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From "Matt Stump (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-8342) Remove historical guidance for concurrent reader and tunings.
Date Wed, 19 Nov 2014 18:38:33 GMT
Matt Stump created CASSANDRA-8342:
-------------------------------------

             Summary: Remove historical guidance for concurrent reader and tunings.
                 Key: CASSANDRA-8342
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8342
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Matt Stump


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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