
> > >> average
> > >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number
> of
> > >> > > consumers
> > >> > > > > > each
> > >> > > > > > >> > > > hardcoded
> > >> > > > > > >> > > > > > > > >> with
> > >> > > > > > >> > > > > > > > >>>> all
> > >> > > > > > >> > > > > > > > >>>>>> the
> > >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests more
> > >> > > consistent.
> > >> > > > > > >> > > wildcarding
> > >> > > > > > >> > > > > with
> > >> > > > > > >> > > > > > > > >> .*
> > >> > > > > > >> > > > > > > > >>>>> should
> > >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> > >> subscription
> > >> > > > hits
> > >> > > > > > the
> > >> > > > > > >> > > > > coordinator
> > >> > > > > > >> > > > > > > > >> as
> > >> > > > > > >> > > > > > > > >>>> the
> > >> > > > > > >> > > > > > > > >>>>>>> subscription has already been fully
> > >> > expanded
> > >> > > > out
> > >> > > > > > to
> > >> > > > > > >> the
> > >> > > > > > >> > > > list
> > >> > > > > > >> > > > > of
> > >> > > > > > >> > > > > > > > >>>> topics
> > >> > > > > > >> > > > > > > > >>>>> by
> > >> > > > > > >> > > > > > > > >>>>>>> the consumers.
> > >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to
> > >> Log.scala
> > >> > to
> > >> > > > > print
> > >> > > > > > >> out
> > >> > > > > > >> > the
> > >> > > > > > >> > > > > > message
> > >> > > > > > >> > > > > > > > >>>> sizes
> > >> > > > > > >> > > > > > > > >>>>>>> after compression
> > >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all and
> > >> auto
> > >> > > > commits
> > >> > > > > > are
> > >> > > > > > >> > > > > disabled.
> > >> > > > > > >> > > > > > > > >> The
> > >> > > > > > >> > > > > > > > >>>> only
> > >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added
> is
> > >> the
> > >> > > > > > >> > > __consumer_offsets
> > >> > > > > > >> > > > > > topic
> > >> > > > > > >> > > > > > > > >>> and
> > >> > > > > > >> > > > > > > > >>>>>>> they're only from storing group
> > >> metadata
> > >> > > while
> > >> > > > > > >> > processing
> > >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Results:
> > >> > > > > > >> > > > > > > > >>>>>>> The results below show that we
> exceed
> > >> the
> > >> > > > > 1000012
> > >> > > > > > >> byte
> > >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit
> > >> > relatively
> > >> > > > > > quickly
> > >> > > > > > >> > > > (between
> > >> > > > > > >> > > > > > > > >> 30-40
> > >> > > > > > >> > > > > > > > >>>>>>> consumers):
> > >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the
> > >> tipping
> > >> > > point
> > >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> > >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is
> pretty
> > >> > > gradual.
> > >> > > > > > >> Plotting
> > >> > > > > > >> > > the
> > >> > > > > > >> > > > > > > > >> points
> > >> > > > > > >> > > > > > > > >>>>> makes
> > >> > > > > > >> > > > > > > > >>>>>> it
> > >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the
> number
> > of
> > >> > > > > consumers:
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > >
> > >> > > > > > >> > >
> > >> > > > > > >> >
> > >> > > > > > >>
> > >> > > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> >
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers aren't
> > >> > averages
> > >> > > > or
> > >> > > > > > >> medians
> > >> > > > > > >> > > or
> > >> > > > > > >> > > > > > > > >> anything
> > >> > > > > > >> > > > > > > > >>>>> like
> > >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size from
> a
> > >> given
> > >> > > > run.
> > >> > > > > I
> > >> > > > > > >> did
> > >> > > > > > >> > run
> > >> > > > > > >> > > > > them
> > >> > > > > > >> > > > > > a
> > >> > > > > > >> > > > > > > > >>> few
> > >> > > > > > >> > > > > > > > >>>>>> times
> > >> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Impact:
> > >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> > >> > > > __consumer_offsets
> > >> > > > > > >> topic
> > >> > > > > > >> > > with
> > >> > > > > > >> > > > > my
> > >> > > > > > >> > > > > > > > >>>> pending
> > >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the AwaitingSync
> > >> phase
> > >> > of
> > >> > > > the
> > >> > > > > > >> group
> > >> > > > > > >> > > fails
> > >> > > > > > >> > > > > > with
> > >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This means
> > the
> > >> > > > combined
> > >> > > > > > >> size
> > >> > > > > > >> > of
> > >> > > > > > >> > > > each
> > >> > > > > > >> > > > > > > > >>>> member's
> > >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments
> > exceeded
> > >> the
> > >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> > >> > > > > > >> > > > > > > > >>>>> of
> > >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up
> > dying.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Options:
> > >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the number
> > of
> > >> > > > consumers
> > >> > > > > > in
> > >> > > > > > >> the
> > >> > > > > > >> > > > > group.
> > >> > > > > > >> > > > > > > > >> This
> > >> > > > > > >> > > > > > > > >>>>> isn't
> > >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more
> > >> > strenuous
> > >> > > > use
> > >> > > > > > >> cases
> > >> > > > > > >> > > like
> > >> > > > > > >> > > > > > > > >>>> MirrorMaker
> > >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> > >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group
> > into
> > >> > > smaller
> > >> > > > > > >> groups
> > >> > > > > > >> > > which
> > >> > > > > > >> > > > > > > > >>> together
> > >> > > > > > >> > > > > > > > >>>>> will
> > >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics.
> This
> > >> > gives
> > >> > > > each
> > >> > > > > > >> group
> > >> > > > > > >> > > > > member a
> > >> > > > > > >> > > > > > > > >>>> smaller
> > >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics
> > >> starting
> > >> > > with
> > >> > > > > a-m
> > >> > > > > > >> while
> > >> > > > > > >> > > g2
> > >> > > > > > >> > > > > has
> > >> > > > > > >> > > > > > > > >>> topics
> > >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be
> > >> > > operationally
> > >> > > > > > >> painful
> > >> > > > > > >> > to
> > >> > > > > > >> > > > > > manage.
> > >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the topics
> > >> among
> > >> > > > members
> > >> > > > > > of
> > >> > > > > > >> the
> > >> > > > > > >> > > > > group.
> > >> > > > > > >> > > > > > > > >>> Again
> > >> > > > > > >> > > > > > > > >>>>> this
> > >> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller
> > >> > > > subscription.
> > >> > > > > > This
> > >> > > > > > >> > > would
> > >> > > > > > >> > > > > also
> > >> > > > > > >> > > > > > > > >> be
> > >> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage.
> > >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> > >> > > > > > >> KafkaConfig.messageMaxBytes
> > >> > > > > > >> > (a
> > >> > > > > > >> > > > > > > > >>> topic-level
> > >> > > > > > >> > > > > > > > >>>>>>> config) and
> > >> > KafkaConfig.replicaFetchMaxBytes
> > >> > > > (a
> > >> > > > > > >> > > > broker-level
> > >> > > > > > >> > > > > > > > >>> config).
> > >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just
> the
> > >> > > > > > >> __consumer_offsets
> > >> > > > > > >> > > > topic
> > >> > > > > > >> > > > > > > > >> seems
> > >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping up
> > the
> > >> > > > > > broker-level
> > >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> > >> > > > > > >> > > > > > > > >>>>>>> would probably need more attention.
> > >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
> > >> > compression
> > >> > > > > > codecs.
> > >> > > > > > >> > Based
> > >> > > > > > >> > > > on
> > >> > > > > > >> > > > > 2
> > >> > > > > > >> > > > > > > > >>>> minutes
> > >> > > > > > >> > > > > > > > >>>>> of
> > >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and
> > snappy
> > >> are
> > >> > > > > faster
> > >> > > > > > >> than
> > >> > > > > > >> > > gzip
> > >> > > > > > >> > > > > but
> > >> > > > > > >> > > > > > > > >>> have
> > >> > > > > > >> > > > > > > > >>>>>> worse
> > >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably won't
> > >> help.
> > >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support
> > >> sending
> > >> > > the
> > >> > > > > > regex
> > >> > > > > > >> > over
> > >> > > > > > >> > > > the
> > >> > > > > > >> > > > > > wire
> > >> > > > > > >> > > > > > > > >>>>> instead
> > >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> > >> > subscriptions. I
> > >> > > > > think
> > >> > > > > > >> > people
> > >> > > > > > >> > > > > said
> > >> > > > > > >> > > > > > in
> > >> > > > > > >> > > > > > > > >>> the
> > >> > > > > > >> > > > > > > > >>>>>> past
> > >> > > > > > >> > > > > > > > >>>>>>> that different languages have
> subtle
> > >> > > > differences
> > >> > > > > > in
> > >> > > > > > >> > > regex,
> > >> > > > > > >> > > > so
> > >> > > > > > >> > > > > > > > >> this
> > >> > > > > > >> > > > > > > > >>>>>> doesn't
> > >> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language
> > groups.
> > >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe we
> > can
> > >> > > reverse
> > >> > > > > the
> > >> > > > > > >> > > mapping?
> > >> > > > > > >> > > > > > > > >> Instead
> > >> > > > > > >> > > > > > > > >>>> of
> > >> > > > > > >> > > > > > > > >>>>>>> mapping from member to
> subscriptions,
> > >> we
> > >> > can
> > >> > > > > map a
> > >> > > > > > >> > > > > subscription
> > >> > > > > > >> > > > > > > > >> to
> > >> > > > > > >> > > > > > > > >>> a
> > >> > > > > > >> > > > > > > > >>>>> list
> > >> > > > > > >> > > > > > > > >>>>>>> of members.
> > >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe we
> > can
> > >> try
> > >> > > to
> > >> > > > > > break
> > >> > > > > > >> > apart
> > >> > > > > > >> > > > the
> > >> > > > > > >> > > > > > > > >>>>>> subscription
> > >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> > >> > > SyncGroupRequest
> > >> > > > > > into
> > >> > > > > > >> > > > multiple
> > >> > > > > > >> > > > > > > > >>> records?
> > >> > > > > > >> > > > > > > > >>>>>> They
> > >> > > > > > >> > > > > > > > >>>>>>> can still go to the same message
> set
> > >> and
> > >> > get
> > >> > > > > > >> appended
> > >> > > > > > >> > > > > together.
> > >> > > > > > >> > > > > > > > >>> This
> > >> > > > > > >> > > > > > > > >>>>> way
> > >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment size,
> > >> which
> > >> > > > > shouldn't
> > >> > > > > > >> be a
> > >> > > > > > >> > > > > > problem.
> > >> > > > > > >> > > > > > > > >>> This
> > >> > > > > > >> > > > > > > > >>>>> can
> > >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because
> we're
> > >> > > currently
> > >> > > > > > >> keying
> > >> > > > > > >> > > these
> > >> > > > > > >> > > > > > > > >>> messages
> > >> > > > > > >> > > > > > > > >>>> on
> > >> > > > > > >> > > > > > > > >>>>>> the
> > >> > > > > > >> > > > > > > > >>>>>>> group, so I think records from the
> > same
> > >> > > > > rebalance
> > >> > > > > > >> might
> > >> > > > > > >> > > > > > > > >>> accidentally
> > >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> > >> understanding
> > >> > of
> > >> > > > > > >> compaction
> > >> > > > > > >> > > > isn't
> > >> > > > > > >> > > > > > > > >> that
> > >> > > > > > >> > > > > > > > >>>>> great.
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> Todo:
> > >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun
> the
> > >> tests
> > >> > > > with
> > >> > > > > no
> > >> > > > > > >> > > > > compression
> > >> > > > > > >> > > > > > > > >> just
> > >> > > > > > >> > > > > > > > >>>> to
> > >> > > > > > >> > > > > > > > >>>>>> see
> > >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's
> > >> getting
> > >> > > > late.
> > >> > > > > > >> Maybe
> > >> > > > > > >> > > > > tomorrow?
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>> - Onur
> > >> > > > > > >> > > > > > > > >>>>>>>
> > >> > > > > > >> > > > > > > > >>>>>>
> > >> > > > > > >> > > > > > > > >>>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>> --
> > >> > > > > > >> > > > > > > > >>>> -- Guozhang
> > >> > > > > > >> > > > > > > > >>>>
> > >> > > > > > >> > > > > > > > >>>
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > > >> --
> > >> > > > > > >> > > > > > > > >> -- Guozhang
> > >> > > > > > >> > > > > > > > >>
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > > >
> > >> > > > > > >> > > > > > >
> > >> > > > > > >> > > > > >
> > >> > > > > > >> > > > >
> > >> > > > > > >> > > >
> > >> > > > > > >> > >
> > >> > > > > > >> >
> > >> > > > > > >> >
> > >> > > > > > >> >
> > >> > > > > > >> > --
> > >> > > > > > >> > -- Guozhang
> > >> > > > > > >> >
> > >> > > > > > >>
> > >> > > > > > >
> > >> > > > > > >
> > >> > > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> > >
> > >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Becket Qin <be...@gmail.com>]

I think taking bigger one of the fetch size and message size limit is
probably good enough. If we have a separate
"offset.replica.fetch.max.bytes", I guess the value will always be set to
max message size of the __consumer_offsets topic, which does not seem to
have much value.

On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman <ok...@linkedin.com.invalid>
wrote:

> Maybe another approach can be to add a new
> "offsets.replica.fetch.max.bytes" config on the brokers.
>
> On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <ok...@linkedin.com>
> wrote:
>
> > I made a PR with a tweak to Jun's/Becket's proposal:
> > https://github.com/apache/kafka/pull/1484
> >
> > It just tweaks the fetch behavior specifically for replicas fetching from
> > the __consumer_offsets topic when the fetcher's "replica.fetch.max.bytes"
> > is less than the __consumer_offset leader's "message.max.bytes" to take
> the
> > max of the two.
> >
> > I'm honestly not that happy with this solution, as I'd rather not change
> > the "replica.fetch.max.bytes" config from being a limit to a
> > recommendation. I'd definitely be happy to hear other alternatives!
> >
> > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> > onurkaraman.apache@gmail.com> wrote:
> >
> >> Sorry I know next to nothing about Kafka Connect. I didn't understand
> the
> >> Kafka Connect / MM idea you brought up. Can you go into more detail?
> >>
> >> Otherwise I think our remaining options are:
> >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
> >> __consumer_offsets topic and change the fetch behavior when message size
> >> is
> >> larger than fetch size
> >> - option 6: support sending the regex over the wire instead of the fully
> >> expanded topic subscriptions. This should cut down the message size from
> >> the subscription side. Again this only helps when pattern-based
> >> subscriptions are done.
> >>
> >> minor correction to an earlier comment I made regarding the message
> size:
> >> message size ~ sum(s_i + a_i for i in range [1, |C|])
> >>
> >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <ja...@confluent.io>
> >> wrote:
> >>
> >> > Hey Onur,
> >> >
> >> > Thanks for the investigation. It seems the conclusion is that the
> >> compact
> >> > format helps, but perhaps not enough to justify adding a new
> assignment
> >> > schema? I'm not sure there's much more room for savings unless we
> change
> >> > something more fundamental in the assignment approach. We spent some
> >> time
> >> > thinking before about whether we could let the consumers compute their
> >> > assignment locally from a smaller set of information, but the
> difficulty
> >> > (I'm sure you remember) is reaching consensus on topic metadata. Kafka
> >> > Connect has a similar problem where all the workers need to agree on
> >> > connector configurations. Since all configs are stored in a single
> topic
> >> > partition, the approach we take there is to propagate the offset in
> the
> >> > assignment protocol. Not sure if we could do something similar for
> MM...
> >> > Anyway, it seems like the best workaround at the moment is Jun's
> initial
> >> > suggestion. What do you think?
> >> >
> >> > -Jason
> >> >
> >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
> >> > onurkaraman.apache@gmail.com
> >> > > wrote:
> >> >
> >> > > I gave the topic index assignment trick a try against the same
> >> > environment.
> >> > > The implementation just changed the assignment serialization and
> >> > > deserialization logic. It didn't change SyncGroupResponse, meaning
> it
> >> > > continues to exclude the subscription from the SyncGroupResponse and
> >> > > assumes the member has kept track of its last subscription.
> >> > >
> >> > > Assignment topic indexing with compression:
> >> > > 1 consumer 34346 bytes
> >> > > 5 consumers 177687 bytes
> >> > > 10 consumers 331897 bytes
> >> > > 20 consumers 572467 bytes
> >> > > 30 consumers 811269 bytes
> >> > > 40 consumers 1047188 bytes * the tipping point
> >> > > 50 consumers 1290092 bytes
> >> > > 60 consumers 1527806 bytes
> >> > > 70 consumers 1769259 bytes
> >> > > 80 consumers 2000118 bytes
> >> > > 90 consumers 2244392 bytes
> >> > > 100 consumers 2482415 bytes
> >> > >
> >> > > Assignment topic indexing without compression:
> >> > > 1 consumer 211904 bytes
> >> > > 5 consumers 677184 bytes
> >> > > 10 consumers 1211154 bytes * the tipping point
> >> > > 20 consumers 2136196 bytes
> >> > > 30 consumers 3061238 bytes
> >> > > 40 consumers 3986280 bytes
> >> > > 50 consumers 4911322 bytes
> >> > > 60 consumers 5836284 bytes
> >> > > 70 consumers 6761246 bytes
> >> > > 80 consumers 7686208 bytes
> >> > > 90 consumers 8611170 bytes
> >> > > 100 consumers 9536132 bytes
> >> > >
> >> > > Assignment topic indexing seems to reduce the size by 500KB without
> >> > > compression and 80KB with compression. So assignment topic indexing
> >> makes
> >> > > some difference in both with and without compression but in our case
> >> was
> >> > > not nearly enough.
> >> > >
> >> > > This can be explained by the fact that we aren't actually hitting
> the
> >> > worst
> >> > > case scenario of each consumer being assigned a partition from every
> >> > topic.
> >> > > The reason is simple: a topic can only fully span all the consumers
> >> if it
> >> > > has at least as many partitions as there are consumers. Given that
> >> there
> >> > > are 8 partitions per topic and we have 100 consumers, it makes sense
> >> that
> >> > > we aren't close to this worse case scenario where topic indexing
> would
> >> > make
> >> > > a bigger difference.
> >> > >
> >> > > I tweaked the group leader's assignment code to print out the
> >> assignments
> >> > > and found that each consumer was getting either 238 or 239
> partitions.
> >> > Each
> >> > > of these partitions were from unique topics. So the consumers were
> >> really
> >> > > getting partitions from 239 topics instead of the full worst case
> >> > scenario
> >> > > of 3000 topics.
> >> > >
> >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <
> jason@confluent.io>
> >> > > wrote:
> >> > >
> >> > > > Gwen, Joel:
> >> > > >
> >> > > > That's correct. The protocol does allow us to give an assignor its
> >> own
> >> > > > assignment schema, but I think this will require a couple internal
> >> > > changes
> >> > > > to the consumer to make use of the full generality.
> >> > > >
> >> > > > One thing I'm a little uncertain about is whether we should use a
> >> > > different
> >> > > > protocol type. For a little context, the group membership protocol
> >> > allows
> >> > > > the client to provide a "protocol type" when joining the group to
> >> > ensure
> >> > > > that all members have some basic semantic compatibility. For
> >> example,
> >> > the
> >> > > > consumer uses "consumer" and Kafka Connect uses "connect."
> Currently
> >> > all
> >> > > > assignors using the "consumer" protocol share a common schema for
> >> > > > representing subscriptions and assignment. This is convenient for
> >> tools
> >> > > > (like consumer-groups.sh) since they just need to know how to
> parse
> >> the
> >> > > > "consumer" protocol type without knowing anything about the
> >> assignors.
> >> > So
> >> > > > introducing another schema would break that assumption and we'd
> need
> >> > > those
> >> > > > tools to do assignor-specific parsing. Maybe this is OK?
> >> Alternatively,
> >> > > we
> >> > > > could use a separate protocol type (e.g. "compact-consumer"), but
> >> that
> >> > > > seems less than desirable.
> >> > > >
> >> > > > Thanks,
> >> > > > Jason
> >> > > >
> >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <gwen@confluent.io
> >
> >> > > wrote:
> >> > > >
> >> > > > > ah, right - we can add as many strategies as we want.
> >> > > > >
> >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <
> jjkoshy.w@gmail.com
> >> >
> >> > > > wrote:
> >> > > > >
> >> > > > > > > Yes it would be a protocol bump.
> >> > > > > > >
> >> > > > > >
> >> > > > > > Sorry - I'm officially confused. I think it may not be
> required
> >> -
> >> > > since
> >> > > > > the
> >> > > > > > more compact format would be associated with a new assignment
> >> > > strategy
> >> > > > -
> >> > > > > > right?
> >> > > > > >
> >> > > > > >
> >> > > > > > > smaller than the plaintext PAL, but the post-compressed
> binary
> >> > PAL
> >> > > is
> >> > > > > > just
> >> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW
> using
> >> a
> >> > > > symbol
> >> > > > > > > table helps a lot but further compression on that already
> >> compact
> >> > > > > format
> >> > > > > > > would yield only marginal return.
> >> > > > > > >
> >> > > > > >
> >> > > > > > > So basically I feel we could get pretty far with a more
> >> compact
> >> > > field
> >> > > > > > > format for assignment and if we do that then we would
> >> potentially
> >> > > not
> >> > > > > > even
> >> > > > > > > want to do any compression.
> >> > > > > > >
> >> > > > > >
> >> > > > > > Also just wanted to add that this compression on the binary
> PAL
> >> did
> >> > > > help
> >> > > > > > but the compression ratio was obviously not as high as
> plaintext
> >> > > > > > compression.
> >> > > > > >
> >> > > > > >
> >> > > > > > >
> >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
> >> gwen@confluent.io
> >> > >
> >> > > > > wrote:
> >> > > > > > >
> >> > > > > > >> Regarding the change to the assignment field. It would be a
> >> > > protocol
> >> > > > > > bump,
> >> > > > > > >> otherwise consumers will not know how to parse the bytes
> the
> >> > > broker
> >> > > > is
> >> > > > > > >> returning, right?
> >> > > > > > >> Or did I misunderstand the suggestion?
> >> > > > > > >>
> >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
> >> > > wangguoz@gmail.com>
> >> > > > > > >> wrote:
> >> > > > > > >>
> >> > > > > > >> > I think for just solving issue 1), Jun's suggestion is
> >> > > sufficient
> >> > > > > and
> >> > > > > > >> > simple. So I'd prefer that approach.
> >> > > > > > >> >
> >> > > > > > >> > In addition, Jason's optimization on the assignment field
> >> > would
> >> > > be
> >> > > > > > good
> >> > > > > > >> for
> >> > > > > > >> > 2) and 3) as well, and I like that optimization for its
> >> > > simplicity
> >> > > > > and
> >> > > > > > >> no
> >> > > > > > >> > format change as well. And in the future I'm in favor of
> >> > > > considering
> >> > > > > > to
> >> > > > > > >> > change the in-memory cache format as Jiangjie suggested.
> >> > > > > > >> >
> >> > > > > > >> > Guozhang
> >> > > > > > >> >
> >> > > > > > >> >
> >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
> >> > > > becket.qin@gmail.com>
> >> > > > > > >> wrote:
> >> > > > > > >> >
> >> > > > > > >> > > Hi Jason,
> >> > > > > > >> > >
> >> > > > > > >> > > There are a few problems we want to solve here:
> >> > > > > > >> > > 1. The group metadata is too big to be appended to the
> >> log.
> >> > > > > > >> > > 2. Reduce the memory footprint on the broker
> >> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
> >> > > > > > >> > >
> >> > > > > > >> > > To solve (1), I like your idea of having separate
> >> messages
> >> > per
> >> > > > > > member.
> >> > > > > > >> > The
> >> > > > > > >> > > proposal (Onur's option 8) is to break metadata into
> >> small
> >> > > > records
> >> > > > > > in
> >> > > > > > >> the
> >> > > > > > >> > > same uncompressed message set so each record is small.
> I
> >> > agree
> >> > > > it
> >> > > > > > >> would
> >> > > > > > >> > be
> >> > > > > > >> > > ideal if we are able to store the metadata separately
> for
> >> > each
> >> > > > > > >> member. I
> >> > > > > > >> > > was also thinking about storing the metadata into
> >> multiple
> >> > > > > messages,
> >> > > > > > >> too.
> >> > > > > > >> > > What concerns me was that having multiple messages
> seems
> >> > > > breaking
> >> > > > > > the
> >> > > > > > >> > > atomicity. I am not sure how we are going to deal with
> >> the
> >> > > > > potential
> >> > > > > > >> > > issues. For example, What if group metadata is
> replicated
> >> > but
> >> > > > the
> >> > > > > > >> member
> >> > > > > > >> > > metadata is not? It might be fine depending on the
> >> > > > implementation
> >> > > > > > >> though,
> >> > > > > > >> > > but I am not sure.
> >> > > > > > >> > >
> >> > > > > > >> > > For (2) we want to store the metadata onto the disk,
> >> which
> >> > is
> >> > > > what
> >> > > > > > we
> >> > > > > > >> > have
> >> > > > > > >> > > to do anyway. The only question is in what format
> should
> >> we
> >> > > > store
> >> > > > > > >> them.
> >> > > > > > >> > >
> >> > > > > > >> > > To address (3) we want to have the metadata to be
> >> > compressed,
> >> > > > > which
> >> > > > > > is
> >> > > > > > >> > > contradict to the the above solution of (1).
> >> > > > > > >> > >
> >> > > > > > >> > > I think Jun's suggestion is probably still the
> simplest.
> >> To
> >> > > > avoid
> >> > > > > > >> > changing
> >> > > > > > >> > > the behavior for consumers, maybe we can do that only
> for
> >> > > > > > >> offset_topic,
> >> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is
> >> smaller
> >> > > than
> >> > > > > the
> >> > > > > > >> > > message size on the offset topic, we always return at
> >> least
> >> > > one
> >> > > > > full
> >> > > > > > >> > > message. This should avoid the unexpected problem on
> the
> >> > > client
> >> > > > > side
> >> > > > > > >> > > because supposedly only tools and brokers will fetch
> from
> >> > the
> >> > > > the
> >> > > > > > >> > internal
> >> > > > > > >> > > topics,
> >> > > > > > >> > >
> >> > > > > > >> > > As a modification to what you suggested, one solution I
> >> was
> >> > > > > thinking
> >> > > > > > >> was
> >> > > > > > >> > to
> >> > > > > > >> > > have multiple messages in a single compressed message.
> >> That
> >> > > > means
> >> > > > > > for
> >> > > > > > >> > > SyncGroupResponse we still need to read the entire
> >> > compressed
> >> > > > > > messages
> >> > > > > > >> > and
> >> > > > > > >> > > extract the inner messages, which seems not quite
> >> different
> >> > > from
> >> > > > > > >> having a
> >> > > > > > >> > > single message containing everything. But let me just
> >> put it
> >> > > > here
> >> > > > > > and
> >> > > > > > >> see
> >> > > > > > >> > > if that makes sense.
> >> > > > > > >> > >
> >> > > > > > >> > > We can have a map of GroupMetadataKey ->
> >> > > > GroupMetadataValueOffset.
> >> > > > > > >> > >
> >> > > > > > >> > > The GroupMetadataValue is stored in a compressed
> message.
> >> > The
> >> > > > > inner
> >> > > > > > >> > > messages are the following:
> >> > > > > > >> > >
> >> > > > > > >> > > Inner Message 0: Version GroupId Generation
> >> > > > > > >> > >
> >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can
> >> compress
> >> > > the
> >> > > > > > bytes
> >> > > > > > >> > here)
> >> > > > > > >> > >
> >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
> >> > > > > > >> > > ....
> >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
> >> > > > > > >> > >
> >> > > > > > >> > > The MemberMetadata format is the following:
> >> > > > > > >> > >   MemberMetadata => Version Generation ClientId Host
> >> > > > Subscription
> >> > > > > > >> > > Assignment
> >> > > > > > >> > >
> >> > > > > > >> > > So DescribeGroupResponse will just return the entire
> >> > > compressed
> >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return the
> >> > > > > > corresponding
> >> > > > > > >> > inner
> >> > > > > > >> > > message.
> >> > > > > > >> > >
> >> > > > > > >> > > Thanks,
> >> > > > > > >> > >
> >> > > > > > >> > > Jiangjie (Becket) Qin
> >> > > > > > >> > >
> >> > > > > > >> > >
> >> > > > > > >> > >
> >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson <
> >> > > > > > jason@confluent.io>
> >> > > > > > >> > > wrote:
> >> > > > > > >> > >
> >> > > > > > >> > > > Hey Becket,
> >> > > > > > >> > > >
> >> > > > > > >> > > > I like your idea to store only the offset for the
> group
> >> > > > metadata
> >> > > > > > in
> >> > > > > > >> > > memory.
> >> > > > > > >> > > > I think it would be safe to keep it in memory for a
> >> short
> >> > > time
> >> > > > > > after
> >> > > > > > >> > the
> >> > > > > > >> > > > rebalance completes, but after that, it's only real
> >> > purpose
> >> > > is
> >> > > > > to
> >> > > > > > >> > answer
> >> > > > > > >> > > > DescribeGroup requests, so your proposal makes a lot
> of
> >> > > sense
> >> > > > to
> >> > > > > > me.
> >> > > > > > >> > > >
> >> > > > > > >> > > > As for the specific problem with the size of the
> group
> >> > > > metadata
> >> > > > > > >> message
> >> > > > > > >> > > for
> >> > > > > > >> > > > the MM case, if we cannot succeed in reducing the
> size
> >> of
> >> > > the
> >> > > > > > >> > > > subscription/assignment (which I think is still
> >> probably
> >> > the
> >> > > > > best
> >> > > > > > >> > > > alternative if it can work), then I think there are
> >> some
> >> > > > options
> >> > > > > > for
> >> > > > > > >> > > > changing the message format (option #8 in Onur's
> >> initial
> >> > > > > e-mail).
> >> > > > > > >> > > > Currently, the key used for storing the group
> metadata
> >> is
> >> > > > this:
> >> > > > > > >> > > >
> >> > > > > > >> > > > GroupMetadataKey => Version GroupId
> >> > > > > > >> > > >
> >> > > > > > >> > > > And the value is something like this (some details
> >> > elided):
> >> > > > > > >> > > >
> >> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation
> >> > > > > [MemberMetadata]
> >> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
> >> Assignment
> >> > > > > > >> > > >
> >> > > > > > >> > > > I don't think we can change the key without a lot of
> >> pain,
> >> > > but
> >> > > > > it
> >> > > > > > >> seems
> >> > > > > > >> > > > like we can change the value format. Maybe we can
> take
> >> the
> >> > > > > > >> > > > subscription/assignment payloads out of the value and
> >> > > > introduce
> >> > > > > a
> >> > > > > > >> new
> >> > > > > > >> > > > "MemberMetadata" message for each member in the
> group.
> >> For
> >> > > > > > example:
> >> > > > > > >> > > >
> >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
> >> > > > > > >> > > >
> >> > > > > > >> > > > MemberMetadataValue => Version Generation ClientId
> Host
> >> > > > > > Subscription
> >> > > > > > >> > > > Assignment
> >> > > > > > >> > > >
> >> > > > > > >> > > > When a new generation is created, we would first
> write
> >> the
> >> > > > group
> >> > > > > > >> > metadata
> >> > > > > > >> > > > message which includes the generation and all of the
> >> > > > memberIds,
> >> > > > > > and
> >> > > > > > >> > then
> >> > > > > > >> > > > we'd write the member metadata messages. To answer
> the
> >> > > > > > DescribeGroup
> >> > > > > > >> > > > request, we'd read the group metadata at the cached
> >> offset
> >> > > > and,
> >> > > > > > >> > depending
> >> > > > > > >> > > > on the version, all of the following member metadata.
> >> This
> >> > > > would
> >> > > > > > be
> >> > > > > > >> > more
> >> > > > > > >> > > > complex to maintain, but it seems doable if it comes
> to
> >> > it.
> >> > > > > > >> > > >
> >> > > > > > >> > > > Thanks,
> >> > > > > > >> > > > Jason
> >> > > > > > >> > > >
> >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
> >> > > > > becket.qin@gmail.com
> >> > > > > > >
> >> > > > > > >> > > wrote:
> >> > > > > > >> > > >
> >> > > > > > >> > > > > It might worth thinking a little further. We have
> >> > > discussed
> >> > > > > this
> >> > > > > > >> > before
> >> > > > > > >> > > > > that we want to avoid holding all the group
> metadata
> >> in
> >> > > > > memory.
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > I am thinking about the following end state:
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > 1. Enable compression on the offset topic.
> >> > > > > > >> > > > > 2. Instead of holding the entire group metadata in
> >> > memory
> >> > > on
> >> > > > > the
> >> > > > > > >> > > brokers,
> >> > > > > > >> > > > > each broker only keeps a [group -> Offset] map, the
> >> > offset
> >> > > > > > points
> >> > > > > > >> to
> >> > > > > > >> > > the
> >> > > > > > >> > > > > message in the offset topic which holds the latest
> >> > > metadata
> >> > > > of
> >> > > > > > the
> >> > > > > > >> > > group.
> >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the offset
> >> topic
> >> > > > > > directly
> >> > > > > > >> > like
> >> > > > > > >> > > a
> >> > > > > > >> > > > > normal consumption, except that only exactly one
> >> message
> >> > > > will
> >> > > > > be
> >> > > > > > >> > > > returned.
> >> > > > > > >> > > > > 4. SyncGroupResponse will read the message, extract
> >> the
> >> > > > > > assignment
> >> > > > > > >> > part
> >> > > > > > >> > > > and
> >> > > > > > >> > > > > send back the partition assignment. We can compress
> >> the
> >> > > > > > partition
> >> > > > > > >> > > > > assignment before sends it out if we want.
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > Jiangjie (Becket) Qin
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason Gustafson <
> >> > > > > > >> jason@confluent.io
> >> > > > > > >> > >
> >> > > > > > >> > > > > wrote:
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression)
> >> basically
> >> > > do
> >> > > > > > this?
> >> > > > > > >> If
> >> > > > > > >> > > the
> >> > > > > > >> > > > > > topic
> >> > > > > > >> > > > > > > is a string and the topic is repeated
> throughout,
> >> > > won't
> >> > > > > > >> > compression
> >> > > > > > >> > > > > > > basically replace all repeated instances of it
> >> with
> >> > an
> >> > > > > index
> >> > > > > > >> > > > reference
> >> > > > > > >> > > > > to
> >> > > > > > >> > > > > > > the full string?
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > > Hey James, yeah, that's probably true, but keep
> in
> >> > mind
> >> > > > that
> >> > > > > > the
> >> > > > > > >> > > > > > compression happens on the broker side. It would
> be
> >> > nice
> >> > > > to
> >> > > > > > >> have a
> >> > > > > > >> > > more
> >> > > > > > >> > > > > > compact representation so that get some benefit
> >> over
> >> > the
> >> > > > > wire
> >> > > > > > as
> >> > > > > > >> > > well.
> >> > > > > > >> > > > > This
> >> > > > > > >> > > > > > seems to be less of a concern here, so the bigger
> >> > gains
> >> > > > are
> >> > > > > > >> > probably
> >> > > > > > >> > > > from
> >> > > > > > >> > > > > > reducing the number of partitions that need to be
> >> > listed
> >> > > > > > >> > > individually.
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > > -Jason
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur Karaman <
> >> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
> >> > > > > > >> > > > > > wrote:
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > > > When figuring out these optimizations, it's
> worth
> >> > > > keeping
> >> > > > > in
> >> > > > > > >> mind
> >> > > > > > >> > > the
> >> > > > > > >> > > > > > > improvements when the message is uncompressed
> vs
> >> > when
> >> > > > it's
> >> > > > > > >> > > > compressed.
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > When uncompressed:
> >> > > > > > >> > > > > > > Fixing the Assignment serialization to instead
> >> be a
> >> > > > topic
> >> > > > > > >> index
> >> > > > > > >> > > into
> >> > > > > > >> > > > > the
> >> > > > > > >> > > > > > > corresponding member's subscription list would
> >> > usually
> >> > > > be
> >> > > > > a
> >> > > > > > >> good
> >> > > > > > >> > > > thing.
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > I think the proposal is only worse when the
> topic
> >> > > names
> >> > > > > are
> >> > > > > > >> > small.
> >> > > > > > >> > > > The
> >> > > > > > >> > > > > > > Type.STRING we use in our protocol for the
> >> > > assignment's
> >> > > > > > >> > > > TOPIC_KEY_NAME
> >> > > > > > >> > > > > is
> >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so our
> >> strings
> >> > > are
> >> > > > > > first
> >> > > > > > >> > > > > prepended
> >> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > The new proposal does worse when:
> >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
> >> > index_type_size
> >> > > > > > >> > > > > > > in other words when:
> >> > > > > > >> > > > > > > utf_encoded_string_payload_size <
> >> index_type_size -
> >> > 2
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > If the index type ends up being Type.INT32,
> then
> >> the
> >> > > > > > proposal
> >> > > > > > >> is
> >> > > > > > >> > > > worse
> >> > > > > > >> > > > > > when
> >> > > > > > >> > > > > > > the topic is length 1.
> >> > > > > > >> > > > > > > If the index type ends up being Type.INT64,
> then
> >> the
> >> > > > > > proposal
> >> > > > > > >> is
> >> > > > > > >> > > > worse
> >> > > > > > >> > > > > > when
> >> > > > > > >> > > > > > > the topic is less than length 6.
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > When compressed:
> >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how
> >> things
> >> > > > change
> >> > > > > > when
> >> > > > > > >> > > > > > compression
> >> > > > > > >> > > > > > > comes into the picture. This would be worth
> >> > > > investigating.
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James Cheng <
> >> > > > > > >> > wushujames@gmail.com
> >> > > > > > >> > > >
> >> > > > > > >> > > > > > wrote:
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
> >> Gustafson <
> >> > > > > > >> > > > jason@confluent.io>
> >> > > > > > >> > > > > > > > wrote:
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay out
> the
> >> > > > > assignment
> >> > > > > > >> > without
> >> > > > > > >> > > > > > needing
> >> > > > > > >> > > > > > > > to
> >> > > > > > >> > > > > > > > > explicitly repeat the topic? For example,
> the
> >> > > leader
> >> > > > > > could
> >> > > > > > >> > sort
> >> > > > > > >> > > > the
> >> > > > > > >> > > > > > > > topics
> >> > > > > > >> > > > > > > > > for each member and just use an integer to
> >> > > represent
> >> > > > > the
> >> > > > > > >> > index
> >> > > > > > >> > > of
> >> > > > > > >> > > > > > each
> >> > > > > > >> > > > > > > > > topic within the sorted list (note this
> >> depends
> >> > on
> >> > > > the
> >> > > > > > >> > > > subscription
> >> > > > > > >> > > > > > > > > including the full topic list).
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]]
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other compression)
> >> > basically
> >> > > > do
> >> > > > > > >> this?
> >> > > > > > >> > If
> >> > > > > > >> > > > the
> >> > > > > > >> > > > > > > topic
> >> > > > > > >> > > > > > > > is a string and the topic is repeated
> >> throughout,
> >> > > > won't
> >> > > > > > >> > > compression
> >> > > > > > >> > > > > > > > basically replace all repeated instances of
> it
> >> > with
> >> > > an
> >> > > > > > index
> >> > > > > > >> > > > > reference
> >> > > > > > >> > > > > > to
> >> > > > > > >> > > > > > > > the full string?
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > > > -James
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > > > > You could even combine these two options so
> >> that
> >> > > you
> >> > > > > > have
> >> > > > > > >> > only
> >> > > > > > >> > > 3
> >> > > > > > >> > > > > > > integers
> >> > > > > > >> > > > > > > > > for each topic assignment:
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition
> >> > > MaxPartition]
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > There may even be better options with a
> >> little
> >> > > more
> >> > > > > > >> thought.
> >> > > > > > >> > > All
> >> > > > > > >> > > > of
> >> > > > > > >> > > > > > > this
> >> > > > > > >> > > > > > > > is
> >> > > > > > >> > > > > > > > > just part of the client-side protocol, so
> it
> >> > > > wouldn't
> >> > > > > > >> require
> >> > > > > > >> > > any
> >> > > > > > >> > > > > > > version
> >> > > > > > >> > > > > > > > > bumps on the broker. What do you think?
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > Thanks,
> >> > > > > > >> > > > > > > > > Jason
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM, Guozhang
> >> Wang <
> >> > > > > > >> > > > wangguoz@gmail.com
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > > > > > wrote:
> >> > > > > > >> > > > > > > > >
> >> > > > > > >> > > > > > > > >> The original concern is that regex may not
> >> be
> >> > > > > > efficiently
> >> > > > > > >> > > > > supported
> >> > > > > > >> > > > > > > > >> across-languages, but if there is a neat
> >> > > > workaround I
> >> > > > > > >> would
> >> > > > > > >> > > love
> >> > > > > > >> > > > > to
> >> > > > > > >> > > > > > > > learn.
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >> Guozhang
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM, Ismael
> >> Juma <
> >> > > > > > >> > > ismael@juma.me.uk
> >> > > > > > >> > > > >
> >> > > > > > >> > > > > > > wrote:
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>> Having said that, as a general point, I
> >> think
> >> > we
> >> > > > > > should
> >> > > > > > >> > > > consider
> >> > > > > > >> > > > > > > > >> supporting
> >> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol. It
> >> > requires
> >> > > > > some
> >> > > > > > >> > > thinking
> >> > > > > > >> > > > > for
> >> > > > > > >> > > > > > > > >>> cross-language support, but it seems
> >> > > surmountable
> >> > > > > and
> >> > > > > > it
> >> > > > > > >> > > could
> >> > > > > > >> > > > > make
> >> > > > > > >> > > > > > > > >> certain
> >> > > > > > >> > > > > > > > >>> operations a lot more efficient (the fact
> >> > that a
> >> > > > > basic
> >> > > > > > >> > regex
> >> > > > > > >> > > > > > > > subscription
> >> > > > > > >> > > > > > > > >>> causes the consumer to request metadata
> for
> >> > all
> >> > > > > topics
> >> > > > > > >> is
> >> > > > > > >> > not
> >> > > > > > >> > > > > > great).
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>> Ismael
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM,
> Guozhang
> >> > Wang
> >> > > <
> >> > > > > > >> > > > > > wangguoz@gmail.com>
> >> > > > > > >> > > > > > > > >>> wrote:
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing the
> >> > > handling
> >> > > > > > >> logics of
> >> > > > > > >> > > > > single
> >> > > > > > >> > > > > > > > large
> >> > > > > > >> > > > > > > > >>>> message on the consumer side.
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>> As for the case of "a single group
> >> > subscribing
> >> > > to
> >> > > > > > 3000
> >> > > > > > >> > > > topics",
> >> > > > > > >> > > > > > with
> >> > > > > > >> > > > > > > > >> 100
> >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
> >> reasonable
> >> > to
> >> > > me
> >> > > > > > (when
> >> > > > > > >> > > > storing
> >> > > > > > >> > > > > in
> >> > > > > > >> > > > > > > ZK,
> >> > > > > > >> > > > > > > > >> we
> >> > > > > > >> > > > > > > > >>>> also have the znode limit which is set
> to
> >> 1Mb
> >> > > by
> >> > > > > > >> default,
> >> > > > > > >> > > > though
> >> > > > > > >> > > > > > > > >>> admittedly
> >> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if we
> do
> >> > the
> >> > > > > change
> >> > > > > > >> as
> >> > > > > > >> > Jun
> >> > > > > > >> > > > > > > > suggested,
> >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure is
> OK
> >> I
> >> > > > think.
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>> Guozhang
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM, Onur
> >> > Karaman
> >> > > <
> >> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
> >> > > > > > >> > > > > > > > >>>>> wrote:
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>>> Results without compression:
> >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
> >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the tipping
> >> > point
> >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
> >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
> >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
> >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
> >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
> >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
> >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
> >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
> >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
> >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
> >> > > > > > >> > > > > > > > >>>>>
> >> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression
> shrinks
> >> > the
> >> > > > > > message
> >> > > > > > >> > size
> >> > > > > > >> > > by
> >> > > > > > >> > > > > 4x.
> >> > > > > > >> > > > > > > > >>>>>
> >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM, Jun
> Rao
> >> <
> >> > > > > > >> > jun@confluent.io
> >> > > > > > >> > > >
> >> > > > > > >> > > > > > wrote:
> >> > > > > > >> > > > > > > > >>>>>
> >> > > > > > >> > > > > > > > >>>>>> Onur,
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how we
> >> deal
> >> > > with
> >> > > > > the
> >> > > > > > >> case
> >> > > > > > >> > > > when a
> >> > > > > > >> > > > > > > > >>> message
> >> > > > > > >> > > > > > > > >>>> is
> >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today, if
> >> the
> >> > > fetch
> >> > > > > > size
> >> > > > > > >> is
> >> > > > > > >> > > > > smaller
> >> > > > > > >> > > > > > > > >> than
> >> > > > > > >> > > > > > > > >>>> the
> >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get
> stuck.
> >> > > > Instead,
> >> > > > > > we
> >> > > > > > >> can
> >> > > > > > >> > > > > simply
> >> > > > > > >> > > > > > > > >>> return
> >> > > > > > >> > > > > > > > >>>>> the
> >> > > > > > >> > > > > > > > >>>>>> full message if it's larger than the
> >> fetch
> >> > > size
> >> > > > > w/o
> >> > > > > > >> > > > requiring
> >> > > > > > >> > > > > > the
> >> > > > > > >> > > > > > > > >>>>> consumer
> >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size. On
> >> the
> >> > > > broker
> >> > > > > > >> side,
> >> > > > > > >> > to
> >> > > > > > >> > > > > serve
> >> > > > > > >> > > > > > a
> >> > > > > > >> > > > > > > > >>> fetch
> >> > > > > > >> > > > > > > > >>>>>> request, we already do an index lookup
> >> and
> >> > > then
> >> > > > > > scan
> >> > > > > > >> the
> >> > > > > > >> > > > log a
> >> > > > > > >> > > > > > bit
> >> > > > > > >> > > > > > > > >> to
> >> > > > > > >> > > > > > > > >>>>> find
> >> > > > > > >> > > > > > > > >>>>>> the message with the requested offset.
> >> We
> >> > can
> >> > > > > just
> >> > > > > > >> check
> >> > > > > > >> > > the
> >> > > > > > >> > > > > > size
> >> > > > > > >> > > > > > > > >> of
> >> > > > > > >> > > > > > > > >>>> that
> >> > > > > > >> > > > > > > > >>>>>> message and return the full message if
> >> its
> >> > > size
> >> > > > > is
> >> > > > > > >> > larger
> >> > > > > > >> > > > than
> >> > > > > > >> > > > > > the
> >> > > > > > >> > > > > > > > >>>> fetch
> >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is really
> for
> >> > > > > > performance
> >> > > > > > >> > > > > > optimization,
> >> > > > > > >> > > > > > > > >>> i.e.
> >> > > > > > >> > > > > > > > >>>>> in
> >> > > > > > >> > > > > > > > >>>>>> the common case, we will not return
> more
> >> > > bytes
> >> > > > > than
> >> > > > > > >> > fetch
> >> > > > > > >> > > > > size,
> >> > > > > > >> > > > > > > but
> >> > > > > > >> > > > > > > > >>> if
> >> > > > > > >> > > > > > > > >>>>>> there is a large message, we will
> return
> >> > more
> >> > > > > bytes
> >> > > > > > >> than
> >> > > > > > >> > > the
> >> > > > > > >> > > > > > > > >>> specified
> >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large
> messages
> >> are
> >> > > > rare.
> >> > > > > > >> So, it
> >> > > > > > >> > > > > > shouldn't
> >> > > > > > >> > > > > > > > >>>>> increase
> >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the client
> too
> >> > > much.
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>> Jun
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM, Onur
> >> > > Karaman <
> >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
> >> > > > > > >> > > > > > > > >>>>>> wrote:
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing some
> >> > tests
> >> > > on
> >> > > > > the
> >> > > > > > >> new
> >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
> >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more
> >> strenuous
> >> > use
> >> > > > > cases
> >> > > > > > >> like
> >> > > > > > >> > > > > > mirroring
> >> > > > > > >> > > > > > > > >>>>>> clusters
> >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and thought
> >> I'd
> >> > > share
> >> > > > > > >> > whatever I
> >> > > > > > >> > > > > have
> >> > > > > > >> > > > > > so
> >> > > > > > >> > > > > > > > >>>> far.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount of
> >> group
> >> > > > > > metadata
> >> > > > > > >> we
> >> > > > > > >> > > can
> >> > > > > > >> > > > > fit
> >> > > > > > >> > > > > > > > >> into
> >> > > > > > >> > > > > > > > >>>> one
> >> > > > > > >> > > > > > > > >>>>>>> message
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Some background:
> >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is implemented
> >> in
> >> > two
> >> > > > > > phases
> >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase that
> >> > > identifies
> >> > > > > > >> members
> >> > > > > > >> > of
> >> > > > > > >> > > > the
> >> > > > > > >> > > > > > > > >> group
> >> > > > > > >> > > > > > > > >>>> and
> >> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions.
> >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that waits
> for
> >> > the
> >> > > > > group
> >> > > > > > >> > leader
> >> > > > > > >> > > to
> >> > > > > > >> > > > > > > > >> decide
> >> > > > > > >> > > > > > > > >>>>> member
> >> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
> >> > > subscriptions
> >> > > > > > across
> >> > > > > > >> > the
> >> > > > > > >> > > > > group.
> >> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this decision
> >> > with a
> >> > > > > > >> > > > > SyncGroupRequest.
> >> > > > > > >> > > > > > > > >> The
> >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
> >> SyncGroupRequests
> >> > > by
> >> > > > > > >> appending
> >> > > > > > >> > > all
> >> > > > > > >> > > > > > group
> >> > > > > > >> > > > > > > > >>>> state
> >> > > > > > >> > > > > > > > >>>>>>> into a single message under the
> >> > > > > __consumer_offsets
> >> > > > > > >> > topic.
> >> > > > > > >> > > > > This
> >> > > > > > >> > > > > > > > >>>> message
> >> > > > > > >> > > > > > > > >>>>> is
> >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and contains
> each
> >> > > member
> >> > > > > > >> > > subscription
> >> > > > > > >> > > > > as
> >> > > > > > >> > > > > > > > >> well
> >> > > > > > >> > > > > > > > >>>> as
> >> > > > > > >> > > > > > > > >>>>>> the
> >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each member.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> The environment:
> >> > > > > > >> > > > > > > > >>>>>>> - one broker
> >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets partition
> >> > > > > > >> > > > > > > > >>>>>>> - offsets.topic.compression.codec=1
> //
> >> > this
> >> > > is
> >> > > > > > gzip
> >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending KAFKA-3718
> >> patch
> >> > > that
> >> > > > > > >> actually
> >> > > > > > >> > > > makes
> >> > > > > > >> > > > > > use
> >> > > > > > >> > > > > > > > >> of
> >> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec:
> >> > > > > > >> > > > > > > > >>>>>>
> >> https://github.com/apache/kafka/pull/1394
> >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an
> actual
> >> > > subset
> >> > > > > of
> >> > > > > > >> > topics
> >> > > > > > >> > > > from
> >> > > > > > >> > > > > > one
> >> > > > > > >> > > > > > > > >>> of
> >> > > > > > >> > > > > > > > >>>>> our
> >> > > > > > >> > > > > > > > >>>>>>> clusters.
> >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
> >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long on
> >> average
> >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number of
> >> > > consumers
> >> > > > > > each
> >> > > > > > >> > > > hardcoded
> >> > > > > > >> > > > > > > > >> with
> >> > > > > > >> > > > > > > > >>>> all
> >> > > > > > >> > > > > > > > >>>>>> the
> >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests more
> >> > > consistent.
> >> > > > > > >> > > wildcarding
> >> > > > > > >> > > > > with
> >> > > > > > >> > > > > > > > >> .*
> >> > > > > > >> > > > > > > > >>>>> should
> >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
> >> subscription
> >> > > > hits
> >> > > > > > the
> >> > > > > > >> > > > > coordinator
> >> > > > > > >> > > > > > > > >> as
> >> > > > > > >> > > > > > > > >>>> the
> >> > > > > > >> > > > > > > > >>>>>>> subscription has already been fully
> >> > expanded
> >> > > > out
> >> > > > > > to
> >> > > > > > >> the
> >> > > > > > >> > > > list
> >> > > > > > >> > > > > of
> >> > > > > > >> > > > > > > > >>>> topics
> >> > > > > > >> > > > > > > > >>>>> by
> >> > > > > > >> > > > > > > > >>>>>>> the consumers.
> >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to
> >> Log.scala
> >> > to
> >> > > > > print
> >> > > > > > >> out
> >> > > > > > >> > the
> >> > > > > > >> > > > > > message
> >> > > > > > >> > > > > > > > >>>> sizes
> >> > > > > > >> > > > > > > > >>>>>>> after compression
> >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all and
> >> auto
> >> > > > commits
> >> > > > > > are
> >> > > > > > >> > > > > disabled.
> >> > > > > > >> > > > > > > > >> The
> >> > > > > > >> > > > > > > > >>>> only
> >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added is
> >> the
> >> > > > > > >> > > __consumer_offsets
> >> > > > > > >> > > > > > topic
> >> > > > > > >> > > > > > > > >>> and
> >> > > > > > >> > > > > > > > >>>>>>> they're only from storing group
> >> metadata
> >> > > while
> >> > > > > > >> > processing
> >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Results:
> >> > > > > > >> > > > > > > > >>>>>>> The results below show that we exceed
> >> the
> >> > > > > 1000012
> >> > > > > > >> byte
> >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit
> >> > relatively
> >> > > > > > quickly
> >> > > > > > >> > > > (between
> >> > > > > > >> > > > > > > > >> 30-40
> >> > > > > > >> > > > > > > > >>>>>>> consumers):
> >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the
> >> tipping
> >> > > point
> >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
> >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is pretty
> >> > > gradual.
> >> > > > > > >> Plotting
> >> > > > > > >> > > the
> >> > > > > > >> > > > > > > > >> points
> >> > > > > > >> > > > > > > > >>>>> makes
> >> > > > > > >> > > > > > > > >>>>>> it
> >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the number
> of
> >> > > > > consumers:
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > >
> >> > > > > > >> > > >
> >> > > > > > >> > >
> >> > > > > > >> >
> >> > > > > > >>
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers aren't
> >> > averages
> >> > > > or
> >> > > > > > >> medians
> >> > > > > > >> > > or
> >> > > > > > >> > > > > > > > >> anything
> >> > > > > > >> > > > > > > > >>>>> like
> >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size from a
> >> given
> >> > > > run.
> >> > > > > I
> >> > > > > > >> did
> >> > > > > > >> > run
> >> > > > > > >> > > > > them
> >> > > > > > >> > > > > > a
> >> > > > > > >> > > > > > > > >>> few
> >> > > > > > >> > > > > > > > >>>>>> times
> >> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Impact:
> >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
> >> > > > __consumer_offsets
> >> > > > > > >> topic
> >> > > > > > >> > > with
> >> > > > > > >> > > > > my
> >> > > > > > >> > > > > > > > >>>> pending
> >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the AwaitingSync
> >> phase
> >> > of
> >> > > > the
> >> > > > > > >> group
> >> > > > > > >> > > fails
> >> > > > > > >> > > > > > with
> >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This means
> the
> >> > > > combined
> >> > > > > > >> size
> >> > > > > > >> > of
> >> > > > > > >> > > > each
> >> > > > > > >> > > > > > > > >>>> member's
> >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments
> exceeded
> >> the
> >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
> >> > > > > > >> > > > > > > > >>>>> of
> >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up
> dying.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Options:
> >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the number
> of
> >> > > > consumers
> >> > > > > > in
> >> > > > > > >> the
> >> > > > > > >> > > > > group.
> >> > > > > > >> > > > > > > > >> This
> >> > > > > > >> > > > > > > > >>>>> isn't
> >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more
> >> > strenuous
> >> > > > use
> >> > > > > > >> cases
> >> > > > > > >> > > like
> >> > > > > > >> > > > > > > > >>>> MirrorMaker
> >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
> >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group
> into
> >> > > smaller
> >> > > > > > >> groups
> >> > > > > > >> > > which
> >> > > > > > >> > > > > > > > >>> together
> >> > > > > > >> > > > > > > > >>>>> will
> >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics. This
> >> > gives
> >> > > > each
> >> > > > > > >> group
> >> > > > > > >> > > > > member a
> >> > > > > > >> > > > > > > > >>>> smaller
> >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics
> >> starting
> >> > > with
> >> > > > > a-m
> >> > > > > > >> while
> >> > > > > > >> > > g2
> >> > > > > > >> > > > > has
> >> > > > > > >> > > > > > > > >>> topics
> >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be
> >> > > operationally
> >> > > > > > >> painful
> >> > > > > > >> > to
> >> > > > > > >> > > > > > manage.
> >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the topics
> >> among
> >> > > > members
> >> > > > > > of
> >> > > > > > >> the
> >> > > > > > >> > > > > group.
> >> > > > > > >> > > > > > > > >>> Again
> >> > > > > > >> > > > > > > > >>>>> this
> >> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller
> >> > > > subscription.
> >> > > > > > This
> >> > > > > > >> > > would
> >> > > > > > >> > > > > also
> >> > > > > > >> > > > > > > > >> be
> >> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage.
> >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
> >> > > > > > >> KafkaConfig.messageMaxBytes
> >> > > > > > >> > (a
> >> > > > > > >> > > > > > > > >>> topic-level
> >> > > > > > >> > > > > > > > >>>>>>> config) and
> >> > KafkaConfig.replicaFetchMaxBytes
> >> > > > (a
> >> > > > > > >> > > > broker-level
> >> > > > > > >> > > > > > > > >>> config).
> >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just the
> >> > > > > > >> __consumer_offsets
> >> > > > > > >> > > > topic
> >> > > > > > >> > > > > > > > >> seems
> >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping up
> the
> >> > > > > > broker-level
> >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
> >> > > > > > >> > > > > > > > >>>>>>> would probably need more attention.
> >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
> >> > compression
> >> > > > > > codecs.
> >> > > > > > >> > Based
> >> > > > > > >> > > > on
> >> > > > > > >> > > > > 2
> >> > > > > > >> > > > > > > > >>>> minutes
> >> > > > > > >> > > > > > > > >>>>> of
> >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and
> snappy
> >> are
> >> > > > > faster
> >> > > > > > >> than
> >> > > > > > >> > > gzip
> >> > > > > > >> > > > > but
> >> > > > > > >> > > > > > > > >>> have
> >> > > > > > >> > > > > > > > >>>>>> worse
> >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably won't
> >> help.
> >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support
> >> sending
> >> > > the
> >> > > > > > regex
> >> > > > > > >> > over
> >> > > > > > >> > > > the
> >> > > > > > >> > > > > > wire
> >> > > > > > >> > > > > > > > >>>>> instead
> >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
> >> > subscriptions. I
> >> > > > > think
> >> > > > > > >> > people
> >> > > > > > >> > > > > said
> >> > > > > > >> > > > > > in
> >> > > > > > >> > > > > > > > >>> the
> >> > > > > > >> > > > > > > > >>>>>> past
> >> > > > > > >> > > > > > > > >>>>>>> that different languages have subtle
> >> > > > differences
> >> > > > > > in
> >> > > > > > >> > > regex,
> >> > > > > > >> > > > so
> >> > > > > > >> > > > > > > > >> this
> >> > > > > > >> > > > > > > > >>>>>> doesn't
> >> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language
> groups.
> >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe we
> can
> >> > > reverse
> >> > > > > the
> >> > > > > > >> > > mapping?
> >> > > > > > >> > > > > > > > >> Instead
> >> > > > > > >> > > > > > > > >>>> of
> >> > > > > > >> > > > > > > > >>>>>>> mapping from member to subscriptions,
> >> we
> >> > can
> >> > > > > map a
> >> > > > > > >> > > > > subscription
> >> > > > > > >> > > > > > > > >> to
> >> > > > > > >> > > > > > > > >>> a
> >> > > > > > >> > > > > > > > >>>>> list
> >> > > > > > >> > > > > > > > >>>>>>> of members.
> >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe we
> can
> >> try
> >> > > to
> >> > > > > > break
> >> > > > > > >> > apart
> >> > > > > > >> > > > the
> >> > > > > > >> > > > > > > > >>>>>> subscription
> >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
> >> > > SyncGroupRequest
> >> > > > > > into
> >> > > > > > >> > > > multiple
> >> > > > > > >> > > > > > > > >>> records?
> >> > > > > > >> > > > > > > > >>>>>> They
> >> > > > > > >> > > > > > > > >>>>>>> can still go to the same message set
> >> and
> >> > get
> >> > > > > > >> appended
> >> > > > > > >> > > > > together.
> >> > > > > > >> > > > > > > > >>> This
> >> > > > > > >> > > > > > > > >>>>> way
> >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment size,
> >> which
> >> > > > > shouldn't
> >> > > > > > >> be a
> >> > > > > > >> > > > > > problem.
> >> > > > > > >> > > > > > > > >>> This
> >> > > > > > >> > > > > > > > >>>>> can
> >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because we're
> >> > > currently
> >> > > > > > >> keying
> >> > > > > > >> > > these
> >> > > > > > >> > > > > > > > >>> messages
> >> > > > > > >> > > > > > > > >>>> on
> >> > > > > > >> > > > > > > > >>>>>> the
> >> > > > > > >> > > > > > > > >>>>>>> group, so I think records from the
> same
> >> > > > > rebalance
> >> > > > > > >> might
> >> > > > > > >> > > > > > > > >>> accidentally
> >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
> >> understanding
> >> > of
> >> > > > > > >> compaction
> >> > > > > > >> > > > isn't
> >> > > > > > >> > > > > > > > >> that
> >> > > > > > >> > > > > > > > >>>>> great.
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> Todo:
> >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun the
> >> tests
> >> > > > with
> >> > > > > no
> >> > > > > > >> > > > > compression
> >> > > > > > >> > > > > > > > >> just
> >> > > > > > >> > > > > > > > >>>> to
> >> > > > > > >> > > > > > > > >>>>>> see
> >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's
> >> getting
> >> > > > late.
> >> > > > > > >> Maybe
> >> > > > > > >> > > > > tomorrow?
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>> - Onur
> >> > > > > > >> > > > > > > > >>>>>>>
> >> > > > > > >> > > > > > > > >>>>>>
> >> > > > > > >> > > > > > > > >>>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>> --
> >> > > > > > >> > > > > > > > >>>> -- Guozhang
> >> > > > > > >> > > > > > > > >>>>
> >> > > > > > >> > > > > > > > >>>
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > > >> --
> >> > > > > > >> > > > > > > > >> -- Guozhang
> >> > > > > > >> > > > > > > > >>
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > > >
> >> > > > > > >> > > > > > >
> >> > > > > > >> > > > > >
> >> > > > > > >> > > > >
> >> > > > > > >> > > >
> >> > > > > > >> > >
> >> > > > > > >> >
> >> > > > > > >> >
> >> > > > > > >> >
> >> > > > > > >> > --
> >> > > > > > >> > -- Guozhang
> >> > > > > > >> >
> >> > > > > > >>
> >> > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> >
> >
>

Re: [DISCUSS] scalability limits in the coordinator

[Onur Karaman <ok...@linkedin.com.INVALID>]

Maybe another approach can be to add a new
"offsets.replica.fetch.max.bytes" config on the brokers.

On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <ok...@linkedin.com> wrote:

> I made a PR with a tweak to Jun's/Becket's proposal:
> https://github.com/apache/kafka/pull/1484
>
> It just tweaks the fetch behavior specifically for replicas fetching from
> the __consumer_offsets topic when the fetcher's "replica.fetch.max.bytes"
> is less than the __consumer_offset leader's "message.max.bytes" to take the
> max of the two.
>
> I'm honestly not that happy with this solution, as I'd rather not change
> the "replica.fetch.max.bytes" config from being a limit to a
> recommendation. I'd definitely be happy to hear other alternatives!
>
> On Sun, May 29, 2016 at 1:57 PM, Onur Karaman <
> onurkaraman.apache@gmail.com> wrote:
>
>> Sorry I know next to nothing about Kafka Connect. I didn't understand the
>> Kafka Connect / MM idea you brought up. Can you go into more detail?
>>
>> Otherwise I think our remaining options are:
>> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for
>> __consumer_offsets topic and change the fetch behavior when message size
>> is
>> larger than fetch size
>> - option 6: support sending the regex over the wire instead of the fully
>> expanded topic subscriptions. This should cut down the message size from
>> the subscription side. Again this only helps when pattern-based
>> subscriptions are done.
>>
>> minor correction to an earlier comment I made regarding the message size:
>> message size ~ sum(s_i + a_i for i in range [1, |C|])
>>
>> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <ja...@confluent.io>
>> wrote:
>>
>> > Hey Onur,
>> >
>> > Thanks for the investigation. It seems the conclusion is that the
>> compact
>> > format helps, but perhaps not enough to justify adding a new assignment
>> > schema? I'm not sure there's much more room for savings unless we change
>> > something more fundamental in the assignment approach. We spent some
>> time
>> > thinking before about whether we could let the consumers compute their
>> > assignment locally from a smaller set of information, but the difficulty
>> > (I'm sure you remember) is reaching consensus on topic metadata. Kafka
>> > Connect has a similar problem where all the workers need to agree on
>> > connector configurations. Since all configs are stored in a single topic
>> > partition, the approach we take there is to propagate the offset in the
>> > assignment protocol. Not sure if we could do something similar for MM...
>> > Anyway, it seems like the best workaround at the moment is Jun's initial
>> > suggestion. What do you think?
>> >
>> > -Jason
>> >
>> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman <
>> > onurkaraman.apache@gmail.com
>> > > wrote:
>> >
>> > > I gave the topic index assignment trick a try against the same
>> > environment.
>> > > The implementation just changed the assignment serialization and
>> > > deserialization logic. It didn't change SyncGroupResponse, meaning it
>> > > continues to exclude the subscription from the SyncGroupResponse and
>> > > assumes the member has kept track of its last subscription.
>> > >
>> > > Assignment topic indexing with compression:
>> > > 1 consumer 34346 bytes
>> > > 5 consumers 177687 bytes
>> > > 10 consumers 331897 bytes
>> > > 20 consumers 572467 bytes
>> > > 30 consumers 811269 bytes
>> > > 40 consumers 1047188 bytes * the tipping point
>> > > 50 consumers 1290092 bytes
>> > > 60 consumers 1527806 bytes
>> > > 70 consumers 1769259 bytes
>> > > 80 consumers 2000118 bytes
>> > > 90 consumers 2244392 bytes
>> > > 100 consumers 2482415 bytes
>> > >
>> > > Assignment topic indexing without compression:
>> > > 1 consumer 211904 bytes
>> > > 5 consumers 677184 bytes
>> > > 10 consumers 1211154 bytes * the tipping point
>> > > 20 consumers 2136196 bytes
>> > > 30 consumers 3061238 bytes
>> > > 40 consumers 3986280 bytes
>> > > 50 consumers 4911322 bytes
>> > > 60 consumers 5836284 bytes
>> > > 70 consumers 6761246 bytes
>> > > 80 consumers 7686208 bytes
>> > > 90 consumers 8611170 bytes
>> > > 100 consumers 9536132 bytes
>> > >
>> > > Assignment topic indexing seems to reduce the size by 500KB without
>> > > compression and 80KB with compression. So assignment topic indexing
>> makes
>> > > some difference in both with and without compression but in our case
>> was
>> > > not nearly enough.
>> > >
>> > > This can be explained by the fact that we aren't actually hitting the
>> > worst
>> > > case scenario of each consumer being assigned a partition from every
>> > topic.
>> > > The reason is simple: a topic can only fully span all the consumers
>> if it
>> > > has at least as many partitions as there are consumers. Given that
>> there
>> > > are 8 partitions per topic and we have 100 consumers, it makes sense
>> that
>> > > we aren't close to this worse case scenario where topic indexing would
>> > make
>> > > a bigger difference.
>> > >
>> > > I tweaked the group leader's assignment code to print out the
>> assignments
>> > > and found that each consumer was getting either 238 or 239 partitions.
>> > Each
>> > > of these partitions were from unique topics. So the consumers were
>> really
>> > > getting partitions from 239 topics instead of the full worst case
>> > scenario
>> > > of 3000 topics.
>> > >
>> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson <ja...@confluent.io>
>> > > wrote:
>> > >
>> > > > Gwen, Joel:
>> > > >
>> > > > That's correct. The protocol does allow us to give an assignor its
>> own
>> > > > assignment schema, but I think this will require a couple internal
>> > > changes
>> > > > to the consumer to make use of the full generality.
>> > > >
>> > > > One thing I'm a little uncertain about is whether we should use a
>> > > different
>> > > > protocol type. For a little context, the group membership protocol
>> > allows
>> > > > the client to provide a "protocol type" when joining the group to
>> > ensure
>> > > > that all members have some basic semantic compatibility. For
>> example,
>> > the
>> > > > consumer uses "consumer" and Kafka Connect uses "connect." Currently
>> > all
>> > > > assignors using the "consumer" protocol share a common schema for
>> > > > representing subscriptions and assignment. This is convenient for
>> tools
>> > > > (like consumer-groups.sh) since they just need to know how to parse
>> the
>> > > > "consumer" protocol type without knowing anything about the
>> assignors.
>> > So
>> > > > introducing another schema would break that assumption and we'd need
>> > > those
>> > > > tools to do assignor-specific parsing. Maybe this is OK?
>> Alternatively,
>> > > we
>> > > > could use a separate protocol type (e.g. "compact-consumer"), but
>> that
>> > > > seems less than desirable.
>> > > >
>> > > > Thanks,
>> > > > Jason
>> > > >
>> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <gw...@confluent.io>
>> > > wrote:
>> > > >
>> > > > > ah, right - we can add as many strategies as we want.
>> > > > >
>> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy <jjkoshy.w@gmail.com
>> >
>> > > > wrote:
>> > > > >
>> > > > > > > Yes it would be a protocol bump.
>> > > > > > >
>> > > > > >
>> > > > > > Sorry - I'm officially confused. I think it may not be required
>> -
>> > > since
>> > > > > the
>> > > > > > more compact format would be associated with a new assignment
>> > > strategy
>> > > > -
>> > > > > > right?
>> > > > > >
>> > > > > >
>> > > > > > > smaller than the plaintext PAL, but the post-compressed binary
>> > PAL
>> > > is
>> > > > > > just
>> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW using
>> a
>> > > > symbol
>> > > > > > > table helps a lot but further compression on that already
>> compact
>> > > > > format
>> > > > > > > would yield only marginal return.
>> > > > > > >
>> > > > > >
>> > > > > > > So basically I feel we could get pretty far with a more
>> compact
>> > > field
>> > > > > > > format for assignment and if we do that then we would
>> potentially
>> > > not
>> > > > > > even
>> > > > > > > want to do any compression.
>> > > > > > >
>> > > > > >
>> > > > > > Also just wanted to add that this compression on the binary PAL
>> did
>> > > > help
>> > > > > > but the compression ratio was obviously not as high as plaintext
>> > > > > > compression.
>> > > > > >
>> > > > > >
>> > > > > > >
>> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira <
>> gwen@confluent.io
>> > >
>> > > > > wrote:
>> > > > > > >
>> > > > > > >> Regarding the change to the assignment field. It would be a
>> > > protocol
>> > > > > > bump,
>> > > > > > >> otherwise consumers will not know how to parse the bytes the
>> > > broker
>> > > > is
>> > > > > > >> returning, right?
>> > > > > > >> Or did I misunderstand the suggestion?
>> > > > > > >>
>> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang <
>> > > wangguoz@gmail.com>
>> > > > > > >> wrote:
>> > > > > > >>
>> > > > > > >> > I think for just solving issue 1), Jun's suggestion is
>> > > sufficient
>> > > > > and
>> > > > > > >> > simple. So I'd prefer that approach.
>> > > > > > >> >
>> > > > > > >> > In addition, Jason's optimization on the assignment field
>> > would
>> > > be
>> > > > > > good
>> > > > > > >> for
>> > > > > > >> > 2) and 3) as well, and I like that optimization for its
>> > > simplicity
>> > > > > and
>> > > > > > >> no
>> > > > > > >> > format change as well. And in the future I'm in favor of
>> > > > considering
>> > > > > > to
>> > > > > > >> > change the in-memory cache format as Jiangjie suggested.
>> > > > > > >> >
>> > > > > > >> > Guozhang
>> > > > > > >> >
>> > > > > > >> >
>> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin <
>> > > > becket.qin@gmail.com>
>> > > > > > >> wrote:
>> > > > > > >> >
>> > > > > > >> > > Hi Jason,
>> > > > > > >> > >
>> > > > > > >> > > There are a few problems we want to solve here:
>> > > > > > >> > > 1. The group metadata is too big to be appended to the
>> log.
>> > > > > > >> > > 2. Reduce the memory footprint on the broker
>> > > > > > >> > > 3. Reduce the bytes transferred over the wire.
>> > > > > > >> > >
>> > > > > > >> > > To solve (1), I like your idea of having separate
>> messages
>> > per
>> > > > > > member.
>> > > > > > >> > The
>> > > > > > >> > > proposal (Onur's option 8) is to break metadata into
>> small
>> > > > records
>> > > > > > in
>> > > > > > >> the
>> > > > > > >> > > same uncompressed message set so each record is small. I
>> > agree
>> > > > it
>> > > > > > >> would
>> > > > > > >> > be
>> > > > > > >> > > ideal if we are able to store the metadata separately for
>> > each
>> > > > > > >> member. I
>> > > > > > >> > > was also thinking about storing the metadata into
>> multiple
>> > > > > messages,
>> > > > > > >> too.
>> > > > > > >> > > What concerns me was that having multiple messages seems
>> > > > breaking
>> > > > > > the
>> > > > > > >> > > atomicity. I am not sure how we are going to deal with
>> the
>> > > > > potential
>> > > > > > >> > > issues. For example, What if group metadata is replicated
>> > but
>> > > > the
>> > > > > > >> member
>> > > > > > >> > > metadata is not? It might be fine depending on the
>> > > > implementation
>> > > > > > >> though,
>> > > > > > >> > > but I am not sure.
>> > > > > > >> > >
>> > > > > > >> > > For (2) we want to store the metadata onto the disk,
>> which
>> > is
>> > > > what
>> > > > > > we
>> > > > > > >> > have
>> > > > > > >> > > to do anyway. The only question is in what format should
>> we
>> > > > store
>> > > > > > >> them.
>> > > > > > >> > >
>> > > > > > >> > > To address (3) we want to have the metadata to be
>> > compressed,
>> > > > > which
>> > > > > > is
>> > > > > > >> > > contradict to the the above solution of (1).
>> > > > > > >> > >
>> > > > > > >> > > I think Jun's suggestion is probably still the simplest.
>> To
>> > > > avoid
>> > > > > > >> > changing
>> > > > > > >> > > the behavior for consumers, maybe we can do that only for
>> > > > > > >> offset_topic,
>> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is
>> smaller
>> > > than
>> > > > > the
>> > > > > > >> > > message size on the offset topic, we always return at
>> least
>> > > one
>> > > > > full
>> > > > > > >> > > message. This should avoid the unexpected problem on the
>> > > client
>> > > > > side
>> > > > > > >> > > because supposedly only tools and brokers will fetch from
>> > the
>> > > > the
>> > > > > > >> > internal
>> > > > > > >> > > topics,
>> > > > > > >> > >
>> > > > > > >> > > As a modification to what you suggested, one solution I
>> was
>> > > > > thinking
>> > > > > > >> was
>> > > > > > >> > to
>> > > > > > >> > > have multiple messages in a single compressed message.
>> That
>> > > > means
>> > > > > > for
>> > > > > > >> > > SyncGroupResponse we still need to read the entire
>> > compressed
>> > > > > > messages
>> > > > > > >> > and
>> > > > > > >> > > extract the inner messages, which seems not quite
>> different
>> > > from
>> > > > > > >> having a
>> > > > > > >> > > single message containing everything. But let me just
>> put it
>> > > > here
>> > > > > > and
>> > > > > > >> see
>> > > > > > >> > > if that makes sense.
>> > > > > > >> > >
>> > > > > > >> > > We can have a map of GroupMetadataKey ->
>> > > > GroupMetadataValueOffset.
>> > > > > > >> > >
>> > > > > > >> > > The GroupMetadataValue is stored in a compressed message.
>> > The
>> > > > > inner
>> > > > > > >> > > messages are the following:
>> > > > > > >> > >
>> > > > > > >> > > Inner Message 0: Version GroupId Generation
>> > > > > > >> > >
>> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can
>> compress
>> > > the
>> > > > > > bytes
>> > > > > > >> > here)
>> > > > > > >> > >
>> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2
>> > > > > > >> > > ....
>> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N
>> > > > > > >> > >
>> > > > > > >> > > The MemberMetadata format is the following:
>> > > > > > >> > >   MemberMetadata => Version Generation ClientId Host
>> > > > Subscription
>> > > > > > >> > > Assignment
>> > > > > > >> > >
>> > > > > > >> > > So DescribeGroupResponse will just return the entire
>> > > compressed
>> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return the
>> > > > > > corresponding
>> > > > > > >> > inner
>> > > > > > >> > > message.
>> > > > > > >> > >
>> > > > > > >> > > Thanks,
>> > > > > > >> > >
>> > > > > > >> > > Jiangjie (Becket) Qin
>> > > > > > >> > >
>> > > > > > >> > >
>> > > > > > >> > >
>> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson <
>> > > > > > jason@confluent.io>
>> > > > > > >> > > wrote:
>> > > > > > >> > >
>> > > > > > >> > > > Hey Becket,
>> > > > > > >> > > >
>> > > > > > >> > > > I like your idea to store only the offset for the group
>> > > > metadata
>> > > > > > in
>> > > > > > >> > > memory.
>> > > > > > >> > > > I think it would be safe to keep it in memory for a
>> short
>> > > time
>> > > > > > after
>> > > > > > >> > the
>> > > > > > >> > > > rebalance completes, but after that, it's only real
>> > purpose
>> > > is
>> > > > > to
>> > > > > > >> > answer
>> > > > > > >> > > > DescribeGroup requests, so your proposal makes a lot of
>> > > sense
>> > > > to
>> > > > > > me.
>> > > > > > >> > > >
>> > > > > > >> > > > As for the specific problem with the size of the group
>> > > > metadata
>> > > > > > >> message
>> > > > > > >> > > for
>> > > > > > >> > > > the MM case, if we cannot succeed in reducing the size
>> of
>> > > the
>> > > > > > >> > > > subscription/assignment (which I think is still
>> probably
>> > the
>> > > > > best
>> > > > > > >> > > > alternative if it can work), then I think there are
>> some
>> > > > options
>> > > > > > for
>> > > > > > >> > > > changing the message format (option #8 in Onur's
>> initial
>> > > > > e-mail).
>> > > > > > >> > > > Currently, the key used for storing the group metadata
>> is
>> > > > this:
>> > > > > > >> > > >
>> > > > > > >> > > > GroupMetadataKey => Version GroupId
>> > > > > > >> > > >
>> > > > > > >> > > > And the value is something like this (some details
>> > elided):
>> > > > > > >> > > >
>> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation
>> > > > > [MemberMetadata]
>> > > > > > >> > > >   MemberMetadata => ClientId Host Subscription
>> Assignment
>> > > > > > >> > > >
>> > > > > > >> > > > I don't think we can change the key without a lot of
>> pain,
>> > > but
>> > > > > it
>> > > > > > >> seems
>> > > > > > >> > > > like we can change the value format. Maybe we can take
>> the
>> > > > > > >> > > > subscription/assignment payloads out of the value and
>> > > > introduce
>> > > > > a
>> > > > > > >> new
>> > > > > > >> > > > "MemberMetadata" message for each member in the group.
>> For
>> > > > > > example:
>> > > > > > >> > > >
>> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId
>> > > > > > >> > > >
>> > > > > > >> > > > MemberMetadataValue => Version Generation ClientId Host
>> > > > > > Subscription
>> > > > > > >> > > > Assignment
>> > > > > > >> > > >
>> > > > > > >> > > > When a new generation is created, we would first write
>> the
>> > > > group
>> > > > > > >> > metadata
>> > > > > > >> > > > message which includes the generation and all of the
>> > > > memberIds,
>> > > > > > and
>> > > > > > >> > then
>> > > > > > >> > > > we'd write the member metadata messages. To answer the
>> > > > > > DescribeGroup
>> > > > > > >> > > > request, we'd read the group metadata at the cached
>> offset
>> > > > and,
>> > > > > > >> > depending
>> > > > > > >> > > > on the version, all of the following member metadata.
>> This
>> > > > would
>> > > > > > be
>> > > > > > >> > more
>> > > > > > >> > > > complex to maintain, but it seems doable if it comes to
>> > it.
>> > > > > > >> > > >
>> > > > > > >> > > > Thanks,
>> > > > > > >> > > > Jason
>> > > > > > >> > > >
>> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin <
>> > > > > becket.qin@gmail.com
>> > > > > > >
>> > > > > > >> > > wrote:
>> > > > > > >> > > >
>> > > > > > >> > > > > It might worth thinking a little further. We have
>> > > discussed
>> > > > > this
>> > > > > > >> > before
>> > > > > > >> > > > > that we want to avoid holding all the group metadata
>> in
>> > > > > memory.
>> > > > > > >> > > > >
>> > > > > > >> > > > > I am thinking about the following end state:
>> > > > > > >> > > > >
>> > > > > > >> > > > > 1. Enable compression on the offset topic.
>> > > > > > >> > > > > 2. Instead of holding the entire group metadata in
>> > memory
>> > > on
>> > > > > the
>> > > > > > >> > > brokers,
>> > > > > > >> > > > > each broker only keeps a [group -> Offset] map, the
>> > offset
>> > > > > > points
>> > > > > > >> to
>> > > > > > >> > > the
>> > > > > > >> > > > > message in the offset topic which holds the latest
>> > > metadata
>> > > > of
>> > > > > > the
>> > > > > > >> > > group.
>> > > > > > >> > > > > 3. DescribeGroupResponse will read from the offset
>> topic
>> > > > > > directly
>> > > > > > >> > like
>> > > > > > >> > > a
>> > > > > > >> > > > > normal consumption, except that only exactly one
>> message
>> > > > will
>> > > > > be
>> > > > > > >> > > > returned.
>> > > > > > >> > > > > 4. SyncGroupResponse will read the message, extract
>> the
>> > > > > > assignment
>> > > > > > >> > part
>> > > > > > >> > > > and
>> > > > > > >> > > > > send back the partition assignment. We can compress
>> the
>> > > > > > partition
>> > > > > > >> > > > > assignment before sends it out if we want.
>> > > > > > >> > > > >
>> > > > > > >> > > > > Jiangjie (Becket) Qin
>> > > > > > >> > > > >
>> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason Gustafson <
>> > > > > > >> jason@confluent.io
>> > > > > > >> > >
>> > > > > > >> > > > > wrote:
>> > > > > > >> > > > >
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression)
>> basically
>> > > do
>> > > > > > this?
>> > > > > > >> If
>> > > > > > >> > > the
>> > > > > > >> > > > > > topic
>> > > > > > >> > > > > > > is a string and the topic is repeated throughout,
>> > > won't
>> > > > > > >> > compression
>> > > > > > >> > > > > > > basically replace all repeated instances of it
>> with
>> > an
>> > > > > index
>> > > > > > >> > > > reference
>> > > > > > >> > > > > to
>> > > > > > >> > > > > > > the full string?
>> > > > > > >> > > > > >
>> > > > > > >> > > > > >
>> > > > > > >> > > > > > Hey James, yeah, that's probably true, but keep in
>> > mind
>> > > > that
>> > > > > > the
>> > > > > > >> > > > > > compression happens on the broker side. It would be
>> > nice
>> > > > to
>> > > > > > >> have a
>> > > > > > >> > > more
>> > > > > > >> > > > > > compact representation so that get some benefit
>> over
>> > the
>> > > > > wire
>> > > > > > as
>> > > > > > >> > > well.
>> > > > > > >> > > > > This
>> > > > > > >> > > > > > seems to be less of a concern here, so the bigger
>> > gains
>> > > > are
>> > > > > > >> > probably
>> > > > > > >> > > > from
>> > > > > > >> > > > > > reducing the number of partitions that need to be
>> > listed
>> > > > > > >> > > individually.
>> > > > > > >> > > > > >
>> > > > > > >> > > > > > -Jason
>> > > > > > >> > > > > >
>> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur Karaman <
>> > > > > > >> > > > > > onurkaraman.apache@gmail.com>
>> > > > > > >> > > > > > wrote:
>> > > > > > >> > > > > >
>> > > > > > >> > > > > > > When figuring out these optimizations, it's worth
>> > > > keeping
>> > > > > in
>> > > > > > >> mind
>> > > > > > >> > > the
>> > > > > > >> > > > > > > improvements when the message is uncompressed vs
>> > when
>> > > > it's
>> > > > > > >> > > > compressed.
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > When uncompressed:
>> > > > > > >> > > > > > > Fixing the Assignment serialization to instead
>> be a
>> > > > topic
>> > > > > > >> index
>> > > > > > >> > > into
>> > > > > > >> > > > > the
>> > > > > > >> > > > > > > corresponding member's subscription list would
>> > usually
>> > > > be
>> > > > > a
>> > > > > > >> good
>> > > > > > >> > > > thing.
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > I think the proposal is only worse when the topic
>> > > names
>> > > > > are
>> > > > > > >> > small.
>> > > > > > >> > > > The
>> > > > > > >> > > > > > > Type.STRING we use in our protocol for the
>> > > assignment's
>> > > > > > >> > > > TOPIC_KEY_NAME
>> > > > > > >> > > > > is
>> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so our
>> strings
>> > > are
>> > > > > > first
>> > > > > > >> > > > > prepended
>> > > > > > >> > > > > > > with 2 bytes to indicate the string size.
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > The new proposal does worse when:
>> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size <
>> > index_type_size
>> > > > > > >> > > > > > > in other words when:
>> > > > > > >> > > > > > > utf_encoded_string_payload_size <
>> index_type_size -
>> > 2
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > If the index type ends up being Type.INT32, then
>> the
>> > > > > > proposal
>> > > > > > >> is
>> > > > > > >> > > > worse
>> > > > > > >> > > > > > when
>> > > > > > >> > > > > > > the topic is length 1.
>> > > > > > >> > > > > > > If the index type ends up being Type.INT64, then
>> the
>> > > > > > proposal
>> > > > > > >> is
>> > > > > > >> > > > worse
>> > > > > > >> > > > > > when
>> > > > > > >> > > > > > > the topic is less than length 6.
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > When compressed:
>> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how
>> things
>> > > > change
>> > > > > > when
>> > > > > > >> > > > > > compression
>> > > > > > >> > > > > > > comes into the picture. This would be worth
>> > > > investigating.
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James Cheng <
>> > > > > > >> > wushujames@gmail.com
>> > > > > > >> > > >
>> > > > > > >> > > > > > wrote:
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason
>> Gustafson <
>> > > > > > >> > > > jason@confluent.io>
>> > > > > > >> > > > > > > > wrote:
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay out the
>> > > > > assignment
>> > > > > > >> > without
>> > > > > > >> > > > > > needing
>> > > > > > >> > > > > > > > to
>> > > > > > >> > > > > > > > > explicitly repeat the topic? For example, the
>> > > leader
>> > > > > > could
>> > > > > > >> > sort
>> > > > > > >> > > > the
>> > > > > > >> > > > > > > > topics
>> > > > > > >> > > > > > > > > for each member and just use an integer to
>> > > represent
>> > > > > the
>> > > > > > >> > index
>> > > > > > >> > > of
>> > > > > > >> > > > > > each
>> > > > > > >> > > > > > > > > topic within the sorted list (note this
>> depends
>> > on
>> > > > the
>> > > > > > >> > > > subscription
>> > > > > > >> > > > > > > > > including the full topic list).
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]]
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > > > Jason, doesn't gzip (or other compression)
>> > basically
>> > > > do
>> > > > > > >> this?
>> > > > > > >> > If
>> > > > > > >> > > > the
>> > > > > > >> > > > > > > topic
>> > > > > > >> > > > > > > > is a string and the topic is repeated
>> throughout,
>> > > > won't
>> > > > > > >> > > compression
>> > > > > > >> > > > > > > > basically replace all repeated instances of it
>> > with
>> > > an
>> > > > > > index
>> > > > > > >> > > > > reference
>> > > > > > >> > > > > > to
>> > > > > > >> > > > > > > > the full string?
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > > > -James
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > > > > You could even combine these two options so
>> that
>> > > you
>> > > > > > have
>> > > > > > >> > only
>> > > > > > >> > > 3
>> > > > > > >> > > > > > > integers
>> > > > > > >> > > > > > > > > for each topic assignment:
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition
>> > > MaxPartition]
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > There may even be better options with a
>> little
>> > > more
>> > > > > > >> thought.
>> > > > > > >> > > All
>> > > > > > >> > > > of
>> > > > > > >> > > > > > > this
>> > > > > > >> > > > > > > > is
>> > > > > > >> > > > > > > > > just part of the client-side protocol, so it
>> > > > wouldn't
>> > > > > > >> require
>> > > > > > >> > > any
>> > > > > > >> > > > > > > version
>> > > > > > >> > > > > > > > > bumps on the broker. What do you think?
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > Thanks,
>> > > > > > >> > > > > > > > > Jason
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM, Guozhang
>> Wang <
>> > > > > > >> > > > wangguoz@gmail.com
>> > > > > > >> > > > > >
>> > > > > > >> > > > > > > > wrote:
>> > > > > > >> > > > > > > > >
>> > > > > > >> > > > > > > > >> The original concern is that regex may not
>> be
>> > > > > > efficiently
>> > > > > > >> > > > > supported
>> > > > > > >> > > > > > > > >> across-languages, but if there is a neat
>> > > > workaround I
>> > > > > > >> would
>> > > > > > >> > > love
>> > > > > > >> > > > > to
>> > > > > > >> > > > > > > > learn.
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >> Guozhang
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM, Ismael
>> Juma <
>> > > > > > >> > > ismael@juma.me.uk
>> > > > > > >> > > > >
>> > > > > > >> > > > > > > wrote:
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion.
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>> Having said that, as a general point, I
>> think
>> > we
>> > > > > > should
>> > > > > > >> > > > consider
>> > > > > > >> > > > > > > > >> supporting
>> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol. It
>> > requires
>> > > > > some
>> > > > > > >> > > thinking
>> > > > > > >> > > > > for
>> > > > > > >> > > > > > > > >>> cross-language support, but it seems
>> > > surmountable
>> > > > > and
>> > > > > > it
>> > > > > > >> > > could
>> > > > > > >> > > > > make
>> > > > > > >> > > > > > > > >> certain
>> > > > > > >> > > > > > > > >>> operations a lot more efficient (the fact
>> > that a
>> > > > > basic
>> > > > > > >> > regex
>> > > > > > >> > > > > > > > subscription
>> > > > > > >> > > > > > > > >>> causes the consumer to request metadata for
>> > all
>> > > > > topics
>> > > > > > >> is
>> > > > > > >> > not
>> > > > > > >> > > > > > great).
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>> Ismael
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM, Guozhang
>> > Wang
>> > > <
>> > > > > > >> > > > > > wangguoz@gmail.com>
>> > > > > > >> > > > > > > > >>> wrote:
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing the
>> > > handling
>> > > > > > >> logics of
>> > > > > > >> > > > > single
>> > > > > > >> > > > > > > > large
>> > > > > > >> > > > > > > > >>>> message on the consumer side.
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>> As for the case of "a single group
>> > subscribing
>> > > to
>> > > > > > 3000
>> > > > > > >> > > > topics",
>> > > > > > >> > > > > > with
>> > > > > > >> > > > > > > > >> 100
>> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is
>> reasonable
>> > to
>> > > me
>> > > > > > (when
>> > > > > > >> > > > storing
>> > > > > > >> > > > > in
>> > > > > > >> > > > > > > ZK,
>> > > > > > >> > > > > > > > >> we
>> > > > > > >> > > > > > > > >>>> also have the znode limit which is set to
>> 1Mb
>> > > by
>> > > > > > >> default,
>> > > > > > >> > > > though
>> > > > > > >> > > > > > > > >>> admittedly
>> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if we do
>> > the
>> > > > > change
>> > > > > > >> as
>> > > > > > >> > Jun
>> > > > > > >> > > > > > > > suggested,
>> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure is OK
>> I
>> > > > think.
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>> Guozhang
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM, Onur
>> > Karaman
>> > > <
>> > > > > > >> > > > > > > > >>>> onurkaraman.apache@gmail.com
>> > > > > > >> > > > > > > > >>>>> wrote:
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>>> Results without compression:
>> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes
>> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the tipping
>> > point
>> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes
>> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes
>> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes
>> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes
>> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes
>> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes
>> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes
>> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes
>> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes
>> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes
>> > > > > > >> > > > > > > > >>>>>
>> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression shrinks
>> > the
>> > > > > > message
>> > > > > > >> > size
>> > > > > > >> > > by
>> > > > > > >> > > > > 4x.
>> > > > > > >> > > > > > > > >>>>>
>> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM, Jun Rao
>> <
>> > > > > > >> > jun@confluent.io
>> > > > > > >> > > >
>> > > > > > >> > > > > > wrote:
>> > > > > > >> > > > > > > > >>>>>
>> > > > > > >> > > > > > > > >>>>>> Onur,
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation.
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how we
>> deal
>> > > with
>> > > > > the
>> > > > > > >> case
>> > > > > > >> > > > when a
>> > > > > > >> > > > > > > > >>> message
>> > > > > > >> > > > > > > > >>>> is
>> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today, if
>> the
>> > > fetch
>> > > > > > size
>> > > > > > >> is
>> > > > > > >> > > > > smaller
>> > > > > > >> > > > > > > > >> than
>> > > > > > >> > > > > > > > >>>> the
>> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get stuck.
>> > > > Instead,
>> > > > > > we
>> > > > > > >> can
>> > > > > > >> > > > > simply
>> > > > > > >> > > > > > > > >>> return
>> > > > > > >> > > > > > > > >>>>> the
>> > > > > > >> > > > > > > > >>>>>> full message if it's larger than the
>> fetch
>> > > size
>> > > > > w/o
>> > > > > > >> > > > requiring
>> > > > > > >> > > > > > the
>> > > > > > >> > > > > > > > >>>>> consumer
>> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size. On
>> the
>> > > > broker
>> > > > > > >> side,
>> > > > > > >> > to
>> > > > > > >> > > > > serve
>> > > > > > >> > > > > > a
>> > > > > > >> > > > > > > > >>> fetch
>> > > > > > >> > > > > > > > >>>>>> request, we already do an index lookup
>> and
>> > > then
>> > > > > > scan
>> > > > > > >> the
>> > > > > > >> > > > log a
>> > > > > > >> > > > > > bit
>> > > > > > >> > > > > > > > >> to
>> > > > > > >> > > > > > > > >>>>> find
>> > > > > > >> > > > > > > > >>>>>> the message with the requested offset.
>> We
>> > can
>> > > > > just
>> > > > > > >> check
>> > > > > > >> > > the
>> > > > > > >> > > > > > size
>> > > > > > >> > > > > > > > >> of
>> > > > > > >> > > > > > > > >>>> that
>> > > > > > >> > > > > > > > >>>>>> message and return the full message if
>> its
>> > > size
>> > > > > is
>> > > > > > >> > larger
>> > > > > > >> > > > than
>> > > > > > >> > > > > > the
>> > > > > > >> > > > > > > > >>>> fetch
>> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is really for
>> > > > > > performance
>> > > > > > >> > > > > > optimization,
>> > > > > > >> > > > > > > > >>> i.e.
>> > > > > > >> > > > > > > > >>>>> in
>> > > > > > >> > > > > > > > >>>>>> the common case, we will not return more
>> > > bytes
>> > > > > than
>> > > > > > >> > fetch
>> > > > > > >> > > > > size,
>> > > > > > >> > > > > > > but
>> > > > > > >> > > > > > > > >>> if
>> > > > > > >> > > > > > > > >>>>>> there is a large message, we will return
>> > more
>> > > > > bytes
>> > > > > > >> than
>> > > > > > >> > > the
>> > > > > > >> > > > > > > > >>> specified
>> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large messages
>> are
>> > > > rare.
>> > > > > > >> So, it
>> > > > > > >> > > > > > shouldn't
>> > > > > > >> > > > > > > > >>>>> increase
>> > > > > > >> > > > > > > > >>>>>> the memory consumption on the client too
>> > > much.
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>> Jun
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM, Onur
>> > > Karaman <
>> > > > > > >> > > > > > > > >>>>>> onurkaraman.apache@gmail.com>
>> > > > > > >> > > > > > > > >>>>>> wrote:
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing some
>> > tests
>> > > on
>> > > > > the
>> > > > > > >> new
>> > > > > > >> > > > > > > > >>>>>> consumer/coordinator
>> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more
>> strenuous
>> > use
>> > > > > cases
>> > > > > > >> like
>> > > > > > >> > > > > > mirroring
>> > > > > > >> > > > > > > > >>>>>> clusters
>> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and thought
>> I'd
>> > > share
>> > > > > > >> > whatever I
>> > > > > > >> > > > > have
>> > > > > > >> > > > > > so
>> > > > > > >> > > > > > > > >>>> far.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount of
>> group
>> > > > > > metadata
>> > > > > > >> we
>> > > > > > >> > > can
>> > > > > > >> > > > > fit
>> > > > > > >> > > > > > > > >> into
>> > > > > > >> > > > > > > > >>>> one
>> > > > > > >> > > > > > > > >>>>>>> message
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Some background:
>> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is implemented
>> in
>> > two
>> > > > > > phases
>> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase that
>> > > identifies
>> > > > > > >> members
>> > > > > > >> > of
>> > > > > > >> > > > the
>> > > > > > >> > > > > > > > >> group
>> > > > > > >> > > > > > > > >>>> and
>> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions.
>> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that waits for
>> > the
>> > > > > group
>> > > > > > >> > leader
>> > > > > > >> > > to
>> > > > > > >> > > > > > > > >> decide
>> > > > > > >> > > > > > > > >>>>> member
>> > > > > > >> > > > > > > > >>>>>>> assignments based on the member
>> > > subscriptions
>> > > > > > across
>> > > > > > >> > the
>> > > > > > >> > > > > group.
>> > > > > > >> > > > > > > > >>>>>>>  - The leader announces this decision
>> > with a
>> > > > > > >> > > > > SyncGroupRequest.
>> > > > > > >> > > > > > > > >> The
>> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles
>> SyncGroupRequests
>> > > by
>> > > > > > >> appending
>> > > > > > >> > > all
>> > > > > > >> > > > > > group
>> > > > > > >> > > > > > > > >>>> state
>> > > > > > >> > > > > > > > >>>>>>> into a single message under the
>> > > > > __consumer_offsets
>> > > > > > >> > topic.
>> > > > > > >> > > > > This
>> > > > > > >> > > > > > > > >>>> message
>> > > > > > >> > > > > > > > >>>>> is
>> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and contains each
>> > > member
>> > > > > > >> > > subscription
>> > > > > > >> > > > > as
>> > > > > > >> > > > > > > > >> well
>> > > > > > >> > > > > > > > >>>> as
>> > > > > > >> > > > > > > > >>>>>> the
>> > > > > > >> > > > > > > > >>>>>>> decided assignment for each member.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> The environment:
>> > > > > > >> > > > > > > > >>>>>>> - one broker
>> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets partition
>> > > > > > >> > > > > > > > >>>>>>> - offsets.topic.compression.codec=1 //
>> > this
>> > > is
>> > > > > > gzip
>> > > > > > >> > > > > > > > >>>>>>> - broker has my pending KAFKA-3718
>> patch
>> > > that
>> > > > > > >> actually
>> > > > > > >> > > > makes
>> > > > > > >> > > > > > use
>> > > > > > >> > > > > > > > >> of
>> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec:
>> > > > > > >> > > > > > > > >>>>>>
>> https://github.com/apache/kafka/pull/1394
>> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an actual
>> > > subset
>> > > > > of
>> > > > > > >> > topics
>> > > > > > >> > > > from
>> > > > > > >> > > > > > one
>> > > > > > >> > > > > > > > >>> of
>> > > > > > >> > > > > > > > >>>>> our
>> > > > > > >> > > > > > > > >>>>>>> clusters.
>> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions
>> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long on
>> average
>> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number of
>> > > consumers
>> > > > > > each
>> > > > > > >> > > > hardcoded
>> > > > > > >> > > > > > > > >> with
>> > > > > > >> > > > > > > > >>>> all
>> > > > > > >> > > > > > > > >>>>>> the
>> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests more
>> > > consistent.
>> > > > > > >> > > wildcarding
>> > > > > > >> > > > > with
>> > > > > > >> > > > > > > > >> .*
>> > > > > > >> > > > > > > > >>>>> should
>> > > > > > >> > > > > > > > >>>>>>> have the same effect once the
>> subscription
>> > > > hits
>> > > > > > the
>> > > > > > >> > > > > coordinator
>> > > > > > >> > > > > > > > >> as
>> > > > > > >> > > > > > > > >>>> the
>> > > > > > >> > > > > > > > >>>>>>> subscription has already been fully
>> > expanded
>> > > > out
>> > > > > > to
>> > > > > > >> the
>> > > > > > >> > > > list
>> > > > > > >> > > > > of
>> > > > > > >> > > > > > > > >>>> topics
>> > > > > > >> > > > > > > > >>>>> by
>> > > > > > >> > > > > > > > >>>>>>> the consumers.
>> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to
>> Log.scala
>> > to
>> > > > > print
>> > > > > > >> out
>> > > > > > >> > the
>> > > > > > >> > > > > > message
>> > > > > > >> > > > > > > > >>>> sizes
>> > > > > > >> > > > > > > > >>>>>>> after compression
>> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all and
>> auto
>> > > > commits
>> > > > > > are
>> > > > > > >> > > > > disabled.
>> > > > > > >> > > > > > > > >> The
>> > > > > > >> > > > > > > > >>>> only
>> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added is
>> the
>> > > > > > >> > > __consumer_offsets
>> > > > > > >> > > > > > topic
>> > > > > > >> > > > > > > > >>> and
>> > > > > > >> > > > > > > > >>>>>>> they're only from storing group
>> metadata
>> > > while
>> > > > > > >> > processing
>> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Results:
>> > > > > > >> > > > > > > > >>>>>>> The results below show that we exceed
>> the
>> > > > > 1000012
>> > > > > > >> byte
>> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit
>> > relatively
>> > > > > > quickly
>> > > > > > >> > > > (between
>> > > > > > >> > > > > > > > >> 30-40
>> > > > > > >> > > > > > > > >>>>>>> consumers):
>> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes
>> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes
>> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes
>> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes
>> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes
>> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the
>> tipping
>> > > point
>> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes
>> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes
>> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes
>> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes
>> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes
>> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is pretty
>> > > gradual.
>> > > > > > >> Plotting
>> > > > > > >> > > the
>> > > > > > >> > > > > > > > >> points
>> > > > > > >> > > > > > > > >>>>> makes
>> > > > > > >> > > > > > > > >>>>>> it
>> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the number of
>> > > > > consumers:
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > >
>> > > > > > >> > > > >
>> > > > > > >> > > >
>> > > > > > >> > >
>> > > > > > >> >
>> > > > > > >>
>> > > > > >
>> > > > >
>> > > >
>> > >
>> >
>> https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735)
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers aren't
>> > averages
>> > > > or
>> > > > > > >> medians
>> > > > > > >> > > or
>> > > > > > >> > > > > > > > >> anything
>> > > > > > >> > > > > > > > >>>>> like
>> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size from a
>> given
>> > > > run.
>> > > > > I
>> > > > > > >> did
>> > > > > > >> > run
>> > > > > > >> > > > > them
>> > > > > > >> > > > > > a
>> > > > > > >> > > > > > > > >>> few
>> > > > > > >> > > > > > > > >>>>>> times
>> > > > > > >> > > > > > > > >>>>>>> and saw similar results.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Impact:
>> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the
>> > > > __consumer_offsets
>> > > > > > >> topic
>> > > > > > >> > > with
>> > > > > > >> > > > > my
>> > > > > > >> > > > > > > > >>>> pending
>> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the AwaitingSync
>> phase
>> > of
>> > > > the
>> > > > > > >> group
>> > > > > > >> > > fails
>> > > > > > >> > > > > > with
>> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This means the
>> > > > combined
>> > > > > > >> size
>> > > > > > >> > of
>> > > > > > >> > > > each
>> > > > > > >> > > > > > > > >>>> member's
>> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments exceeded
>> the
>> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes
>> > > > > > >> > > > > > > > >>>>> of
>> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up dying.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Options:
>> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the number of
>> > > > consumers
>> > > > > > in
>> > > > > > >> the
>> > > > > > >> > > > > group.
>> > > > > > >> > > > > > > > >> This
>> > > > > > >> > > > > > > > >>>>> isn't
>> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more
>> > strenuous
>> > > > use
>> > > > > > >> cases
>> > > > > > >> > > like
>> > > > > > >> > > > > > > > >>>> MirrorMaker
>> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing.
>> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group into
>> > > smaller
>> > > > > > >> groups
>> > > > > > >> > > which
>> > > > > > >> > > > > > > > >>> together
>> > > > > > >> > > > > > > > >>>>> will
>> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics. This
>> > gives
>> > > > each
>> > > > > > >> group
>> > > > > > >> > > > > member a
>> > > > > > >> > > > > > > > >>>> smaller
>> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics
>> starting
>> > > with
>> > > > > a-m
>> > > > > > >> while
>> > > > > > >> > > g2
>> > > > > > >> > > > > has
>> > > > > > >> > > > > > > > >>> topics
>> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be
>> > > operationally
>> > > > > > >> painful
>> > > > > > >> > to
>> > > > > > >> > > > > > manage.
>> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the topics
>> among
>> > > > members
>> > > > > > of
>> > > > > > >> the
>> > > > > > >> > > > > group.
>> > > > > > >> > > > > > > > >>> Again
>> > > > > > >> > > > > > > > >>>>> this
>> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller
>> > > > subscription.
>> > > > > > This
>> > > > > > >> > > would
>> > > > > > >> > > > > also
>> > > > > > >> > > > > > > > >> be
>> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage.
>> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up
>> > > > > > >> KafkaConfig.messageMaxBytes
>> > > > > > >> > (a
>> > > > > > >> > > > > > > > >>> topic-level
>> > > > > > >> > > > > > > > >>>>>>> config) and
>> > KafkaConfig.replicaFetchMaxBytes
>> > > > (a
>> > > > > > >> > > > broker-level
>> > > > > > >> > > > > > > > >>> config).
>> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just the
>> > > > > > >> __consumer_offsets
>> > > > > > >> > > > topic
>> > > > > > >> > > > > > > > >> seems
>> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping up the
>> > > > > > broker-level
>> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes
>> > > > > > >> > > > > > > > >>>>>>> would probably need more attention.
>> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different
>> > compression
>> > > > > > codecs.
>> > > > > > >> > Based
>> > > > > > >> > > > on
>> > > > > > >> > > > > 2
>> > > > > > >> > > > > > > > >>>> minutes
>> > > > > > >> > > > > > > > >>>>> of
>> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and snappy
>> are
>> > > > > faster
>> > > > > > >> than
>> > > > > > >> > > gzip
>> > > > > > >> > > > > but
>> > > > > > >> > > > > > > > >>> have
>> > > > > > >> > > > > > > > >>>>>> worse
>> > > > > > >> > > > > > > > >>>>>>> compression, so this probably won't
>> help.
>> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support
>> sending
>> > > the
>> > > > > > regex
>> > > > > > >> > over
>> > > > > > >> > > > the
>> > > > > > >> > > > > > wire
>> > > > > > >> > > > > > > > >>>>> instead
>> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic
>> > subscriptions. I
>> > > > > think
>> > > > > > >> > people
>> > > > > > >> > > > > said
>> > > > > > >> > > > > > in
>> > > > > > >> > > > > > > > >>> the
>> > > > > > >> > > > > > > > >>>>>> past
>> > > > > > >> > > > > > > > >>>>>>> that different languages have subtle
>> > > > differences
>> > > > > > in
>> > > > > > >> > > regex,
>> > > > > > >> > > > so
>> > > > > > >> > > > > > > > >> this
>> > > > > > >> > > > > > > > >>>>>> doesn't
>> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language groups.
>> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe we can
>> > > reverse
>> > > > > the
>> > > > > > >> > > mapping?
>> > > > > > >> > > > > > > > >> Instead
>> > > > > > >> > > > > > > > >>>> of
>> > > > > > >> > > > > > > > >>>>>>> mapping from member to subscriptions,
>> we
>> > can
>> > > > > map a
>> > > > > > >> > > > > subscription
>> > > > > > >> > > > > > > > >> to
>> > > > > > >> > > > > > > > >>> a
>> > > > > > >> > > > > > > > >>>>> list
>> > > > > > >> > > > > > > > >>>>>>> of members.
>> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe we can
>> try
>> > > to
>> > > > > > break
>> > > > > > >> > apart
>> > > > > > >> > > > the
>> > > > > > >> > > > > > > > >>>>>> subscription
>> > > > > > >> > > > > > > > >>>>>>> and assignments from the same
>> > > SyncGroupRequest
>> > > > > > into
>> > > > > > >> > > > multiple
>> > > > > > >> > > > > > > > >>> records?
>> > > > > > >> > > > > > > > >>>>>> They
>> > > > > > >> > > > > > > > >>>>>>> can still go to the same message set
>> and
>> > get
>> > > > > > >> appended
>> > > > > > >> > > > > together.
>> > > > > > >> > > > > > > > >>> This
>> > > > > > >> > > > > > > > >>>>> way
>> > > > > > >> > > > > > > > >>>>>>> the limit become the segment size,
>> which
>> > > > > shouldn't
>> > > > > > >> be a
>> > > > > > >> > > > > > problem.
>> > > > > > >> > > > > > > > >>> This
>> > > > > > >> > > > > > > > >>>>> can
>> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because we're
>> > > currently
>> > > > > > >> keying
>> > > > > > >> > > these
>> > > > > > >> > > > > > > > >>> messages
>> > > > > > >> > > > > > > > >>>> on
>> > > > > > >> > > > > > > > >>>>>> the
>> > > > > > >> > > > > > > > >>>>>>> group, so I think records from the same
>> > > > > rebalance
>> > > > > > >> might
>> > > > > > >> > > > > > > > >>> accidentally
>> > > > > > >> > > > > > > > >>>>>>> compact one another, but my
>> understanding
>> > of
>> > > > > > >> compaction
>> > > > > > >> > > > isn't
>> > > > > > >> > > > > > > > >> that
>> > > > > > >> > > > > > > > >>>>> great.
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> Todo:
>> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun the
>> tests
>> > > > with
>> > > > > no
>> > > > > > >> > > > > compression
>> > > > > > >> > > > > > > > >> just
>> > > > > > >> > > > > > > > >>>> to
>> > > > > > >> > > > > > > > >>>>>> see
>> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's
>> getting
>> > > > late.
>> > > > > > >> Maybe
>> > > > > > >> > > > > tomorrow?
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>> - Onur
>> > > > > > >> > > > > > > > >>>>>>>
>> > > > > > >> > > > > > > > >>>>>>
>> > > > > > >> > > > > > > > >>>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>> --
>> > > > > > >> > > > > > > > >>>> -- Guozhang
>> > > > > > >> > > > > > > > >>>>
>> > > > > > >> > > > > > > > >>>
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > > >> --
>> > > > > > >> > > > > > > > >> -- Guozhang
>> > > > > > >> > > > > > > > >>
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > > >
>> > > > > > >> > > > > > >
>> > > > > > >> > > > > >
>> > > > > > >> > > > >
>> > > > > > >> > > >
>> > > > > > >> > >
>> > > > > > >> >
>> > > > > > >> >
>> > > > > > >> >
>> > > > > > >> > --
>> > > > > > >> > -- Guozhang
>> > > > > > >> >
>> > > > > > >>
>> > > > > > >
>> > > > > > >
>> > > > > >
>> > > > >
>> > > >
>> > >
>> >
>>
>
>