This is expected behaviour. The heap will not grow if the memory required can 
be gained through a garbage collection. The heap will only grow if after a 
garbage collection it still cannot allocate the required memory or is over a 
certain percentage (I forget what the default is).

I would suggest that you don't in fact need 512MB if your app runs fine with no 
OOM in 512MB.

If you really want to use the full 1GB the you'll have to use -Xms as you 
suggested.

Ta
Matt

-----Original Message-----
From: Guillaume Lahitette [mailto:[EMAIL PROTECTED]
Sent: 20 April 2005 13:54
To: tomcat-user@jakarta.apache.org
Subject: Heap not expanding beyond -Xms512m


Hello Tomcat-oids,

I'd really appreciate any help with this...Thanks in advance.

We've been running performance tests against Tomcat 4.1.26 on Linux and 
Windows. We've tuned heap sizes to -Xms512m -Xmx1024m.
 
Monitoring the JVM memory usage with a daemon thread calling 
Runtime.getRuntime().freeMemory() / totalMemory() / maxMemory(), we've noticed 
memory was never expanded beyond 512MB. Instead, when usage was getting close 
to 512MB, we could see the garbage collector kick in. We never got OOM errors.
 
Can anyone share experiences about this? Do I have to use -Xms1024m -Xmx1024m 
(which seems to defeat the purpose of having ms and mx...)?

Guillaume

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