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From "Corentin Chary (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13039) Mutation time mostly spent in LinkedBlockingQueue.put()
Date Wed, 28 Dec 2016 16:32:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15783227#comment-15783227
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Corentin Chary commented on CASSANDRA-13039:
--------------------------------------------

That would make sense when using QUORUM (because you are waiting for these replicated mutation).
If you use ONE it's the opposite. I'm still trying to build a cassandra stress profile that
can easilly reproduce that.


> Mutation time mostly spent in LinkedBlockingQueue.put()
> -------------------------------------------------------
>
>                 Key: CASSANDRA-13039
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13039
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Coordination
>            Reporter: Corentin Chary
>         Attachments: mutation-linkedlist-block.png, profiler-snapshot.nps
>
>
> On a setup with a sustained write load of 70kQPS per node and a RF of 2 it looks like
most of the mutation time is spend in OutboundTcpConnection.enqueue() -> backlog.put()
> backlog is an unbounded LinkedBlockingQueue, which means that .put() can only be blocking
if a lock is taken. I strongly suspect that this is caused by the use of drainTo() in CoalescingStrategies
which is causing contention for the producers.
> On the other hand, not using drainTo() could lead to starvation of the consumers.
> Possible solutions:
> - Allow multiple connections per size and per hosts in OutboundTcpConnectionPool
> - Switch from drainTo to multiple take()
> - Switch to ConcurrentLinkedQueue (which is lockless), also means we need active polling.
> Maybe a good solution would be something hybrid: a bounded LinkedBlockingQueue and an
unbounded ConcurrentLinkedQueue. This way you get low latency when you don't have a lot of
messages, and throughput when you do.



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