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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-4718) More-efficient ExecutorService for improved throughput
Date Mon, 14 Apr 2014 18:41:22 GMT


Benedict commented on CASSANDRA-4718:

I think it is unlikely that the CAS has any meaningful impact. The QPI is very quick. I think
this kind of speedup is more likely down to reduced signalling costs (unpark costs ~ 10micros,
and work stealing means you have to go to the main queue far less frequently); possibly also
the signalling of threads has been directly optimised in FJP. I knocked up a "low-switch"
executor but found fairly little benefit on my box, as I can saturate the CPUs very easily
(at which point the unpark cost is never incurred). On a many-CPU box, saturating all the
cores is difficult, and so it is much more likely you'll be introducing bottlenecks on producers
adding to the queue.

> More-efficient ExecutorService for improved throughput
> ------------------------------------------------------
>                 Key: CASSANDRA-4718
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Jason Brown
>            Priority: Minor
>              Labels: performance
>             Fix For: 2.1
>         Attachments: 4718-v1.patch,, baq vs trunk.png, op costs of
various queues.ods, stress op rate with various queues.ods, v1-stress.out
> Currently all our execution stages dequeue tasks one at a time.  This can result in contention
between producers and consumers (although we do our best to minimize this by using LinkedBlockingQueue).
> One approach to mitigating this would be to make consumer threads do more work in "bulk"
instead of just one task per dequeue.  (Producer threads tend to be single-task oriented by
nature, so I don't see an equivalent opportunity there.)
> BlockingQueue has a drainTo(collection, int) method that would be perfect for this. 
However, no ExecutorService in the jdk supports using drainTo, nor could I google one.
> What I would like to do here is create just such a beast and wire it into (at least)
the write and read stages.  (Other possible candidates for such an optimization, such as the
CommitLog and OutboundTCPConnection, are not ExecutorService-based and will need to be one-offs.)
> AbstractExecutorService may be useful.  The implementations of ICommitLogExecutorService
may also be useful. (Despite the name these are not actual ExecutorServices, although they
share the most important properties of one.)

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