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From Peter Crowther <>
Subject Re: Heap size rule for Tomcat 5.5
Date Sat, 06 Feb 2010 10:41:59 GMT
On 5 February 2010 18:05, evebill8 <> wrote:

> Cool!  I just want to confirm if the rule is right.  My IT guy also does
> not
> believe it.
> It wasn't a bad rule of thumb as a place from which to start tuning when
typical server memory sizes were 0.5G to 2G - it reserved "sort-of enough"
RAM for the OS and the non-heap parts of Java and "sort-of enough" RAM for
the web application, though as you can imagine that varied quite a lot.  But
it could never really be said to be optimal, and ideally you'd always
measure and tune.

These days, there's so much more RAM in most servers that tuning becomes
more relevant if the load's high.  If your application is very heavy on disk
reads, for example, you might do better to reduce its heap size in order to
give the OS more space to cache disk pages.  By contrast, I have one *very*
heavy compute application (not directly a web app) that likes all the RAM it
can get as heap memory to cache intermediate results in case they can be

- Peter

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