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From "Matt Stump (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-9242) Add PerfDisableSharedMem to default JVM params
Date Fri, 24 Apr 2015 23:31:40 GMT
Matt Stump created CASSANDRA-9242:
-------------------------------------

             Summary: Add PerfDisableSharedMem to default JVM params
                 Key: CASSANDRA-9242
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9242
             Project: Cassandra
          Issue Type: Improvement
          Components: Config
            Reporter: Matt Stump


We should add PerfDisableSharedMem to default JVM params. The JVM will save stats to a memory
mapped file when reaching a safepoint. This is performed synchronously and the JVM remains
paused while this action takes place. Occasionally the OS will stall the calling thread while
this happens resulting in significant impact to worst case JVM pauses. By disabling the save
in the JVM these mysterious multi-second pauses disappear.

The behavior is outlined in [this article|http://www.evanjones.ca/jvm-mmap-pause.html]. Another
manifestation is significant time spent in sys during GC pauses. In [the linked test|http://cstar.datastax.com/graph?stats=762d9c2a-eace-11e4-8236-42010af0688f&metric=gc_max_ms&operation=1_write&smoothing=1&show_aggregates=true&xmin=0&xmax=110.77&ymin=0&ymax=10421.4]
you'll notice multiple seconds spent in sys during the longest pauses.




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