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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 Sat, 25 Apr 2015 16:31:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14512580#comment-14512580
] 

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

{quote}
Gossip always contended with mutation responses and read responses.
{quote}

No, they didn't. This is why there were two sockets in the first place. A Command and socket
and a Data socket. I have said since day one when I raised this as a concern that with changes
to Gossip (large and definitely outside the scope of 3.0) could be made so this might not
be an issue.

Today with these changes and today's Gossip implementation -- this is a regression.

> 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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