Question

What is the Max heap size we can allocate ofr JVM for WAS 6.0.2.31

Asked by: dipinci

What could be the maximum heap size we can configure for a JVM  on WAS 6.0.2.31 on AIX 64 bit and 32 bit platform

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Asked On
2009-01-28 at 22:55:33ID24093692
Tags

WebSphere 6.0.2.31

Topics

Java Native Interface (JNI)

,

WebSphere Studio

,

IBM Websphere Application Server

,

IBM AIX Unix

,

Unix Operating Systems

Participating Experts
2
Points
125
Comments
12

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Answers

 

by: HonorGodPosted on 2009-01-30 at 11:37:19ID: 23511992

Simple answer is "it depends"..

For a 32 bit environment, the theoretical maximum is 2GB.
However, it depends upon how many shared pages are
being used, and by what "other" products installed on
the system.  For example, WebSphere MQ tends to grab
a bunch of these pages, which means that they will be
unavailable for the Application Server.

I'm still looking for information about the 64 bit environment

 

by: HonorGodPosted on 2009-01-30 at 11:43:44ID: 23512060

For example, here is an IBM page that talks about MQ and the use of shared pages on AIX

http://www.IBM.com/support/docview.wss?rs=171&uid=swg21298595

 

by: HonorGodPosted on 2009-01-30 at 11:44:31ID: 23512071

If you have products like MQ that consume these limited shared pages, then this space will not be available for the WebSphere Application Server process(es).

 

by: dipinciPosted on 2009-01-31 at 01:39:30ID: 23516074

There is no MQ running on this server. Only WebSphere Application Server running on this.

How paging is related to alocating JVM heap size to the Application Server?

 

by: HonorGodPosted on 2009-01-31 at 06:53:26ID: 23516963

Well, when the Application Server is sending data, there are times that large data must be copied from the Java heap to native memory in order for the TCP/IP stack
to access and reliably send/receive this data.  This native memory is kept in the
shared pages.

 

by: dipinciPosted on 2009-01-31 at 11:35:28ID: 23518186

Okay. So what could be the max heap size we can allocate for a WAS JVM on 64 bit if only WAS is running on the AIX server with 8GB of RAM.

 

by: gheistPosted on 2009-01-31 at 13:51:02ID: 23518722

Address space is 1 EB subject to our swap space.

 

by: HonorGodPosted on 2009-02-02 at 06:00:39ID: 23526904

The real answer is "it depends".  Even with WAS being the only "significant" application, they way, and number of applications that you have deployed on the Application Server, and how many of them can actually be executing concurrently
can greatly affect the performance of WebSphere, and the Operating system.

Generally, it is best to have the minHeap size be set "relatively" low.  In your case,
I would recommend starting with 1GB, and probably setting the max to be 1/2 your
physical memory (i.e., 4GB).  Then, test, test, and test some more, to see how your
application, and the application server actually perform with these settings.

Use vmstat and tools like the "IBM Thread and Monitor Dump Analyzer" that are
available from http://www.alphaworks.ibm.com/tech/jca

You might also want to use something like the "HeapAnalyzer", which is available
from http://www.alphaworks.ibm.com/tech/heapanalyzer to make sure that your
application doesn't have some kind of memory leak.  If it does, having a large
maxHeapSize can make the leak that much harder to find.

 

by: gheistPosted on 2009-02-02 at 06:38:26ID: 23527217

And one should not set heap maximum to more than 3/4 of main memory. AIX can accomodate routine paging with some config tricks, but this is not intended way to work.
Basically - keep heap maximum below system RAM, thruput GC type is less intrusive.
When you get OOM increase and add RAM

If you get into paging speed will drom 10..100 times depending on vm subsystem tuning.
For 32bit AIX you have to set environment variables to get up from default 256M*11 to 256*15 and more

 

by: HonorGodPosted on 2009-02-06 at 03:36:07ID: 23568743

Thanks for the grade & points.  Good luck & have a great day

20120131-EE-VQP-002

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