WebSphere Application Server & Liberty

WebSphere Application Server & Liberty

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  • 1.  how much can increase heap memory for WAS BASE -64 Bit (MIN & MAX ) for JVM

    Posted Mon August 03, 2020 09:02 AM
    Hello Team,

    How much increase  Max  heap memory on JVM on IBM WebSphere Application server -Base -7.0.0.45.

    Please find below details :

    OS name : Linux OS
    OS bit :64-bit
    OS version :RHEL 5.11 (Tikanga)

    IBM WebSphere Application Server -7.0.0.45(BASE):
    java :JRE 1.6.0
    WAS BIT:64-bit

    waiting for your reply . Please share the details JVM max memory details .
    Regards ,
    Panchajanya

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    Panchajanya Learning student
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  • 2.  RE: how much can increase heap memory for WAS BASE -64 Bit (MIN & MAX ) for JVM

    Posted Mon August 03, 2020 09:41 AM
    By default, WebSphere enables compressed references.  The maximum heap allowed with compressed references is 32GB.  You can disable compressed references and essentially use any amount of memory you want two.  However, since compressed references turn 64bit object references into 32bit object references and references make up a significant portion of most heaps, your actual memory usage will increase significantly if you disable compressed references.  Articles I have seen indicate up to a 70% increase on memory usage. 

    Regards,
    Dennis Riddlemoser

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    Dennis Riddlemoser
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    Original Message


  • 3.  RE: how much can increase heap memory for WAS BASE -64 Bit (MIN & MAX ) for JVM

    Posted Mon August 03, 2020 11:56 PM
    Thank you for your valuable information.

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    Panchajanya Learning student
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    Original Message


  • 4.  RE: how much can increase heap memory for WAS BASE -64 Bit (MIN & MAX ) for JVM

    Posted Tue August 04, 2020 10:01 AM
    Dennis, you are correct although one minor correction is that newer versions of J9 have increased the compressed reference capability to up to 57GB: https://www.ibm.com/support/knowledgecenter/en/SSYKE2_8.0.0/openj9/xcompressedrefs/index.html

    More generally, Panchajanya, note that there are other factors to increasing the heap size. You want to make sure you have enough RAM so that you're not paging, and as you increase -Xmx, your worst case pause time may increase so you should consider other GC policies like balanced over ~10GB, and other factors. Make sure to enable verbosegc and track the proportion of time in GC and make sure it's below ~5%: https://publib.boulder.ibm.com/httpserv/cookbook/Major_Tools-Garbage_Collection_and_Memory_Visualizer_GCMV.html#Major_Tools-Garbage_Collection_and_Memory_Visualizer_GCMV-Analysis

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    Kevin Grigorenko
    WebSphere SWAT
    IBM
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    Original Message


  • 5.  RE: how much can increase heap memory for WAS BASE -64 Bit (MIN & MAX ) for JVM

    Posted Tue August 04, 2020 04:36 AM
    Hello Panchajanya,
    what's the background of your question? Why do you want to consider increasing the heap? As this is an old WebSphere installation I guess that the applications worked well for a while - right? What changed? More users? New version of the application?

    @Dennis Riddlemoser explained some technical limits in the IBM JVM and things to consider when disabling compressed references. I.e. it is important to consider that you don't exceed the systems physical memory. Keep in mind that a system running Java applications should never swap as this kills performance (GC has to swap in all pages from the disk).  Also keep in mind that a larger heap is not always resulting in better performance.
    I'd suggest to enable verbose GC logging and analyze the data using GCMV to get a better understanding of the heap usage over time. If you are running OOM get a javacore or a system dump and use Memory Analyzer Tool to analze the dump. If you feel that the increased heap utilization is justified increase the heap in reasonable junks (best would be to use load testing to recreate the situation and then model the increase using load testing).
    ​

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    Hermann Huebler
    2innovate IT Consulting GmbH
    Vienna
    Austria

    #IBMChampion
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    Original Message


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