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https://issues.apache.org/jira/browse/CASSANDRA-9681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14606713#comment-14606713
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Benedict commented on CASSANDRA-9681:
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Regrettably, that heap dump also looks 100% healthy. Approximately 500Mb of
memtable space being used.
It is possible we're getting some funky reporting, somehow, but I can't see an
obvious candidate change. Could you possibly try obtaining another heap dump
when under more significant pressure?
Would be also great to get the log files for the 26th onwards, since that looks
to be where the utilisation was most spiked.
> Memtable heap size grows and many long GC pauses are triggered
> --------------------------------------------------------------
>
> Key: CASSANDRA-9681
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9681
> Project: Cassandra
> Issue Type: Bug
> Environment: C* 2.1.7, Debian Wheezy
> Reporter: mlowicki
> Assignee: Benedict
> Priority: Critical
> Fix For: 2.1.x
>
> Attachments: cassandra.yaml, system.log.6.zip, system.log.7.zip,
> system.log.8.zip, system.log.9.zip
>
>
> C* 2.1.7 cluster is behaving really bad after 1-2 days.
> {{gauges.cassandra.jmx.org.apache.cassandra.metrics.ColumnFamily.AllMemtablesHeapSize.Value}}
> jumps to 7 GB
> (https://www.dropbox.com/s/vraggy292erkzd2/Screenshot%202015-06-29%2019.12.53.png?dl=0)
> on 3/6 nodes in each data center and then there are many long GC pauses.
> Cluster is using default heap size values ({{-Xms8192M -Xmx8192M -Xmn2048M}})
> Before C* 2.1.5 memtables heap size was basically constant ~500MB
> (https://www.dropbox.com/s/fjdywik5lojstvn/Screenshot%202015-06-29%2019.30.00.png?dl=0)
> After restarting all nodes is behaves stable for 1-2days. Today I've done
> that and long GC pauses are gone (~18:00
> https://www.dropbox.com/s/7vo3ynz505rsfq3/Screenshot%202015-06-29%2019.28.37.png?dl=0).
> The only pattern we've found so far is that long GC pauses are happening
> basically at the same time on all nodes in the same data center - even on the
> ones where memtables heap size is not growing.
> Cliffs on the graphs are nodes restarts.
> Used memory on boxes where {{AllMemtabelesHeapSize}} grows, stays at the same
> level -
> https://www.dropbox.com/s/tes9abykixs86rf/Screenshot%202015-06-29%2019.37.52.png?dl=0.
> Replication factor is set to 3.
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