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From "Michael Kjellman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8789) OutboundTcpConnectionPool should route messages to sockets by size not type
Date Thu, 23 Apr 2015 22:22:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14509954#comment-14509954
] 

Michael Kjellman commented on CASSANDRA-8789:
---------------------------------------------

I'm less concerned about hints being generated in general. With the old stress + defaults
(and RF=3 to generate lots of MUTATIONS between nodes) hints will be generated bc we never
will be able to keep up and send all of the REQUEST_RESPONSE before we see timeouts.

The real concern I have is that Gossiper/FD will kick in and DOWN healthy up nodes simply
because we can't get gossip messages out onto the wire as they backup behind all of the REQUEST_RESPONSE
messages...

> 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.



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