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From Ronald Klop <ronald-mailingl...@base.nl>
Subject Re: Does GC Really Matter (Is This Situation)?
Date Wed, 23 Jun 2010 11:02:17 GMT



Op dinsdag, 22 juni 2010 18:33 schreef "Robinson, Eric" <eric.robinson@psmnv.com>:
> 
>  
> This is a similar question to one already being discussed in the list
> with the subject "Setting the Right Amount of Memory".
> 
> We have 160 instances of tomcat on the same server, with most instances
> configured to use 64-96MB of RAM. We carefully watch the logs for OOMEs.
> If we see any, we increase the RAM allocation for that instance by 32MB,
> which is enough to make the OOMEs go away.
> 
> Some people say this approach will lead to increased CPU utilization
> from frequent GC; however, our server runs 90% idle all day long so CPU
> is evidently not being driven up by much, if any. 
> 
> Given the circumstances, is there anything to be gained from increasing
> the heap size? Our software vendor wants us to increase each tomcat
> instance to 512MB, just as a matter of policy, but I don't see a good
> technical reason to do that. 
> 
> Am I missing something?
> 
> --
> Eric Robinson
> 
> 
> 
> 

You can monitor the gc with jstat.
jstat -gc <pid> 10s
This wil show you the memory usage of a java instance with the time spent in GC. If it does
0.9 sec. of GC every sec. you are running inefficient. :-)

Ronald.



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