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From "Matt Stump (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8342) Remove historical guidance for concurrent reader and writer tunings.
Date Wed, 26 Nov 2014 00:12:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14225448#comment-14225448
] 

Matt Stump commented on CASSANDRA-8342:
---------------------------------------

The customer reporting was 32 physical cores, with an entirely in memory dataset on DSE 4.0.3
(C* 2.0.7). For datasets not in memory I wouldn't expect much difference because the bottleneck
would be moved to the concurrency limit of the underlying IO system; but that's just an assertion.


> Remove historical guidance for concurrent reader and writer tunings.
> --------------------------------------------------------------------
>
>                 Key: CASSANDRA-8342
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8342
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Matt Stump
>            Assignee: Ryan McGuire
>
> The cassandra.yaml and documentation provide guidance on tuning concurrent readers or
concurrent writers to system resources (cores, spindles). Testing performed by both myself
and customers demonstrates no benefit for thread pool sizes above 64 in size, and for thread
pools greater than 128 in size a decrease in throughput. This is due to thread scheduling
and synchronization bottlenecks within Cassandra. 
> Additionally, for lower end systems reducing these thread pools provides very little
benefit because the bottleneck is typically moved to either IO or CPU.
> I propose that we set the default value to 64 (current default is 32), and remove all
guidance/recommendations regarding tuning.
> This recommendation may change in 3.0, but that would require further experimentation.



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