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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Out of Memory Errors when upgrading from 5.0.27 to 6.0.14
Date Tue, 05 Feb 2008 15:33:47 GMT
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Dan,

(While others are handling your primary question, I thought I'd mention
a couple of things)

Dan D. wrote:
| I'm currently working on upgrading our systems from using Tomcat
| 5.0.27 to 6.0.14.

While you're at it, you might want to:

* If you're running a 64-bit OS, upgrade to a 64-bit JVM.
~  Without this, your 6GB -> 8GB memory upgrade isn't going
~  to give your Java process any more memory, since the 32-bit
~  JVMs can only give you about 2GB of useful heap.

* Consider running fewer application per JVM. Are you really running
~  ~1500 applications per Tomcat instance? That seems like quite a lot
~  (though by no means should it be considered impossible!)

| The output from jmap seems to show that the majority of the
| heap/memory is being consumed by character arrays.

This is not surprising. Java uses a lot of String objects internally for
lots of stuff (like package, class, and method names, for instance) and
every single one of them is backed by a character array.

Don't read too much into the fact that character arrays take up a lot of
space, because they can be allocated in all kinds of ways that are not
related to the "character array" itself.

What you really want to do is run a profiler to find out where many of
the character arrays were created in the first place.

Good luck,
- -chris
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