Sunday, November 24, 2013

Troubleshoot Large objects allocation in websphere

In gc logs you may find a line like below
<af type="nursery" id="2233" timestamp="Sep 24 09:20:52 2013" intervalms="24.176">
  <minimum requested_bytes="3660242" />

From the above line we understand that a large object allocation request was made and we are interested in finding what that object would be.

In google just put the line 3660242bytes to mb to find how much exact  mb is allocated.

There is a jvm argument options available to find the large objects.
-Xdump:stack:events=allocation,filter=#3m

 -Xdump option to add and remove dump agents for various JVM events, update default dump settings (such as the dump name), and limit the number of dumps that are produced.

Here we have given stack so stack trace will be dumped when allocation events is done above 3megabytes

Restart the server after the parameter is added and you will get stack trace in native_stderr logs whenever  a large allocation of more than 3 mb is done.



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