[
https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14324683#comment-14324683
]
Benedict commented on CASSANDRA-8789:
-------------------------------------
It's a nice neat patch. It might be worth commenting on the payloadSize
memoization that we piggyback on visibility guarantees of the queue we use to
pass the message to another thread, since we do always pass it, and that once
handed over we should never call payloadSize() again on the thread that has
handed off ownership.
When I commit I'll also clean up some legacy cruft, like some generic
parameters, and normalising the operation over both connections (in one place
we just list them both, in the other two we construct an array and iterate, I'd
prefer to do just one). But these are unrelated to this patch.
> OutboundTcpConnectionPool should route messages to sockets by size not type
> ---------------------------------------------------------------------------
>
> Key: CASSANDRA-8789
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8789
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Ariel Weisberg
> Assignee: Ariel Weisberg
> Fix For: 3.0
>
> Attachments: 8789.diff
>
>
> I was looking at this trying to understand what messages flow over which
> connection.
> For reads the request goes out over the command connection and the response
> comes back over the ack connection.
> For writes the request goes out over the command connection and the response
> comes back over the command connection.
> Reads get a dedicated socket for responses. Mutation commands and responses
> both travel over the same socket along with read requests.
> Sockets are used uni-directional so there are actually four sockets in play
> and four threads at each node (2 inbounded, 2 outbound).
> CASSANDRA-488 doesn't leave a record of what the impact of this change was.
> If someone remembers what situations were made better it would be good to
> know.
> I am not clear on when/how this is helpful. The consumer side shouldn't be
> blocking so the only head of line blocking issue is the time it takes to
> transfer data over the wire.
> If message size is the cause of blocking issues then the current design mixes
> small messages and large messages on the same connection retaining the head
> of line blocking.
> Read requests share the same connection as write requests (which are large),
> and write acknowledgments (which are small) share the same connections as
> write requests. The only winner is read acknowledgements.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
