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From "mlowicki (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9681) Memtable heap size grows and many long GC pauses are triggered
Date Tue, 30 Jun 2015 08:12:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14607913#comment-14607913
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mlowicki commented on CASSANDRA-9681:
-------------------------------------

https://www.dropbox.com/s/cnv36bbdznbwc0g/Screenshot%202015-06-30%2010.07.27.png?dl=0 - this
if chart from the box I was creating heap dump. Please keep in mind that the metric changes
rapidly. It can grow from ~300MB to over 1GB within 3 minutes. I'll prepare heap dump today
once again.

I'm using jmap:
{code}
root@db5:/var# jmap -F -dump:file=cassandra.bin 19189
{code}
and this C* node is dead for the rest of the cluster for ~40minutes. Can this be avoided?



> 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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