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Posted to commits@cassandra.apache.org by "Sam Tunnicliffe (Jira)" <ji...@apache.org> on 2020/05/01 17:19:00 UTC
[jira] [Commented] (CASSANDRA-15299) CASSANDRA-13304 follow-up:
improve checksumming and compression in protocol v5-beta
[ https://issues.apache.org/jira/browse/CASSANDRA-15299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17097525#comment-17097525 ]
Sam Tunnicliffe commented on CASSANDRA-15299:
---------------------------------------------
I've pushed a branch with preliminary patches here: https://github.com/beobal/cassandra/tree/15299-trunk
including a [note| https://github.com/beobal/cassandra/blob/15299-trunk/cql_protocol_V5_framing.asc] on the proposed format changes.
This is very much a WIP in terms of the implementation, and there is a sizeable list of outstanding {{TODOs}}, not least unit/functional/performance tests, but I wanted to get something that roughly works up to unblock driver development. I've been testing with {{SimpleClient}} and {{debug-cql}}, plus a horribly hacked version of driver 3.6 which just exercises a few types of interaction to provide a simple smoke test.
[~jorgebg], [~eduard.tudenhoefner], [~adutra], [~blerer] [~csplinter], [~aholmber] : you guys all asked me about this at some point in the recent past, so now there's something to look at. I apologise for taking so long to get to this point, but other stuff got in the way I'm afraid. Hopefully, I should have a bit more time to focus on this now and see if we can get it into shape for beta.
> CASSANDRA-13304 follow-up: improve checksumming and compression in protocol v5-beta
> -----------------------------------------------------------------------------------
>
> Key: CASSANDRA-15299
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15299
> Project: Cassandra
> Issue Type: Improvement
> Components: Messaging/Client
> Reporter: Aleksey Yeschenko
> Assignee: Sam Tunnicliffe
> Priority: Normal
> Labels: protocolv5
> Fix For: 4.0-beta
>
>
> CASSANDRA-13304 made an important improvement to our native protocol: it introduced checksumming/CRC32 to request and response bodies. It’s an important step forward, but it doesn’t cover the entire stream. In particular, the message header is not covered by a checksum or a crc, which poses a correctness issue if, for example, {{streamId}} gets corrupted.
> Additionally, we aren’t quite using CRC32 correctly, in two ways:
> 1. We are calculating the CRC32 of the *decompressed* value instead of computing the CRC32 on the bytes written on the wire - losing the properties of the CRC32. In some cases, due to this sequencing, attempting to decompress a corrupt stream can cause a segfault by LZ4.
> 2. When using CRC32, the CRC32 value is written in the incorrect byte order, also losing some of the protections.
> See https://users.ece.cmu.edu/~koopman/pubs/KoopmanCRCWebinar9May2012.pdf for explanation for the two points above.
> Separately, there are some long-standing issues with the protocol - since *way* before CASSANDRA-13304. Importantly, both checksumming and compression operate on individual message bodies rather than frames of multiple complete messages. In reality, this has several important additional downsides. To name a couple:
> # For compression, we are getting poor compression ratios for smaller messages - when operating on tiny sequences of bytes. In reality, for most small requests and responses we are discarding the compressed value as it’d be smaller than the uncompressed one - incurring both redundant allocations and compressions.
> # For checksumming and CRC32 we pay a high overhead price for small messages. 4 bytes extra is *a lot* for an empty write response, for example.
> To address the correctness issue of {{streamId}} not being covered by the checksum/CRC32 and the inefficiency in compression and checksumming/CRC32, we should switch to a framing protocol with multiple messages in a single frame.
> I suggest we reuse the framing protocol recently implemented for internode messaging in CASSANDRA-15066 to the extent that its logic can be borrowed, and that we do it before native protocol v5 graduates from beta. See https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/net/FrameDecoderCrc.java and https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/net/FrameDecoderLZ4.java.
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