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From "Peter Crowther" <Peter.Crowt...@melandra.com>
Subject RE: Very Long Full GC after Inactivity
Date Tue, 09 Oct 2007 08:25:33 GMT
> From: Bill Clarke-Fields [mailto:wfields@dadebehring.com] 
> We are running an application on Tomcat 5.0.28 with Java 
> 1.4.2.  The usage
> of the application is very cyclical.  It is used heavily 
> during the day, and
> lightly at night.  During peak daytime hours, a full garbage 
> collection
> takes less than 2 seconds, which is fine.  However, after a 
> long period of
> inactivity in the evening, a full garbage collection will be 
> triggered and
> take a very long time.  Sometimes over a minute!

I suspect the app is being paged out overnight by other jobs.  Overnight
virus scans will do this on Windows, for example, as the disk cache
expands to fill available memory.

You could test this by running Performance Monitor (Windows) or your
preferred logging tool (UNIX) overnight in log mode and looking for high
page-in and disk I/O values around the time of the full GC.  For
preference, use the Process counters on Windows, as they'll tell you for
sure whether it's the Java process that's causing the paging traffic.

		- Peter

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