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https://issues.apache.org/jira/browse/CASSANDRA-8342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14225427#comment-14225427
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Ryan McGuire commented on CASSANDRA-8342:
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http://riptano.github.io/cassandra_performance/graph_v4/graph.html?stats=stats.8342.json
Definitely agree that increasing it doesn't improve things, but not seeing much
of a dropoff either.
Per Jonathan's suggestion, this test was all in memory though. Rereading the
guidance text in the yaml would seem to suggest testing this with a load
larger, no?
> 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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