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Subject: Re: Memory usage increased form 500MB to 4 GB after changing the
 tomcat process from 32 bit to 64 bit execution
To: users@tomcat.apache.org
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From: =?UTF-8?Q?Andr=c3=a9_Warnier_=28tomcat=29?= <aw@ice-sa.com>
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Date: Fri, 14 Apr 2017 12:06:28 +0200
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archived-at: Fri, 14 Apr 2017 10:06:16 -0000

On 14.04.2017 10:36, nagendra.raju@wipro.com wrote:
> Hi All,
> Problem statement: Memory usage increased form 500MB to 4 GB after changing the tomcat process from 32 bit to 64 bit execution
> As tomcat memory has increased it is impacting available memory for other applications on server
>
> o   Is this a bug ?
>
> o   Earlier with 32bit it was running around 400MG, If we restrict the tomcat memory to 500GB for 64bit application will  it any impact on tomcat operations
>
> Tomcat Version : Tomcat 7.0.73 on Solaris 11
>

Maybe as a very first observation : it is not Tomcat that you changed. The Tomcat code has 
remained exactly the same. It is the Java JVM that was changed, from a 32-bit to a 64-bit 
version. So /that/ is the underlying reason for the memory usage increase, not Tomcat.
Read more on the topic : http://lmgtfy.com/?q=java+32-bit+vs+64-bit

(I recommend this one as a starter : 
http://howtodoinjava.com/for-fun-only/difference-between-32-bit-java-vs-64-bit-java/)

Thus, to respond to your first question : no, it is no a bug; or at least not a Tomcat bug.
About your second question : there is no such thing as a 64-bit application under Tomcat. 
All Tomcat applications are written in Java, and are ultimately run by the Java JVM. It is 
the JVM which determines if this uses, for example, 32-bit or 64-bit memory pointers, 
4-byte or 8-byte object references etc.
If you reduce the available memory for the Tomcat Heap, then, depending on the way the 
applications are written, this may cause more Memory Garbage Collections to occur in any 
given period of time.  Whether this really impacts your applications or not, is something 
which only you can measure and determine.
Try it, and look at the results.
Or add more memory to your server.
If you went from a 32-bit JVM to a 64-bit JVM, presumably you had a reason for doing that. 
Wat was the reason ? (And if there was no good reason, you can always go back).


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