[
https://issues.apache.org/jira/browse/CASSANDRA-15299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17226048#comment-17226048
]
Alex Petrov commented on CASSANDRA-15299:
-----------------------------------------
Patch looks good to me, I have only several comments:
* 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?
* 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.
* 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}}?
* 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.
* 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.
* 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.
* {{SimpleClientBurnTest#random}} is unused
If this is helpful, I've also put nits mentioned above (and a couple cleanups)
in a commit
[here|https://github.com/apache/cassandra/commit/76ee6e00f42446d94679e9c9001c81ebfa9418ab].
Not sure if this is helpful, but I've also put together a v5 flow chart, which
might be helpful if anyone wants a quick overview of what's going on in v5.
[1]
{code}
protected void processCqlFrame(Frame frame)
{
M message = null;
try
{
message = messageDecoder.decode(channel, frame);
dispatcher.accept(channel, message, this::toFlushItem);
}
catch (Exception e)
{
if (message == null)
frame.release();
handleErrorAndRelease(e, frame.header);
}
}
{code}
> 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.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org
For additional commands, e-mail: commits-h...@cassandra.apache.org
