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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8789) Revisit how OutboundTcpConnection pools two connections for different message types
Date Wed, 11 Feb 2015 18:34:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14316731#comment-14316731
] 

Benedict commented on CASSANDRA-8789:
-------------------------------------

I think it makes more sense to have separate queues for each message type, that we round-robin
over, so that a lot of large messages of one type can never unduly delay small messages of
another. This permits us to coalesce more messages (with or without the coalescing patch of
CASSANDRA-8692)

> Revisit how OutboundTcpConnection pools two connections for different message types
> -----------------------------------------------------------------------------------
>
>                 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
>
> 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 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.



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