[jira] [Created] (CASSANDRA-8342) Remove historical guidance for concurrent reader and tunings.

["Matt Stump (JIRA)" <ji...@apache.org>]

Matt Stump created CASSANDRA-8342:
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             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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