Identifying memory fragmentation | Tactic 2: Tune -Xk and -Xp to minimize fragmentation

Option 1: Tune max heap size to optimize GC frequency

Overview

If the free space after GC does not decline, check the GC cycle length and distribution, and the total GC pause time. If the time since the last AF in "GC cycle length and distribution" is not too small, but the complete time in "Total GC Pause Time" is high, it means that GC is not very frequent and GC duration is very high.

• If duration, not including compaction, exceeds 10 seconds, the heap is probably too large for the application and GC takes a long time to clean up objects in this large heap, so reduce the maximum heap size.

• If GC frequency is too high, the heap is probably too small for the application and GC needs to run frequently, so increase the maximum heap size.

Set the JVM max heap size

1. Open the WebSphere Application Server administrative console

2. Expand...

   Servers | Application servers | server1 | Java and Process Management | Process Definition | Java Virtual Machine

3. Change the max heap size to a larger value.

4. Click Apply and click Save at the top of this page.

5. Restart WebSphere Application Server.

6. Try your test case again and see if the problem disappears.

i5/OSŪ should have no maximum heap size according to the System i Tuning Guide because the allocation model is different from other platforms. After it is set to unlimited, it may take a couple of days to stabilize at 3 GB.

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