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3 replies Latest Post - ‏2012-11-29T21:14:42Z by SystemAdmin
WiseMind
WiseMind
6 Posts
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Pinned topic Which IBM JVM is better 32 bit or 64 bit under 64bit OS

‏2012-11-28T11:17:15Z |
Hi,

Could you please tell me which IBM JVM is better 32 bit or 64 bit under 64bit OS?

Please advice with scenarios.

Thanks
Updated on 2012-11-29T21:14:42Z at 2012-11-29T21:14:42Z by SystemAdmin
  • SystemAdmin
    SystemAdmin
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    Re: Which IBM JVM is better 32 bit or 64 bit under 64bit OS

    ‏2012-11-28T11:31:50Z  in response to WiseMind
    It's not a case of which is better, it's a case of what you need.

    If you need a 64bit address space to get the size of heap you need for your application then you have no choice but to use the 64bit JRE.

    If on the other hand you don't need a large heap then the 32bit JRE will use less memory running the same application than the 64bit JRE because all the pointers will be shorter (and as a result the objects will be smaller).

    You can reduce some of this overhead by running with the -Xcompressedrefs command line option on the 64bit JRE but the 32bit JRE will still use less memory overall.

    Ben Hardill
    • WiseMind
      WiseMind
      6 Posts
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      Re: Which IBM JVM is better 32 bit or 64 bit under 64bit OS

      ‏2012-11-29T12:44:56Z  in response to SystemAdmin
      Thanks for your reply.

      Actually when we have to think that we need a larger heap size? As we can see most of the applications can run on 32bit JVM. What do you suggest which JVM is better if we have a larger application and 100 users need to access the applications at the same time. Or which parameters or scenarion make us think we should go for 64bit JVM.

      I know questions are basics but these questions mean to us.

      Thanks
      • SystemAdmin
        SystemAdmin
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        Re: Which IBM JVM is better 32 bit or 64 bit under 64bit OS

        ‏2012-11-29T21:14:42Z  in response to WiseMind
        The only real answer to you questions are "It depends".

        Without knowing what your application does and how it's written it's hard to say, but I would suggest that an "average" Web application with 100s of users would be fine in a 32bit JVM. But the only way to sure is to test the application with a known number of users and measure the heap size using verbose gc then add some more users and compare the increase in heap size to get an indication of how it will scale up to the max user numbers.

        32bit JVMs maximum heap size differ depending which OS you are running on, (1.8gb on 32bit Window, 3gb on AIX) and the basic rule of thumb is you should not use more than 70% of this after GC at maximum throughput. If your projections from above suggest you will need more than this then you will have to use the 64bit JVM