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From David kerber <dcker...@verizon.net>
Subject Re: tomcat6 -minheap,maxheap size
Date Wed, 23 Mar 2016 13:49:15 GMT
On 3/23/2016 9:19 AM, Christopher Schultz wrote:
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> David,
>
> On 3/23/16 8:02 AM, David kerber wrote:
>> On 3/23/2016 3:36 AM, Mahudeswaran A wrote:
>>> Hello All, Is there any recommended maximum setting for tomcat-6
>>> 32bit version running on windows 64bit OS
>>
>> No, there is not.  It all depends on your app's requirements.  I
>> have applications for which 64MB is plenty, and others which need
>> 1024MB.  I think the max on 32-bit is 2048MB (2GB), but I'm not
>> sure of that.
>
> Something like that, depending upon a few things. I think I wasn't
> able to get above 1520MiB on 32-bit Windows, but that's because of
> some weirdness the OS does with kernel-versus-process address space.
> Evidently, the process can have 32-bit pointers, but reserves *half*
> of that for kernel space. You used to be able to use some kind of boot
> parameter to set that kernel/process split to 3GiB/1GiB... not sure if
> that works anymore. It doesn't matter, though... everyone should be on
> 64-bit, now.
>
> If you are running on a 64-bit OS, it *generally* makes sense to use a
> 64-bit JVM, but I can see lots of reasons to use a 32-bit JVM - if you
> can get away with it - mostly memory-related.

We run 32-bit to simplify installations.  We have several non-java 
applications that are still 32-bit, and running 32-bit java lets us get 
away with installing only one set of db drivers and ODBC DSNs, which all 
applications (both java and non-java) can use.  None of them need 64-bit 
java just for memory requirements.


>
> 64-bit JVMs can use compressed object pointers (and they do by
> default) to take up less memory than if they used native pointers, but
> the reality is that a 64-bit JVM simply requires more memory than the
> same exact application running under a 32-bit JVM.
>
> If you can get away with less than ~2GiB of heap, then I would say
> stick with the 32-bit JVM. You can always move to 64-bit.
>
> Note that Tomcat itself is 100% Java and so there isn't really a
> "32-bit Tomcat" though it is packaged that way: the 32-bit package
> just has a 32-bit installer and is bundled with the 32-bit Windows
> service, a 32-bit tcnative, etc.
>
>>> We would like to change the default setting and looking for max
>>> size/count for 32bit tomcat-6 running on 64bit windows OS. Min
>>> heap size=? Max heap size=? Max Thread count=?
>
> IMO, you should only use as much memory as you actually need. Some
> people like allocating enormous heaps because "more is better", but I
> tend to think that if you have a huge heap, it will take you forever
> to notice any kinds of memory problems that you have.
>
> - -chris
>
> (Still very happily running in production with 512MiB heaps for our
> "biggest" web applications.)
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