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From "Nate McCall (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-10702) Statement concerning default ParallelGCThreads in jvm.options is not correct
Date Fri, 13 Nov 2015 21:36:10 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-10702?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Nate McCall updated CASSANDRA-10702:
------------------------------------
    Attachment: 10702.patch

Changes the comment to better explain the defaults for G1GC

> Statement concerning default ParallelGCThreads in jvm.options is not correct
> ----------------------------------------------------------------------------
>
>                 Key: CASSANDRA-10702
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10702
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Configuration
>            Reporter: Nate McCall
>            Priority: Trivial
>         Attachments: 10702.patch
>
>
> from {{jvm.options}}:
> bq. 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:
> {noformat}
> [Parallel Time: 342.6 ms, GC Workers: 16]
> {noformat}
> on a 24 core system in this case. 



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