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From "Shawn Heisey" <s...@elyograg.org>
Subject RE: Permanently Full Old Generation...
Date Thu, 29 Nov 2012 15:28:50 GMT
> My jvm settings:
>
>
> -Xmx8192M -Xms8192M -XX:+CMSScavengeBeforeRemark -XX:NewRatio=2
> -XX:+CMSParallelRemarkEnabled -XX:+UseParNewGC -XX:+UseConcMarkSweepGC
> -XX:+AggressiveOpts -XX:CMSInitiatingOccupancyFraction=70
> -XX:+UseCMSInitiatingOccupancyOnly -XX:-CMSIncrementalPacing
> -XX:CMSIncrementalDutyCycle=75
>
> I turned off IncrementalPacing, and enabled
> CMSInitiatingOccupancyFraction,
> after issues with nodes being reported as down due to large Garbage
> collection pauses.  The problem with the memory profile was visible before
> the drop down to 1.2GB (this was when I reloaded the core), my concern was
> that the collection of the old generation didn't seem to free any of the
> heap, and we went from occasionally collecting to always collecting the
> old
> gen.
>
> Please see the attached gc log.

I am on the train for my morning commute, so I have some time, but no
access to the log or graph.

Confession time: GC logs make me go glassy eyed and babble incoherently,
but I did take a look at it. I saw 18 CMS collections and three entries
near the end that saif Full GC. It looks like these collections take 6 to
8 seconds. That is pretty nasty, but probably unavoidable, so the goal is
to make them happen extremely infrequently - do young generation
collections instead.

The thing that seems to make GC less of a problem for solr is maximizing
the young generation memory pool. Based on the available info, I would
start with making NewRatio 1 instead of 2.  This will increase the eden
size and decrease the old gen size. You may even want to use an explicit
-Xmn of 6144.  If that doesn't help, you might actually need 6GB or so of
old gen heap, so try increasing the overall heap size to 9 or 10 GB and
going back to a NewRatio of 2.

Thanks,
Shawn



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