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Posted to user@cassandra.apache.org by Stefano Ortolani <os...@gmail.com> on 2017/05/16 13:33:50 UTC
Range deletes, wide partitions, and reverse iterators
Hi all,
I am seeing inconsistencies when mixing range tombstones, wide partitions,
and reverse iterators.
I still have to understand if the behaviour is to be expected hence the
message on the mailing list.
The situation is conceptually simple. I am using a table defined as follows:
CREATE TABLE test_cql.test_cf (
hash blob,
timeid timeuuid,
PRIMARY KEY (hash, timeid)
) WITH CLUSTERING ORDER BY (timeid ASC)
AND compaction = {'class' : 'LeveledCompactionStrategy'};
I then proceed by loading 2/3GB from 3 sstables which I know contain a
really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
_half_ of that partition by executing the query below, and restart the node:
DELETE
FROM test_cql.test_cf
WHERE hash = x AND timeid < y;
If I keep compactions disabled the following query timeouts (takes more
than 10 seconds to
succeed):
SELECT *
FROM test_cql.test_cf
WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
ORDER BY timeid ASC;
While the following returns immediately (obviously because no deleted data
is ever read):
SELECT *
FROM test_cql.test_cf
WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
ORDER BY timeid DESC;
If I force a compaction the problem is gone, but I presume just because the
data is rearranged.
It seems to me that reading by ASC does not make use of the range tombstone
until C* reads the
last sstables (which actually contains the range tombstone and is flushed
at node restart), and it wastes time reading all rows that are actually not
live anymore.
Is this expected? Should the range tombstone actually help in these cases?
Thanks a lot!
Stefano
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
Yes, I agree. I would say it cannot skip those cells because it doesn’t check the max timestamp of the cells of the sstable and therefore scans them one by one.
Hannu
> On 16 May 2017, at 19:48, Stefano Ortolani <os...@gmail.com> wrote:
>
> But it should skip those records since they are sorted. My understanding would be something like:
>
> 1) read sstable 2
> 2) read the range tombstone
> 3) skip records from sstable2 and sstable1 within the range boundaries
> 4) read remaining records from sstable1
> 5) no records, return
>
> On Tue, May 16, 2017 at 5:43 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
> This is a bit of guessing but it probably reads sstables in some sort of sequence, so even if sstable 2 contains the tombstone, it still scans through the sstable 1 for possible data to be read.
>
> BR,
> Hannu
>
>> On 16 May 2017, at 19:40, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>
>> Little update: also the following query timeouts, which is weird since the range tombstone should have been read by then...
>>
>> SELECT *
>> FROM test_cql.test_cf
>> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> AND timeid < the_oldest_deleted_timeid
>> ORDER BY timeid DESC;
>>
>>
>>
>> On Tue, May 16, 2017 at 5:17 PM, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>> Yes, that was my intention but I wanted to cross-check with the ML and the devs keeping an eye on it first.
>>
>> On Tue, May 16, 2017 at 5:10 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>> Well,
>>
>> sstables contain some statistics about the cell timestamps and using that information and the tombstone timestamp it might be possible to skip some data but I’m not sure that Cassandra currently does that. Maybe it would be worth a JIRA ticket and see what the devs think about it. If optimizing this case would make sense.
>>
>> Hannu
>>
>>> On 16 May 2017, at 18:03, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>>
>>> Hi Hannu,
>>>
>>> the piece of data in question is older. In my example the tombstone is the newest piece of data.
>>> Since a range tombstone has information re the clustering key ranges, and the data is clustering key sorted, I would expect a linear scan not to be necessary.
>>>
>>> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>>> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
>>>
>>> Hannu
>>>
>>>> On 16 May 2017, at 17:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>>>
>>>> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
>>>> That is why I am puzzled by this afore-mentioned behavior.
>>>> I would expect them to handle this case more gracefully.
>>>>
>>>> Cheers,
>>>> Stefano
>>>>
>>>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
>>>> Hannu,
>>>>
>>>> How can you read a partition in reverse?
>>>>
>>>> Sent from my iPhone
>>>>
>>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>>>> >
>>>> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>>>> >
>>>> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>>>> >
>>>> > Does it make sense?
>>>> >
>>>> > Hannu
>>>> >
>>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>>> >>
>>>> >> Hi all,
>>>> >>
>>>> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>>>> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>>>> >>
>>>> >> The situation is conceptually simple. I am using a table defined as follows:
>>>> >>
>>>> >> CREATE TABLE test_cql.test_cf (
>>>> >> hash blob,
>>>> >> timeid timeuuid,
>>>> >> PRIMARY KEY (hash, timeid)
>>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>>> >>
>>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>>>> >>
>>>> >> DELETE
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = x AND timeid < y;
>>>> >>
>>>> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>>>> >> succeed):
>>>> >>
>>>> >> SELECT *
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>> >> ORDER BY timeid ASC;
>>>> >>
>>>> >> While the following returns immediately (obviously because no deleted data is ever read):
>>>> >>
>>>> >> SELECT *
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>> >> ORDER BY timeid DESC;
>>>> >>
>>>> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>>>> >>
>>>> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>>>> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>>>> >>
>>>> >> Is this expected? Should the range tombstone actually help in these cases?
>>>> >>
>>>> >> Thanks a lot!
>>>> >> Stefano
>>>> >
>>>> >
>>>> > ---------------------------------------------------------------------
>>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
>>>> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
>>>> >
>>>>
>>>
>>>
>>
>>
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
But it should skip those records since they are sorted. My understanding
would be something like:
1) read sstable 2
2) read the range tombstone
3) skip records from sstable2 and sstable1 within the range boundaries
4) read remaining records from sstable1
5) no records, return
On Tue, May 16, 2017 at 5:43 PM, Hannu Kröger <hk...@gmail.com> wrote:
> This is a bit of guessing but it probably reads sstables in some sort of
> sequence, so even if sstable 2 contains the tombstone, it still scans
> through the sstable 1 for possible data to be read.
>
> BR,
> Hannu
>
> On 16 May 2017, at 19:40, Stefano Ortolani <os...@gmail.com> wrote:
>
> Little update: also the following query timeouts, which is weird since the
> range tombstone should have been read by then...
>
> SELECT *
> FROM test_cql.test_cf
> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> AND timeid < the_oldest_deleted_timeid
> ORDER BY timeid DESC;
>
>
>
> On Tue, May 16, 2017 at 5:17 PM, Stefano Ortolani <os...@gmail.com>
> wrote:
>
>> Yes, that was my intention but I wanted to cross-check with the ML and
>> the devs keeping an eye on it first.
>>
>> On Tue, May 16, 2017 at 5:10 PM, Hannu Kröger <hk...@gmail.com> wrote:
>>
>>> Well,
>>>
>>> sstables contain some statistics about the cell timestamps and using
>>> that information and the tombstone timestamp it might be possible to skip
>>> some data but I’m not sure that Cassandra currently does that. Maybe it
>>> would be worth a JIRA ticket and see what the devs think about it. If
>>> optimizing this case would make sense.
>>>
>>> Hannu
>>>
>>> On 16 May 2017, at 18:03, Stefano Ortolani <os...@gmail.com> wrote:
>>>
>>> Hi Hannu,
>>>
>>> the piece of data in question is older. In my example the tombstone is
>>> the newest piece of data.
>>> Since a range tombstone has information re the clustering key ranges,
>>> and the data is clustering key sorted, I would expect a linear scan not to
>>> be necessary.
>>>
>>> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hk...@gmail.com> wrote:
>>>
>>>> Well, as mentioned, probably Cassandra doesn’t have logic and data to
>>>> skip bigger regions of deleted data based on range tombstone. If some piece
>>>> of data in a partition is newer than the tombstone, then it cannot be
>>>> skipped. Therefore some partition level statistics of cell ages would need
>>>> to be kept in the column index for the skipping and that is probably not
>>>> there.
>>>>
>>>> Hannu
>>>>
>>>> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>>>>
>>>> That is another way to see the question: are reverse iterators range
>>>> tombstone aware? Yes.
>>>> That is why I am puzzled by this afore-mentioned behavior.
>>>> I would expect them to handle this case more gracefully.
>>>>
>>>> Cheers,
>>>> Stefano
>>>>
>>>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com>
>>>> wrote:
>>>>
>>>>> Hannu,
>>>>>
>>>>> How can you read a partition in reverse?
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>>>>> >
>>>>> > Well, I’m guessing that Cassandra doesn't really know if the range
>>>>> tombstone is useful for this or not.
>>>>> >
>>>>> > In many cases it might be that the partition contains data that is
>>>>> within the range of the tombstone but is newer than the tombstone and
>>>>> therefore it might be still be returned. Scanning through deleted data can
>>>>> be avoided by reading the partition in reverse (if all the deleted data is
>>>>> in the beginning of the partition). Eventually you will still end up
>>>>> reading a lot of tombstones but you will get a lot of live data first and
>>>>> the implicit query limit of 10000 probably is reached before you get to the
>>>>> tombstones. Therefore you will get an immediate answer.
>>>>> >
>>>>> > Does it make sense?
>>>>> >
>>>>> > Hannu
>>>>> >
>>>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com>
>>>>> wrote:
>>>>> >>
>>>>> >> Hi all,
>>>>> >>
>>>>> >> I am seeing inconsistencies when mixing range tombstones, wide
>>>>> partitions, and reverse iterators.
>>>>> >> I still have to understand if the behaviour is to be expected hence
>>>>> the message on the mailing list.
>>>>> >>
>>>>> >> The situation is conceptually simple. I am using a table defined as
>>>>> follows:
>>>>> >>
>>>>> >> CREATE TABLE test_cql.test_cf (
>>>>> >> hash blob,
>>>>> >> timeid timeuuid,
>>>>> >> PRIMARY KEY (hash, timeid)
>>>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>>>> >>
>>>>> >> I then proceed by loading 2/3GB from 3 sstables which I know
>>>>> contain a really wide partition (> 512 MB) for `hash = x`. I then delete
>>>>> the oldest _half_ of that partition by executing the query below, and
>>>>> restart the node:
>>>>> >>
>>>>> >> DELETE
>>>>> >> FROM test_cql.test_cf
>>>>> >> WHERE hash = x AND timeid < y;
>>>>> >>
>>>>> >> If I keep compactions disabled the following query timeouts (takes
>>>>> more than 10 seconds to
>>>>> >> succeed):
>>>>> >>
>>>>> >> SELECT *
>>>>> >> FROM test_cql.test_cf
>>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>>> >> ORDER BY timeid ASC;
>>>>> >>
>>>>> >> While the following returns immediately (obviously because no
>>>>> deleted data is ever read):
>>>>> >>
>>>>> >> SELECT *
>>>>> >> FROM test_cql.test_cf
>>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>>> >> ORDER BY timeid DESC;
>>>>> >>
>>>>> >> If I force a compaction the problem is gone, but I presume just
>>>>> because the data is rearranged.
>>>>> >>
>>>>> >> It seems to me that reading by ASC does not make use of the range
>>>>> tombstone until C* reads the
>>>>> >> last sstables (which actually contains the range tombstone and is
>>>>> flushed at node restart), and it wastes time reading all rows that are
>>>>> actually not live anymore.
>>>>> >>
>>>>> >> Is this expected? Should the range tombstone actually help in these
>>>>> cases?
>>>>> >>
>>>>> >> Thanks a lot!
>>>>> >> Stefano
>>>>> >
>>>>> >
>>>>> > ------------------------------------------------------------
>>>>> ---------
>>>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>>>>> > For additional commands, e-mail: user-help@cassandra.apache.org
>>>>> >
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
This is a bit of guessing but it probably reads sstables in some sort of sequence, so even if sstable 2 contains the tombstone, it still scans through the sstable 1 for possible data to be read.
BR,
Hannu
> On 16 May 2017, at 19:40, Stefano Ortolani <os...@gmail.com> wrote:
>
> Little update: also the following query timeouts, which is weird since the range tombstone should have been read by then...
>
> SELECT *
> FROM test_cql.test_cf
> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> AND timeid < the_oldest_deleted_timeid
> ORDER BY timeid DESC;
>
>
>
> On Tue, May 16, 2017 at 5:17 PM, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
> Yes, that was my intention but I wanted to cross-check with the ML and the devs keeping an eye on it first.
>
> On Tue, May 16, 2017 at 5:10 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
> Well,
>
> sstables contain some statistics about the cell timestamps and using that information and the tombstone timestamp it might be possible to skip some data but I’m not sure that Cassandra currently does that. Maybe it would be worth a JIRA ticket and see what the devs think about it. If optimizing this case would make sense.
>
> Hannu
>
>> On 16 May 2017, at 18:03, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>
>> Hi Hannu,
>>
>> the piece of data in question is older. In my example the tombstone is the newest piece of data.
>> Since a range tombstone has information re the clustering key ranges, and the data is clustering key sorted, I would expect a linear scan not to be necessary.
>>
>> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
>>
>> Hannu
>>
>>> On 16 May 2017, at 17:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>>
>>> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
>>> That is why I am puzzled by this afore-mentioned behavior.
>>> I would expect them to handle this case more gracefully.
>>>
>>> Cheers,
>>> Stefano
>>>
>>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
>>> Hannu,
>>>
>>> How can you read a partition in reverse?
>>>
>>> Sent from my iPhone
>>>
>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>>> >
>>> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>>> >
>>> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>>> >
>>> > Does it make sense?
>>> >
>>> > Hannu
>>> >
>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>> >>
>>> >> Hi all,
>>> >>
>>> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>>> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>>> >>
>>> >> The situation is conceptually simple. I am using a table defined as follows:
>>> >>
>>> >> CREATE TABLE test_cql.test_cf (
>>> >> hash blob,
>>> >> timeid timeuuid,
>>> >> PRIMARY KEY (hash, timeid)
>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>> >>
>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>>> >>
>>> >> DELETE
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = x AND timeid < y;
>>> >>
>>> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>>> >> succeed):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid ASC;
>>> >>
>>> >> While the following returns immediately (obviously because no deleted data is ever read):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid DESC;
>>> >>
>>> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>>> >>
>>> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>>> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>>> >>
>>> >> Is this expected? Should the range tombstone actually help in these cases?
>>> >>
>>> >> Thanks a lot!
>>> >> Stefano
>>> >
>>> >
>>> > ---------------------------------------------------------------------
>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
>>> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
>>> >
>>>
>>
>>
>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
Little update: also the following query timeouts, which is weird since the
range tombstone should have been read by then...
SELECT *
FROM test_cql.test_cf
WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
AND timeid < the_oldest_deleted_timeid
ORDER BY timeid DESC;
On Tue, May 16, 2017 at 5:17 PM, Stefano Ortolani <os...@gmail.com>
wrote:
> Yes, that was my intention but I wanted to cross-check with the ML and the
> devs keeping an eye on it first.
>
> On Tue, May 16, 2017 at 5:10 PM, Hannu Kröger <hk...@gmail.com> wrote:
>
>> Well,
>>
>> sstables contain some statistics about the cell timestamps and using that
>> information and the tombstone timestamp it might be possible to skip some
>> data but I’m not sure that Cassandra currently does that. Maybe it would be
>> worth a JIRA ticket and see what the devs think about it. If optimizing
>> this case would make sense.
>>
>> Hannu
>>
>> On 16 May 2017, at 18:03, Stefano Ortolani <os...@gmail.com> wrote:
>>
>> Hi Hannu,
>>
>> the piece of data in question is older. In my example the tombstone is
>> the newest piece of data.
>> Since a range tombstone has information re the clustering key ranges, and
>> the data is clustering key sorted, I would expect a linear scan not to be
>> necessary.
>>
>> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hk...@gmail.com> wrote:
>>
>>> Well, as mentioned, probably Cassandra doesn’t have logic and data to
>>> skip bigger regions of deleted data based on range tombstone. If some piece
>>> of data in a partition is newer than the tombstone, then it cannot be
>>> skipped. Therefore some partition level statistics of cell ages would need
>>> to be kept in the column index for the skipping and that is probably not
>>> there.
>>>
>>> Hannu
>>>
>>> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>>>
>>> That is another way to see the question: are reverse iterators range
>>> tombstone aware? Yes.
>>> That is why I am puzzled by this afore-mentioned behavior.
>>> I would expect them to handle this case more gracefully.
>>>
>>> Cheers,
>>> Stefano
>>>
>>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
>>>
>>>> Hannu,
>>>>
>>>> How can you read a partition in reverse?
>>>>
>>>> Sent from my iPhone
>>>>
>>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>>>> >
>>>> > Well, I’m guessing that Cassandra doesn't really know if the range
>>>> tombstone is useful for this or not.
>>>> >
>>>> > In many cases it might be that the partition contains data that is
>>>> within the range of the tombstone but is newer than the tombstone and
>>>> therefore it might be still be returned. Scanning through deleted data can
>>>> be avoided by reading the partition in reverse (if all the deleted data is
>>>> in the beginning of the partition). Eventually you will still end up
>>>> reading a lot of tombstones but you will get a lot of live data first and
>>>> the implicit query limit of 10000 probably is reached before you get to the
>>>> tombstones. Therefore you will get an immediate answer.
>>>> >
>>>> > Does it make sense?
>>>> >
>>>> > Hannu
>>>> >
>>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com>
>>>> wrote:
>>>> >>
>>>> >> Hi all,
>>>> >>
>>>> >> I am seeing inconsistencies when mixing range tombstones, wide
>>>> partitions, and reverse iterators.
>>>> >> I still have to understand if the behaviour is to be expected hence
>>>> the message on the mailing list.
>>>> >>
>>>> >> The situation is conceptually simple. I am using a table defined as
>>>> follows:
>>>> >>
>>>> >> CREATE TABLE test_cql.test_cf (
>>>> >> hash blob,
>>>> >> timeid timeuuid,
>>>> >> PRIMARY KEY (hash, timeid)
>>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>>> >>
>>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain
>>>> a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
>>>> _half_ of that partition by executing the query below, and restart the node:
>>>> >>
>>>> >> DELETE
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = x AND timeid < y;
>>>> >>
>>>> >> If I keep compactions disabled the following query timeouts (takes
>>>> more than 10 seconds to
>>>> >> succeed):
>>>> >>
>>>> >> SELECT *
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>> >> ORDER BY timeid ASC;
>>>> >>
>>>> >> While the following returns immediately (obviously because no
>>>> deleted data is ever read):
>>>> >>
>>>> >> SELECT *
>>>> >> FROM test_cql.test_cf
>>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>>> >> ORDER BY timeid DESC;
>>>> >>
>>>> >> If I force a compaction the problem is gone, but I presume just
>>>> because the data is rearranged.
>>>> >>
>>>> >> It seems to me that reading by ASC does not make use of the range
>>>> tombstone until C* reads the
>>>> >> last sstables (which actually contains the range tombstone and is
>>>> flushed at node restart), and it wastes time reading all rows that are
>>>> actually not live anymore.
>>>> >>
>>>> >> Is this expected? Should the range tombstone actually help in these
>>>> cases?
>>>> >>
>>>> >> Thanks a lot!
>>>> >> Stefano
>>>> >
>>>> >
>>>> > ---------------------------------------------------------------------
>>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>>>> > For additional commands, e-mail: user-help@cassandra.apache.org
>>>> >
>>>>
>>>
>>>
>>>
>>
>>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
Yes, that was my intention but I wanted to cross-check with the ML and the
devs keeping an eye on it first.
On Tue, May 16, 2017 at 5:10 PM, Hannu Kröger <hk...@gmail.com> wrote:
> Well,
>
> sstables contain some statistics about the cell timestamps and using that
> information and the tombstone timestamp it might be possible to skip some
> data but I’m not sure that Cassandra currently does that. Maybe it would be
> worth a JIRA ticket and see what the devs think about it. If optimizing
> this case would make sense.
>
> Hannu
>
> On 16 May 2017, at 18:03, Stefano Ortolani <os...@gmail.com> wrote:
>
> Hi Hannu,
>
> the piece of data in question is older. In my example the tombstone is the
> newest piece of data.
> Since a range tombstone has information re the clustering key ranges, and
> the data is clustering key sorted, I would expect a linear scan not to be
> necessary.
>
> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hk...@gmail.com> wrote:
>
>> Well, as mentioned, probably Cassandra doesn’t have logic and data to
>> skip bigger regions of deleted data based on range tombstone. If some piece
>> of data in a partition is newer than the tombstone, then it cannot be
>> skipped. Therefore some partition level statistics of cell ages would need
>> to be kept in the column index for the skipping and that is probably not
>> there.
>>
>> Hannu
>>
>> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>>
>> That is another way to see the question: are reverse iterators range
>> tombstone aware? Yes.
>> That is why I am puzzled by this afore-mentioned behavior.
>> I would expect them to handle this case more gracefully.
>>
>> Cheers,
>> Stefano
>>
>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
>>
>>> Hannu,
>>>
>>> How can you read a partition in reverse?
>>>
>>> Sent from my iPhone
>>>
>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>>> >
>>> > Well, I’m guessing that Cassandra doesn't really know if the range
>>> tombstone is useful for this or not.
>>> >
>>> > In many cases it might be that the partition contains data that is
>>> within the range of the tombstone but is newer than the tombstone and
>>> therefore it might be still be returned. Scanning through deleted data can
>>> be avoided by reading the partition in reverse (if all the deleted data is
>>> in the beginning of the partition). Eventually you will still end up
>>> reading a lot of tombstones but you will get a lot of live data first and
>>> the implicit query limit of 10000 probably is reached before you get to the
>>> tombstones. Therefore you will get an immediate answer.
>>> >
>>> > Does it make sense?
>>> >
>>> > Hannu
>>> >
>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com>
>>> wrote:
>>> >>
>>> >> Hi all,
>>> >>
>>> >> I am seeing inconsistencies when mixing range tombstones, wide
>>> partitions, and reverse iterators.
>>> >> I still have to understand if the behaviour is to be expected hence
>>> the message on the mailing list.
>>> >>
>>> >> The situation is conceptually simple. I am using a table defined as
>>> follows:
>>> >>
>>> >> CREATE TABLE test_cql.test_cf (
>>> >> hash blob,
>>> >> timeid timeuuid,
>>> >> PRIMARY KEY (hash, timeid)
>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>> >>
>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain
>>> a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
>>> _half_ of that partition by executing the query below, and restart the node:
>>> >>
>>> >> DELETE
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = x AND timeid < y;
>>> >>
>>> >> If I keep compactions disabled the following query timeouts (takes
>>> more than 10 seconds to
>>> >> succeed):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid ASC;
>>> >>
>>> >> While the following returns immediately (obviously because no deleted
>>> data is ever read):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid DESC;
>>> >>
>>> >> If I force a compaction the problem is gone, but I presume just
>>> because the data is rearranged.
>>> >>
>>> >> It seems to me that reading by ASC does not make use of the range
>>> tombstone until C* reads the
>>> >> last sstables (which actually contains the range tombstone and is
>>> flushed at node restart), and it wastes time reading all rows that are
>>> actually not live anymore.
>>> >>
>>> >> Is this expected? Should the range tombstone actually help in these
>>> cases?
>>> >>
>>> >> Thanks a lot!
>>> >> Stefano
>>> >
>>> >
>>> > ---------------------------------------------------------------------
>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>>> > For additional commands, e-mail: user-help@cassandra.apache.org
>>> >
>>>
>>
>>
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
Well,
sstables contain some statistics about the cell timestamps and using that information and the tombstone timestamp it might be possible to skip some data but I’m not sure that Cassandra currently does that. Maybe it would be worth a JIRA ticket and see what the devs think about it. If optimizing this case would make sense.
Hannu
> On 16 May 2017, at 18:03, Stefano Ortolani <os...@gmail.com> wrote:
>
> Hi Hannu,
>
> the piece of data in question is older. In my example the tombstone is the newest piece of data.
> Since a range tombstone has information re the clustering key ranges, and the data is clustering key sorted, I would expect a linear scan not to be necessary.
>
> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
>
> Hannu
>
>> On 16 May 2017, at 17:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>
>> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
>> That is why I am puzzled by this afore-mentioned behavior.
>> I would expect them to handle this case more gracefully.
>>
>> Cheers,
>> Stefano
>>
>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
>> Hannu,
>>
>> How can you read a partition in reverse?
>>
>> Sent from my iPhone
>>
>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>> >
>> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>> >
>> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>> >
>> > Does it make sense?
>> >
>> > Hannu
>> >
>> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>> >>
>> >> The situation is conceptually simple. I am using a table defined as follows:
>> >>
>> >> CREATE TABLE test_cql.test_cf (
>> >> hash blob,
>> >> timeid timeuuid,
>> >> PRIMARY KEY (hash, timeid)
>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>> >>
>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>> >>
>> >> DELETE
>> >> FROM test_cql.test_cf
>> >> WHERE hash = x AND timeid < y;
>> >>
>> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>> >> succeed):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid ASC;
>> >>
>> >> While the following returns immediately (obviously because no deleted data is ever read):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid DESC;
>> >>
>> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>> >>
>> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>> >>
>> >> Is this expected? Should the range tombstone actually help in these cases?
>> >>
>> >> Thanks a lot!
>> >> Stefano
>> >
>> >
>> > ---------------------------------------------------------------------
>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
>> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
>> >
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Nitan Kainth <ni...@bamlabs.com>.
Thank you Stefano
> On May 16, 2017, at 10:56 AM, Stefano Ortolani <os...@gmail.com> wrote:
>
> No, because C* has reverse iterators.
>
> On Tue, May 16, 2017 at 4:47 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
> If the data is stored in ASC order and query asks for DESC, then wouldn’t it read whole partition in first and then pick data from reverse order?
>
>
>> On May 16, 2017, at 10:03 AM, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>
>> Hi Hannu,
>>
>> the piece of data in question is older. In my example the tombstone is the newest piece of data.
>> Since a range tombstone has information re the clustering key ranges, and the data is clustering key sorted, I would expect a linear scan not to be necessary.
>>
>> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
>>
>> Hannu
>>
>>> On 16 May 2017, at 17:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>>
>>> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
>>> That is why I am puzzled by this afore-mentioned behavior.
>>> I would expect them to handle this case more gracefully.
>>>
>>> Cheers,
>>> Stefano
>>>
>>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
>>> Hannu,
>>>
>>> How can you read a partition in reverse?
>>>
>>> Sent from my iPhone
>>>
>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>>> >
>>> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>>> >
>>> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>>> >
>>> > Does it make sense?
>>> >
>>> > Hannu
>>> >
>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>> >>
>>> >> Hi all,
>>> >>
>>> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>>> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>>> >>
>>> >> The situation is conceptually simple. I am using a table defined as follows:
>>> >>
>>> >> CREATE TABLE test_cql.test_cf (
>>> >> hash blob,
>>> >> timeid timeuuid,
>>> >> PRIMARY KEY (hash, timeid)
>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>> >>
>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>>> >>
>>> >> DELETE
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = x AND timeid < y;
>>> >>
>>> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>>> >> succeed):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid ASC;
>>> >>
>>> >> While the following returns immediately (obviously because no deleted data is ever read):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid DESC;
>>> >>
>>> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>>> >>
>>> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>>> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>>> >>
>>> >> Is this expected? Should the range tombstone actually help in these cases?
>>> >>
>>> >> Thanks a lot!
>>> >> Stefano
>>> >
>>> >
>>> > ---------------------------------------------------------------------
>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
>>> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
>>> >
>>>
>>
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
No, because C* has reverse iterators.
On Tue, May 16, 2017 at 4:47 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
> If the data is stored in ASC order and query asks for DESC, then wouldn’t
> it read whole partition in first and then pick data from reverse order?
>
>
> On May 16, 2017, at 10:03 AM, Stefano Ortolani <os...@gmail.com> wrote:
>
> Hi Hannu,
>
> the piece of data in question is older. In my example the tombstone is the
> newest piece of data.
> Since a range tombstone has information re the clustering key ranges, and
> the data is clustering key sorted, I would expect a linear scan not to be
> necessary.
>
> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hk...@gmail.com> wrote:
>
>> Well, as mentioned, probably Cassandra doesn’t have logic and data to
>> skip bigger regions of deleted data based on range tombstone. If some piece
>> of data in a partition is newer than the tombstone, then it cannot be
>> skipped. Therefore some partition level statistics of cell ages would need
>> to be kept in the column index for the skipping and that is probably not
>> there.
>>
>> Hannu
>>
>> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>>
>> That is another way to see the question: are reverse iterators range
>> tombstone aware? Yes.
>> That is why I am puzzled by this afore-mentioned behavior.
>> I would expect them to handle this case more gracefully.
>>
>> Cheers,
>> Stefano
>>
>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
>>
>>> Hannu,
>>>
>>> How can you read a partition in reverse?
>>>
>>> Sent from my iPhone
>>>
>>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>>> >
>>> > Well, I’m guessing that Cassandra doesn't really know if the range
>>> tombstone is useful for this or not.
>>> >
>>> > In many cases it might be that the partition contains data that is
>>> within the range of the tombstone but is newer than the tombstone and
>>> therefore it might be still be returned. Scanning through deleted data can
>>> be avoided by reading the partition in reverse (if all the deleted data is
>>> in the beginning of the partition). Eventually you will still end up
>>> reading a lot of tombstones but you will get a lot of live data first and
>>> the implicit query limit of 10000 probably is reached before you get to the
>>> tombstones. Therefore you will get an immediate answer.
>>> >
>>> > Does it make sense?
>>> >
>>> > Hannu
>>> >
>>> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com>
>>> wrote:
>>> >>
>>> >> Hi all,
>>> >>
>>> >> I am seeing inconsistencies when mixing range tombstones, wide
>>> partitions, and reverse iterators.
>>> >> I still have to understand if the behaviour is to be expected hence
>>> the message on the mailing list.
>>> >>
>>> >> The situation is conceptually simple. I am using a table defined as
>>> follows:
>>> >>
>>> >> CREATE TABLE test_cql.test_cf (
>>> >> hash blob,
>>> >> timeid timeuuid,
>>> >> PRIMARY KEY (hash, timeid)
>>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>> >>
>>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain
>>> a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
>>> _half_ of that partition by executing the query below, and restart the node:
>>> >>
>>> >> DELETE
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = x AND timeid < y;
>>> >>
>>> >> If I keep compactions disabled the following query timeouts (takes
>>> more than 10 seconds to
>>> >> succeed):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid ASC;
>>> >>
>>> >> While the following returns immediately (obviously because no deleted
>>> data is ever read):
>>> >>
>>> >> SELECT *
>>> >> FROM test_cql.test_cf
>>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> >> ORDER BY timeid DESC;
>>> >>
>>> >> If I force a compaction the problem is gone, but I presume just
>>> because the data is rearranged.
>>> >>
>>> >> It seems to me that reading by ASC does not make use of the range
>>> tombstone until C* reads the
>>> >> last sstables (which actually contains the range tombstone and is
>>> flushed at node restart), and it wastes time reading all rows that are
>>> actually not live anymore.
>>> >>
>>> >> Is this expected? Should the range tombstone actually help in these
>>> cases?
>>> >>
>>> >> Thanks a lot!
>>> >> Stefano
>>> >
>>> >
>>> > ---------------------------------------------------------------------
>>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>>> > For additional commands, e-mail: user-help@cassandra.apache.org
>>> >
>>>
>>
>>
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Nitan Kainth <ni...@bamlabs.com>.
If the data is stored in ASC order and query asks for DESC, then wouldn’t it read whole partition in first and then pick data from reverse order?
> On May 16, 2017, at 10:03 AM, Stefano Ortolani <os...@gmail.com> wrote:
>
> Hi Hannu,
>
> the piece of data in question is older. In my example the tombstone is the newest piece of data.
> Since a range tombstone has information re the clustering key ranges, and the data is clustering key sorted, I would expect a linear scan not to be necessary.
>
> On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
>
> Hannu
>
>> On 16 May 2017, at 17:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>>
>> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
>> That is why I am puzzled by this afore-mentioned behavior.
>> I would expect them to handle this case more gracefully.
>>
>> Cheers,
>> Stefano
>>
>> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
>> Hannu,
>>
>> How can you read a partition in reverse?
>>
>> Sent from my iPhone
>>
>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
>> >
>> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>> >
>> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>> >
>> > Does it make sense?
>> >
>> > Hannu
>> >
>> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>> >>
>> >> The situation is conceptually simple. I am using a table defined as follows:
>> >>
>> >> CREATE TABLE test_cql.test_cf (
>> >> hash blob,
>> >> timeid timeuuid,
>> >> PRIMARY KEY (hash, timeid)
>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>> >>
>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>> >>
>> >> DELETE
>> >> FROM test_cql.test_cf
>> >> WHERE hash = x AND timeid < y;
>> >>
>> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>> >> succeed):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid ASC;
>> >>
>> >> While the following returns immediately (obviously because no deleted data is ever read):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid DESC;
>> >>
>> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>> >>
>> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>> >>
>> >> Is this expected? Should the range tombstone actually help in these cases?
>> >>
>> >> Thanks a lot!
>> >> Stefano
>> >
>> >
>> > ---------------------------------------------------------------------
>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
>> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
>> >
>>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
Hi Hannu,
the piece of data in question is older. In my example the tombstone is the
newest piece of data.
Since a range tombstone has information re the clustering key ranges, and
the data is clustering key sorted, I would expect a linear scan not to be
necessary.
On Tue, May 16, 2017 at 3:46 PM, Hannu Kröger <hk...@gmail.com> wrote:
> Well, as mentioned, probably Cassandra doesn’t have logic and data to skip
> bigger regions of deleted data based on range tombstone. If some piece of
> data in a partition is newer than the tombstone, then it cannot be skipped.
> Therefore some partition level statistics of cell ages would need to be
> kept in the column index for the skipping and that is probably not there.
>
> Hannu
>
> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>
> That is another way to see the question: are reverse iterators range
> tombstone aware? Yes.
> That is why I am puzzled by this afore-mentioned behavior.
> I would expect them to handle this case more gracefully.
>
> Cheers,
> Stefano
>
> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
>
>> Hannu,
>>
>> How can you read a partition in reverse?
>>
>> Sent from my iPhone
>>
>> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>> >
>> > Well, I’m guessing that Cassandra doesn't really know if the range
>> tombstone is useful for this or not.
>> >
>> > In many cases it might be that the partition contains data that is
>> within the range of the tombstone but is newer than the tombstone and
>> therefore it might be still be returned. Scanning through deleted data can
>> be avoided by reading the partition in reverse (if all the deleted data is
>> in the beginning of the partition). Eventually you will still end up
>> reading a lot of tombstones but you will get a lot of live data first and
>> the implicit query limit of 10000 probably is reached before you get to the
>> tombstones. Therefore you will get an immediate answer.
>> >
>> > Does it make sense?
>> >
>> > Hannu
>> >
>> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> I am seeing inconsistencies when mixing range tombstones, wide
>> partitions, and reverse iterators.
>> >> I still have to understand if the behaviour is to be expected hence
>> the message on the mailing list.
>> >>
>> >> The situation is conceptually simple. I am using a table defined as
>> follows:
>> >>
>> >> CREATE TABLE test_cql.test_cf (
>> >> hash blob,
>> >> timeid timeuuid,
>> >> PRIMARY KEY (hash, timeid)
>> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
>> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>> >>
>> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a
>> really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
>> _half_ of that partition by executing the query below, and restart the node:
>> >>
>> >> DELETE
>> >> FROM test_cql.test_cf
>> >> WHERE hash = x AND timeid < y;
>> >>
>> >> If I keep compactions disabled the following query timeouts (takes
>> more than 10 seconds to
>> >> succeed):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid ASC;
>> >>
>> >> While the following returns immediately (obviously because no deleted
>> data is ever read):
>> >>
>> >> SELECT *
>> >> FROM test_cql.test_cf
>> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> >> ORDER BY timeid DESC;
>> >>
>> >> If I force a compaction the problem is gone, but I presume just
>> because the data is rearranged.
>> >>
>> >> It seems to me that reading by ASC does not make use of the range
>> tombstone until C* reads the
>> >> last sstables (which actually contains the range tombstone and is
>> flushed at node restart), and it wastes time reading all rows that are
>> actually not live anymore.
>> >>
>> >> Is this expected? Should the range tombstone actually help in these
>> cases?
>> >>
>> >> Thanks a lot!
>> >> Stefano
>> >
>> >
>> > ---------------------------------------------------------------------
>> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>> > For additional commands, e-mail: user-help@cassandra.apache.org
>> >
>>
>
>
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
Well, as mentioned, probably Cassandra doesn’t have logic and data to skip bigger regions of deleted data based on range tombstone. If some piece of data in a partition is newer than the tombstone, then it cannot be skipped. Therefore some partition level statistics of cell ages would need to be kept in the column index for the skipping and that is probably not there.
Hannu
> On 16 May 2017, at 17:33, Stefano Ortolani <os...@gmail.com> wrote:
>
> That is another way to see the question: are reverse iterators range tombstone aware? Yes.
> That is why I am puzzled by this afore-mentioned behavior.
> I would expect them to handle this case more gracefully.
>
> Cheers,
> Stefano
>
> On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <nitan@bamlabs.com <ma...@bamlabs.com>> wrote:
> Hannu,
>
> How can you read a partition in reverse?
>
> Sent from my iPhone
>
> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hkroger@gmail.com <ma...@gmail.com>> wrote:
> >
> > Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
> >
> > In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
> >
> > Does it make sense?
> >
> > Hannu
> >
> >> On 16 May 2017, at 16:33, Stefano Ortolani <ostefano@gmail.com <ma...@gmail.com>> wrote:
> >>
> >> Hi all,
> >>
> >> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
> >> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
> >>
> >> The situation is conceptually simple. I am using a table defined as follows:
> >>
> >> CREATE TABLE test_cql.test_cf (
> >> hash blob,
> >> timeid timeuuid,
> >> PRIMARY KEY (hash, timeid)
> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
> >>
> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
> >>
> >> DELETE
> >> FROM test_cql.test_cf
> >> WHERE hash = x AND timeid < y;
> >>
> >> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
> >> succeed):
> >>
> >> SELECT *
> >> FROM test_cql.test_cf
> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> >> ORDER BY timeid ASC;
> >>
> >> While the following returns immediately (obviously because no deleted data is ever read):
> >>
> >> SELECT *
> >> FROM test_cql.test_cf
> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> >> ORDER BY timeid DESC;
> >>
> >> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
> >>
> >> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
> >> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
> >>
> >> Is this expected? Should the range tombstone actually help in these cases?
> >>
> >> Thanks a lot!
> >> Stefano
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org <ma...@cassandra.apache.org>
> > For additional commands, e-mail: user-help@cassandra.apache.org <ma...@cassandra.apache.org>
> >
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Stefano Ortolani <os...@gmail.com>.
That is another way to see the question: are reverse iterators range
tombstone aware? Yes.
That is why I am puzzled by this afore-mentioned behavior.
I would expect them to handle this case more gracefully.
Cheers,
Stefano
On Tue, May 16, 2017 at 3:29 PM, Nitan Kainth <ni...@bamlabs.com> wrote:
> Hannu,
>
> How can you read a partition in reverse?
>
> Sent from my iPhone
>
> > On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
> >
> > Well, I’m guessing that Cassandra doesn't really know if the range
> tombstone is useful for this or not.
> >
> > In many cases it might be that the partition contains data that is
> within the range of the tombstone but is newer than the tombstone and
> therefore it might be still be returned. Scanning through deleted data can
> be avoided by reading the partition in reverse (if all the deleted data is
> in the beginning of the partition). Eventually you will still end up
> reading a lot of tombstones but you will get a lot of live data first and
> the implicit query limit of 10000 probably is reached before you get to the
> tombstones. Therefore you will get an immediate answer.
> >
> > Does it make sense?
> >
> > Hannu
> >
> >> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com> wrote:
> >>
> >> Hi all,
> >>
> >> I am seeing inconsistencies when mixing range tombstones, wide
> partitions, and reverse iterators.
> >> I still have to understand if the behaviour is to be expected hence the
> message on the mailing list.
> >>
> >> The situation is conceptually simple. I am using a table defined as
> follows:
> >>
> >> CREATE TABLE test_cql.test_cf (
> >> hash blob,
> >> timeid timeuuid,
> >> PRIMARY KEY (hash, timeid)
> >> ) WITH CLUSTERING ORDER BY (timeid ASC)
> >> AND compaction = {'class' : 'LeveledCompactionStrategy'};
> >>
> >> I then proceed by loading 2/3GB from 3 sstables which I know contain a
> really wide partition (> 512 MB) for `hash = x`. I then delete the oldest
> _half_ of that partition by executing the query below, and restart the node:
> >>
> >> DELETE
> >> FROM test_cql.test_cf
> >> WHERE hash = x AND timeid < y;
> >>
> >> If I keep compactions disabled the following query timeouts (takes more
> than 10 seconds to
> >> succeed):
> >>
> >> SELECT *
> >> FROM test_cql.test_cf
> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> >> ORDER BY timeid ASC;
> >>
> >> While the following returns immediately (obviously because no deleted
> data is ever read):
> >>
> >> SELECT *
> >> FROM test_cql.test_cf
> >> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> >> ORDER BY timeid DESC;
> >>
> >> If I force a compaction the problem is gone, but I presume just because
> the data is rearranged.
> >>
> >> It seems to me that reading by ASC does not make use of the range
> tombstone until C* reads the
> >> last sstables (which actually contains the range tombstone and is
> flushed at node restart), and it wastes time reading all rows that are
> actually not live anymore.
> >>
> >> Is this expected? Should the range tombstone actually help in these
> cases?
> >>
> >> Thanks a lot!
> >> Stefano
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
> > For additional commands, e-mail: user-help@cassandra.apache.org
> >
>
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
Hello,
If you mean how to construct a query like that: you use ORDER BY clause with SELECT which is reverse to the default just like in the example below? If the table is constructed with "clustering order by (timeid ASC)” and you query “SELECT ... ORDER BY timeid DESC”, then the partition is read backwards. I don’t know how it is technically done but it is apparently slightly slower then reading partition normally.
Hannu
> On 16 May 2017, at 17:29, Nitan Kainth <ni...@bamlabs.com> wrote:
>
> Hannu,
>
> How can you read a partition in reverse?
>
> Sent from my iPhone
>
>> On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>>
>> Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>>
>> In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>>
>> Does it make sense?
>>
>> Hannu
>>
>>> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com> wrote:
>>>
>>> Hi all,
>>>
>>> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>>> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>>>
>>> The situation is conceptually simple. I am using a table defined as follows:
>>>
>>> CREATE TABLE test_cql.test_cf (
>>> hash blob,
>>> timeid timeuuid,
>>> PRIMARY KEY (hash, timeid)
>>> ) WITH CLUSTERING ORDER BY (timeid ASC)
>>> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>>
>>> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>>>
>>> DELETE
>>> FROM test_cql.test_cf
>>> WHERE hash = x AND timeid < y;
>>>
>>> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>>> succeed):
>>>
>>> SELECT *
>>> FROM test_cql.test_cf
>>> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> ORDER BY timeid ASC;
>>>
>>> While the following returns immediately (obviously because no deleted data is ever read):
>>>
>>> SELECT *
>>> FROM test_cql.test_cf
>>> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>>> ORDER BY timeid DESC;
>>>
>>> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>>>
>>> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>>> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>>>
>>> Is this expected? Should the range tombstone actually help in these cases?
>>>
>>> Thanks a lot!
>>> Stefano
>>
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
>> For additional commands, e-mail: user-help@cassandra.apache.org
>>
---------------------------------------------------------------------
To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
For additional commands, e-mail: user-help@cassandra.apache.org
Re: Range deletes, wide partitions, and reverse iterators
Posted by Nitan Kainth <ni...@bamlabs.com>.
Hannu,
How can you read a partition in reverse?
Sent from my iPhone
> On May 16, 2017, at 9:20 AM, Hannu Kröger <hk...@gmail.com> wrote:
>
> Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
>
> In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
>
> Does it make sense?
>
> Hannu
>
>> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com> wrote:
>>
>> Hi all,
>>
>> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
>> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>>
>> The situation is conceptually simple. I am using a table defined as follows:
>>
>> CREATE TABLE test_cql.test_cf (
>> hash blob,
>> timeid timeuuid,
>> PRIMARY KEY (hash, timeid)
>> ) WITH CLUSTERING ORDER BY (timeid ASC)
>> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>>
>> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>>
>> DELETE
>> FROM test_cql.test_cf
>> WHERE hash = x AND timeid < y;
>>
>> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
>> succeed):
>>
>> SELECT *
>> FROM test_cql.test_cf
>> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> ORDER BY timeid ASC;
>>
>> While the following returns immediately (obviously because no deleted data is ever read):
>>
>> SELECT *
>> FROM test_cql.test_cf
>> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
>> ORDER BY timeid DESC;
>>
>> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>>
>> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
>> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>>
>> Is this expected? Should the range tombstone actually help in these cases?
>>
>> Thanks a lot!
>> Stefano
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
> For additional commands, e-mail: user-help@cassandra.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org
For additional commands, e-mail: user-help@cassandra.apache.org
Re: Range deletes, wide partitions, and reverse iterators
Posted by Hannu Kröger <hk...@gmail.com>.
Well, I’m guessing that Cassandra doesn't really know if the range tombstone is useful for this or not.
In many cases it might be that the partition contains data that is within the range of the tombstone but is newer than the tombstone and therefore it might be still be returned. Scanning through deleted data can be avoided by reading the partition in reverse (if all the deleted data is in the beginning of the partition). Eventually you will still end up reading a lot of tombstones but you will get a lot of live data first and the implicit query limit of 10000 probably is reached before you get to the tombstones. Therefore you will get an immediate answer.
Does it make sense?
Hannu
> On 16 May 2017, at 16:33, Stefano Ortolani <os...@gmail.com> wrote:
>
> Hi all,
>
> I am seeing inconsistencies when mixing range tombstones, wide partitions, and reverse iterators.
> I still have to understand if the behaviour is to be expected hence the message on the mailing list.
>
> The situation is conceptually simple. I am using a table defined as follows:
>
> CREATE TABLE test_cql.test_cf (
> hash blob,
> timeid timeuuid,
> PRIMARY KEY (hash, timeid)
> ) WITH CLUSTERING ORDER BY (timeid ASC)
> AND compaction = {'class' : 'LeveledCompactionStrategy'};
>
> I then proceed by loading 2/3GB from 3 sstables which I know contain a really wide partition (> 512 MB) for `hash = x`. I then delete the oldest _half_ of that partition by executing the query below, and restart the node:
>
> DELETE
> FROM test_cql.test_cf
> WHERE hash = x AND timeid < y;
>
> If I keep compactions disabled the following query timeouts (takes more than 10 seconds to
> succeed):
>
> SELECT *
> FROM test_cql.test_cf
> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> ORDER BY timeid ASC;
>
> While the following returns immediately (obviously because no deleted data is ever read):
>
> SELECT *
> FROM test_cql.test_cf
> WHERE hash = 0x963204d451de3e611daf5e340c3594acead0eaaf
> ORDER BY timeid DESC;
>
> If I force a compaction the problem is gone, but I presume just because the data is rearranged.
>
> It seems to me that reading by ASC does not make use of the range tombstone until C* reads the
> last sstables (which actually contains the range tombstone and is flushed at node restart), and it wastes time reading all rows that are actually not live anymore.
>
> Is this expected? Should the range tombstone actually help in these cases?
>
> Thanks a lot!
> Stefano
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