powered by Jive Software

Clearing up the JVM heap size stuff

The Installation Documentation on JVM heap size confused me for a little bit, and I wanted to see if you guys could clarify the docs at some point. Somehow while watching the forums and reading the Install docs I got the impression that the Linux JVM didn’‘t need to have it’'s heap size adjusted manually, when in fact it does.

So, I’'m requesting that the Custom Parameters section in the Install docs be split off or that a clearer explanation of the JVM heap settings be provided so that it accurately reflects the need for Linux admins to tune the JVM heap as well.

It might also be helpful to warn users not to create an unnecessarily large heap size so that the GC won’'t have to work harder than it needs to. I found the following pages helpful in looking into this heap stuff:

http://e-docs.bea.com/wls/docs81/perform/JVMTuning.html

http://java.sun.com/docs/hotspot/PerformanceFAQ.html

Thanks

Cameron

Cameron,

Actually, under JDK 1.5 the heap should just “do the right thing” in most cases. For example, it will automatically set the max size to 1GB or 1/4 RAM, whichever is smaller. Howerver, I agree that the docs could be clearer about everything. We’'ll try to make some improvements in a future release.

Thanks,

Matt

Hmm…I’‘ve got a Linux server (RHEL3) with 512MB of RAM. Using JM 2.1.3 from RPM (which includes JVM 1.5). If the JVM chose 1/4 RAM, it should go with 128MB, but it’'s starts with only 64MB. ??

Anyway, regardless of what the JVM may or may not do automagically, it would probably be a good idea (for me, at least) to explicitly set the heap size to keep out of trouble.

Thanks for your help, Matt.