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https://issues.apache.org/jira/browse/CASSANDRA-15299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17226898#comment-17226898
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Sam Tunnicliffe commented on CASSANDRA-15299:
---------------------------------------------
Thanks, [~ifesdjeen], the flow chart is definitely useful (and looks correct to
me, aside from the missing labels that Caleb mentioned). Re: your comments...
{quote}in CQLMessageHeader#processLargeMessage, we seem to be creating a
LargeMessage object to call processCqlFrame() over a frame that is assembled
from a single byte buffer. Maybe we can just call processCqlFrame
directly?{quote}
thanks, removed in {{ce6223cb}}
{quote}this is probably something that we should address outside this ticket,
but still: "corrupt frame recovered" seems to be slightly misleading wording,
same as Frame#recoverable. We can not recover the frame itself, we just can
skip/drop it. Maybe we can rename this, along with metrics in Messaging, before
they become public in 4.0.{quote}
I tend to agree, maybe something which conveys that the frames are
skipped/dropped rather than recovered would be better? We can open a new JIRA
for this.
{quote}in CQLMessageHeader#processCqlFrame, we only call handleErrorAndRelease.
However, it may theoretically happen that we fail before we finish
messageDecoder.decode(channel, frame). Maybe we can do something like the [1],
to make it consistent with what we do in ProtocolDecoder#decode?{quote}
Good call, added in {{8dbf7e42}}.
{quote}in CQLMessageHeader$LargeMessage#onComplete, we wrap
processCqlFrame(assembleFrame() call in try/catch which is identical to
try/catch block from processCqlFrame itself. Just checking if this is
intended.{quote}
no, it was a redundancy left over from earlier, removed it in {{8dbf7e42}}.
{quote}in Dispatcher#processRequest, we can slightly simplify code by declaring
FlushItem<?> flushItem variable outside try/catch block and assigning a
corresponding value in try or catch, and only calling flush once.{quote}
done in {{8dbf7e42}}
{quote}during sever bootstrap initialization, we're using deprecated low/high
watermark child options, probably we should use
.childOption(ChannelOption.WRITE_BUFFER_WATER_MARK, new WriteBufferWaterMark(8
* 1024, 32 * 1024)) instead.{quote}
Thanks, fixed in {{8dbf7e42}}
{quote}SimpleClientBurnTest#random is unused{quote}
thanks, removed.
[~maedhroz], thanks, those are decent improvements and seem to me worth making.
{quote}testChangingLimitsAtRuntime has a bunch of places where it checks the
same value twice, for instance from ClientResourceLimits.getGlobalLimit() and
then DatabaseDescriptor.getNativeTransportMaxConcurrentRequestsInBytes(). Seems
like we could do away with the second?{quote}
Thanks, it is redundant for the global limit, as the {{ClientResourceLimits}}
method just delegates to {{DatabaseDescriptor}}, which was always the case I
think. For the per-endpoint limits, it's definitely worth checking both places
to ensure existing and new limits observe the same cap.
> 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-alpha
>
> Attachments: Process CQL Frame.png, V5 Flow Chart.png
>
>
> 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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