[jira] [Commented] (CASSANDRA-13304) Add checksumming to the native protocol

["Sam Tunnicliffe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-13304?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15953522#comment-15953522 ] 

Sam Tunnicliffe commented on CASSANDRA-13304:
---------------------------------------------

Thanks much [~adutra]!

bq. Currently checksum is enforced even for STARTUP messages, is that on purpose? Given that compression is always disabled for this message, I was wondering if we shouldn't disable checksum as well.

Yes it was intentional. Compression is optional and negotiated via the STARTUP message, so I see the sense in disabling compression for that message. Because my proposal was to make checksumming mandatory for v5+ there's no particular reason to skip checksums for STARTUP. If the consensus we arrive it is to make it optional, then disabling it there would be necessary.

bq. Currently if checksum fails an IOException is thrown which is caught by UnexpectedChannelExceptionHandler and the connection is closed. This is not very user-friendly because clients have no clue about what happened

Do you think a {{ProtocolException}} is appropriate here, or do we need to define a new error response?

bq. Minor: ChunkCompressor.compressChunk() is always called with srcOffset = 0 and destOffset = 0; can we simplify the signature?

We perhaps could. [~mkjellman], you expressed an intention to add more compression impls down the line. Do you see this change making that more difficult? Also, perhaps we should consider changing the {{decompress}} signature to accept a pre-allocated dest array? The LZ4 javadoc for the version of {{decompress}} we're currently using states "Warning: this method has an important overhead due to the fact that it needs to allocate a buffer to decompress into, and then needs to resize this buffer to the actual decompressed length." Incidentally, I guess it would be nice to be able to re-use the new {{LZ4Compressor}} in {{LegacyLZ4FrameCompressor}}.

bq. Nit: packages org.apache.cassandra.transport.frame and org.apache.cassandra.transport.frame.body should imo contain the word checksum because this is what they are meant for.
bq. Nit: In ChecksummedFrameCompressor and ChecksummedTransformer I would replace Checksummed with Checksumming.

I've pushed [a commit|https://github.com/beobal/cassandra/commit/f5180e1aa58e8900ed9b3612a9f1779e598a2b0a] with some renaming and a slight reorg of the packages, let me know what you think.

I've also updated the branch to make use of {{ChecksumType}} and remove the unnecessary threadlocal in the checksumming transformer.

[~mkjellman], [~adutra] asks if the use of {{Unpooled}} is necessary [here|https://github.com/beobal/cassandra/commit/5d6e46bc5b68321a98b5be6ebc44fe3a539b637e#commitcomment-21578151]. I don't think it is but was there a reason you did it like that specifically?

> Add checksumming to the native protocol
> ---------------------------------------
>
>                 Key: CASSANDRA-13304
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13304
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Michael Kjellman
>            Assignee: Michael Kjellman
>              Labels: client-impacting
>         Attachments: 13304_v1.diff
>
>
> The native binary transport implementation doesn't include checksums. This makes it highly susceptible to silently inserting corrupted data either due to hardware issues causing bit flips on the sender/client side, C*/receiver side, or network in between.
> Attaching an implementation that makes checksum'ing mandatory (assuming both client and server know about a protocol version that supports checksums) -- and also adds checksumming to clients that request compression.
> The serialized format looks something like this:
> {noformat}
>  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
>  *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |  Number of Compressed Chunks  |     Compressed Length (e1)    /
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * /  Compressed Length cont. (e1) |    Uncompressed Length (e1)   /
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * | Uncompressed Length cont. (e1)| CRC32 Checksum of Lengths (e1)|
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * | Checksum of Lengths cont. (e1)|    Compressed Bytes (e1)    +//
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                      CRC32 Checksum (e1)                     ||
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                    Compressed Length (e2)                     |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                   Uncompressed Length (e2)                    |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                CRC32 Checksum of Lengths (e2)                 |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                     Compressed Bytes (e2)                   +//
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                      CRC32 Checksum (e2)                     ||
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                    Compressed Length (en)                     |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                   Uncompressed Length (en)                    |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                CRC32 Checksum of Lengths (en)                 |
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                      Compressed Bytes (en)                  +//
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  * |                      CRC32 Checksum (en)                     ||
>  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
> {noformat}
> The first pass here adds checksums only to the actual contents of the frame body itself (and doesn't actually checksum lengths and headers). While it would be great to fully add checksuming across the entire protocol, the proposed implementation will ensure we at least catch corrupted data and likely protect ourselves pretty well anyways.
> I didn't go to the trouble of implementing a Snappy Checksum'ed Compressor implementation as it's been deprecated for a while -- is really slow and crappy compared to LZ4 -- and we should do everything in our power to make sure no one in the community is still using it. I left it in (for obvious backwards compatibility aspects) old for clients that don't know about the new protocol.
> The current protocol has a 256MB (max) frame body -- where the serialized contents are simply written in to the frame body.
> If the client sends a compression option in the startup, we will install a FrameCompressor inline. Unfortunately, we went with a decision to treat the frame body separately from the header bits etc in a given message. So, instead we put a compressor implementation in the options and then if it's not null, we push the serialized bytes for the frame body *only* thru the given FrameCompressor implementation. The existing implementations simply provide all the bytes for the frame body in one go to the compressor implementation and then serialize it with the length of the compressed bytes up front.
> Unfortunately, this won't work for checksum'ing for obvious reasons as we can't naively just checksum the entire (potentially) 256MB frame body and slap it at the end... so,
> The best place to start with the changes is in {{ChecksumedCompressor}}. I implemented one single place to perform the checksuming (and to support checksuming) the actual required chunking logic. Implementations of ChecksumedCompressor only implement the actual calls to the given compression algorithm for the provided bytes.
> Although the interface takes a {{Checksum}}, right now the attached patch uses CRC32 everywhere. As of right now, given JDK8+ has support for doing the calculation with the Intel instruction set, CRC32 is about as fast as we can get right now.
> I went with a 32kb "default" for the chunk size -- meaning we will chunk the entire frame body into 32kb chunks, compress each one of those chunks, and checksum the chunk. Upon discussing with a bunch of people and researching how checksums actually work and how much data they will protect etc -- if we use 32kb chunks with CRC32 we can catch up to 32 bits flipped in a row (but more importantly catch the more likely corruption where a single bit is flipped) with pretty high certainty. 64kb seems to introduce too much of a probability of missing corruption.
> The maximum block size LZ4 operates on is a 64kb chunk -- so this combined with the need to make sure the CRC32 checksums are actually going to catch stuff -- chunking at 32kb seemed like a good reasonable value to use when weighing both checksums and compression (to ensure we don't kill our compression ratio etc).
> I'm not including client changes here -- I asked around and I'm not really sure what the policy there is -- do we update the python driver? java driver? how has the timing of this stuff been handled in the past?



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