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Asked: 2026-05-21T23:24:13+00:00

Our application requires very huge memory since it deals with very large data. Hence

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Our application requires very huge memory since it deals with very large data. Hence we increased our max heap size to 12GB (-Xmx).

Following are the environment details

OS - Linux 2.6.18-164.11.1.el5    
JBoss - 5.0.0.GA
VM Version - 16.0-b13 Sun JVM
JDK - 1.6.0_18

We have above env & configuration in our QA & prod.
In QA we have max PS Old Gen (Heap memory) allocated as 8.67GB whereas in Prod it is just 8GB.

In Prod for a particular job Old Gen Heap reaches 8GB, hangs there and the web URL become inaccessible. Server is getting down.
But in QA also it reaches 8.67GB but full GC is performed and its coming back to 6.5GB or something. Here its not getting hanged.

We couldn’t figure out a solution for this because both the environment and configuration on both the boxes are same.

I have 3 questions here,

2/3rd of max heap will be allocated to
old/tenured gen. If that is the case
why it is 8GB in one place and 8.67GB
in another place?

How to provide a valid ratio for New
and Tenure in this case(12GB)?

Why it is full GCed in one place and
not in the other?

Any help would be really appreciable. Thanks.

Pls let me know if you need further details on env or conf.

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1 Answer

  1. Editorial Team

    For your specific questions:

    1. The default ratio between new and old generations can depend on the system and what the JVM determines will be best.
    2. To specify a specific ratio between new and old generations with -XX:NewRatio=3.
    3. If your JVM is hanging and the heap is full it’s probably stuck doing constant GC’s.

    It sounds like you need more memory for prod. If on QA the request finishes then perhaps that extra 0.67GB is all that it needs. That doesn’t seem to leave you much headroom though. Are you running the same test on QA as will happen on prod?

    Since you’re using 12GB you must be using 64-bit. You can save the memory overhead of 64-bit addressing by using the -XX:+UseCompressedOops option. It typically saves 40% memory, so your 12GB will go a lot further.

    Depending on what you’re doing the concurrent collector might be better as well, particularly to reduce long GC pause times. I’d recommend trying these options as I’ve found them to work well:

    -Xmx12g -XX:NewRatio=4 -XX:SurvivorRatio=8 -XX:+UseCompressedOops
-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+DisableExplicitGC
-XX:+UseCMSInitiatingOccupancyOnly -XX:+CMSClassUnloadingEnabled
-XX:+CMSScavengeBeforeRemark -XX:CMSInitiatingOccupancyFraction=68
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