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From "Tupshin Harper (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9242) Add PerfDisableSharedMem to default JVM params
Date Sat, 25 Apr 2015 00:49:38 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14512125#comment-14512125
] 

Tupshin Harper commented on CASSANDRA-9242:
-------------------------------------------

Big plus one on this. Since that linked article came out, I've heard of a couple of cases
where this was tried, and in each case, it helped with long tail latencies.

> 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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