[Deploying Sakai] JVM GC tuning for Java 1.6

Robert Cohen robert.cohen at anu.edu.au
Thu Aug 19 23:07:23 PDT 2010

Yeah, I get the impression that GC tuning is definitely a black art.

We're using 

-server -Xms1500m -Xmx1500m  -XX:MaxPermSize=512m -XX:PermSize=512m
-XX:+UseParallelGC -XX:GCTimeRatio=49 -verbose:gc -XX:+PrintGCTimeStamps

and while I don't suggest its a definitive benchmark, using those settings
on our test server I get a tomcat startup time of 86 sec.

Whereas with something similar to your settings I see a startup time of
around 96 secs.

You can probably shave a couple of seconds off your startup time by adding

And UseParallelGC instead of ConcMarkSweep might be worth a try.

On 19/8/10 7:30 PM, "Stephen Marquard" <stephen.marquard at uct.ac.za> wrote:

> Hi all,
> I recently asked about GC settings for java 1.6, as our GC behaviour got
> significantly worse when we moved from 1.5 to 1.6.
> We've now updated our GC settings to:
> -server -d64 -Xms5000m -Xmx5000m -XX:MaxPermSize=512m -XX:+UseConcMarkSweepGC
> -XX:+ExplicitGCInvokesConcurrent -XX:+CMSIncrementalMode -verbose:gc
> -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
> with good results. We were previously using:
> -server -d64 -Xms5000m -Xmx5000m -Xmn1g -XX:MaxPermSize=512m -XX:+UseParNewGC
> -XX:+UseConcMarkSweepGC -XX:GCTimeRatio=19 -XX:SurvivorRatio=8
> -XX:TargetSurvivorRatio=90 -XX:MaxTenuringThreshold=31 -verbose:gc
> -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+DisableExplicitGC
> Regards
> Stephen
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Robert Cohen
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