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  1. Cassandra
  2. CASSANDRA-10702

Statement concerning default ParallelGCThreads in jvm.options is not correct

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Details

    • Bug
    • Status: Resolved
    • Low
    • Resolution: Fixed
    • 3.0.1, 3.1
    • Local/Config
    • None
    • Low

    Description

      from jvm.options:

      The JVM maximum is 8 PGC threads and 1/4 of that for ConcGC.

      This is not correct. If there are more than eight CPUs, the default becomes 5/8 of the number of CPUs rounded up to the nearest even number (it seems - see below). See -XX:ParallelGCThreads=n secion of http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html

      Pretty easy to test with > 16 cores (as 5/8 of such is 10): turn on GC logging, leave the defaults, and the G1GC output will show something like:

      [Parallel Time: 342.6 ms, GC Workers: 16]
      

      on a 24 core system in this case.

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            zznate Nate McCall Assign to me
            zznate Nate McCall
            Nate McCall
            Paulo Motta
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