JVM job for Tomcat taking lots and lots of CPU -- JAVA400-L

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Ladies and Gentlemen:

We have a customer installation in which the JVM job for our Tomcat server is frequently using massive amounts of CPU.

It is running in a subsystem with a private pool The private pool (5) is currently showing fewer page-faults in WRKSYSSTS than the base pool.

1 3052.92 1789.92 +++++ .0 .0 .0 .0
2 47586.35 264.65 621 11.2 979.9 377.4 1224.3
3 649.51 .00 13 .0 .0 .0 .0
4 6495.19 .00 1215 .1 .8 .8 1.6
5 7168.00 2.32 500 .0 .0 3.3 6.2

GC information on the JVM job shows:

Garbage collected heap: Initial heap size . . . . . . . . . : 3096.000M
Maximum heap size . . . . . . . . . : 5120.000M
Current heap size . . . . . . . . . : 4458.562M
Heap in use . . . . . . . . . . . . : 1907.673M
Other memory: Internal (break) memory size . . . . : 504.982M
JIT memory size . . . . . . . . . . : 74.000M
Shared classes memory size . . . . . : 0.000M
General GC information: Current GC cycle . . . . . . . . . . : 2184
GC policy type . . . . . . . . . . . : GENCON
Current GC cycle time . . . . . . . : 552
Accumulated GC time . . . . . . . . : 5108241

The job is currently running in Java 7, on a V7R3 box, with -Xms3096m and -Xmx5120m JVM arguments.

Would switching to Java 8 help? What are the maximum meaningful -Xms and -Xmx values for Java 7 and Java 8, respectively?

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