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Message-ID: <4B6C43CA.4010200@christopherschultz.net>
Date: Fri, 05 Feb 2010 11:14:02 -0500
From: Christopher Schultz <chris@christopherschultz.net>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: Heap size rule for Tomcat 5.5
References: <27463924.post@talk.nabble.com>
In-Reply-To: <27463924.post@talk.nabble.com>
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Evebill8,

On 2/5/2010 1:08 AM, evebill8 wrote:
> I heard the rule to set the Tomcat's heap size is 2/3 of the memory.

I agree with Chuck: this sounds like malarkey. Whoever told you that
doesn't know what they're talking about.

The rule for any Java program is: set the heap to whatever you need to
properly run your program.

For instance, our production machine has a mere 2GiB of memory and our
main JVM (we run 3 simultaneously) is configured to run with a 192MiB
heap... much less than the "recommended" 1.3GiB heap you stated above.
Our webapp runs very lean in memory and we don't have so many
simultaneous users that we have tons and tons of sessions laying around.

> We are running Tomcat 5.5 on the 64-bit Linux.  The box has 16GB of
> RAM, and we just allocate 8GB to heap.

Do you even need that much? We only recently raised the heap size from
the default (in our environment) 64MiB heap, where it was running just
fine until our user load increased.

> If the rule is true, this means I can allow at
> least 10GB to Tomcat, and leave 6GB to the OS.

If there's nothing else running, the OS can certainly run comfortably in
6GiB of memory. Your OS ought to fit comfortable in a few /MiB/, let
alone a few GiB.

- -chris
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