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From "Peter Schuller (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1014) GC storming, possible memory leak
Date Mon, 23 Aug 2010 17:38:22 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1014?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901497#action_12901497
] 

Peter Schuller commented on CASSANDRA-1014:
-------------------------------------------

I have not read anything about this other than what is in this ticket, and the beginnings
of this is old, so this may be moot, but a couple of things:

* The first graph attached (1014-2Gheap.png) looks to me like the JVM is only doing young
generation collections and is simply not ever doing a concurrent mark/sweep phase. That would
be a VM bug (or broken VM options).

* Is the 60 mb vs. 368 mb the difference between a CMS full collection and a stop-the-world
full collection? I.e., it was 368 right after a full CMS sweep? It need not necessarily indicate
a VM bug; consider that CMS's old gen is maintained in a non-compacting/copying fashion and
that the CMS old gen is thus susceptible to fragmentation overhead. A full stop-the-world
GC also applies, AFAIK, that it does a compacting GC. A factor of 6.1 seems like a lot though,
but I don't know about how the CMS free space management works. If the 6.1 is explained by
fragmentation, my initial guess would be that large allocations are the triggering factor.

> GC storming, possible memory leak
> ---------------------------------
>
>                 Key: CASSANDRA-1014
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1014
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.6
>         Environment: debian lenny amd64 OpenJDK 64-Bit Server VM (build 1.6.0_0-b11,
mixed mode)
>            Reporter: Brandon Williams
>             Fix For: 0.7.0
>
>         Attachments: 1014-2Gheap.png, 1014-commitlog-v2.tar.gz, 1014-table.diff, 724-0001.png,
gc2.png
>
>
> There appears to be a GC issue due to memory pressure in the 0.6 branch.  You can see
this by starting the server and performing many inserts.  Quickly the jvm will consume most
of its heap, and pauses for stop-the-world GC will begin.  With verbose GC turned on, this
can be observed as follows:
> [GC [ParNew (promotion failed): 79703K->79703K(84544K), 0.0622980 secs][CMS[CMS-concurrent-mark:
3.678/5.031 secs] [Times: user=10.35 sys=4.22, real=5.03 secs]
>  (concurrent mode failure): 944529K->492222K(963392K), 2.8264480 secs] 990745K->492222K(1047936K),
2.8890500 secs] [Times: user=2.90 sys=0.04, real=2.90 secs]
> After enough inserts (around 75-100 million) the server will GC storm and then OOM.
> jbellis and I narrowed this down to patch 0001 in CASSANDRA-724.  Switching LBQ with
ABQ made no difference, however using batch mode instead of periodic for the commitlog does
prevent the issue from occurring.  The attached screenshot shows the heap usage in jconsole
first when the issue is exhibiting, a restart, and then the same amount of inserts when it
does not.

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