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From "Josh McKenzie (Jira)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-15299) CASSANDRA-13304 follow-up: improve checksumming and compression in protocol v5-beta
Date Tue, 04 Aug 2020 22:52:01 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-15299?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Josh McKenzie updated CASSANDRA-15299:
--------------------------------------
    Fix Version/s:     (was: 4.0-alpha)
                   4.0-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: Alex Petrov
>            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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