IBM WEBSPHERE 6.1.X User Manual
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W E B S P H E R E P O R T A L V 6 . 1 T U N I N G G U I D E
J V M H E A P N E W A R E A S I Z E
The Generational Garbage Collector introduced in Java 5.0 is efficient to Portal application JVM
memory management, and it is set as default by installation with the –Xgcpolicy:gencon command-
line option. Use –Xmn to further fine tune the Java heap new area (Nursery).
The –Xgcpolicy:gencon option does not apply to Solaris.
How To Set: In the WebSphere Administrative Console: Servers
Application Servers
WebSphere Portal
Server Infrastructure: Java and Process Management Process Definition
Java Virtual Machine -> Generic JVM Arguments:–Xmn256m
Parameter
AIX
POWER5
Linux
Solaris
Windows
2003
z/Linux
z/OS
New Area Size -Xmn320m -Xmn256m
-Xmn768m -Xmn256m -Xmn1024m
-Xmn320m
A D D I T I O N A L S U N J V M A R G U M E N T S
On the Solaris platform, we use the following Java HotSpot parameters to achieve optimum
performance.
Table 1: Additional Sun JVM Settings
Parameter
Value
Additional Information
-server
Offers higher throughput than the "client" mode.
-XX:MaxPermSize
768m
-XX:+UseConcMarkSweepGC
Use concurrent mark-sweep collection for the tenured
generation. The application is paused for short periods
during the collection; we found this collector works best
in Portal.
-XX:SurvivorRatio
6
-XX:+UseParNewGC
By default concurrent low pause collector uses the
default, single threaded young generation copying
collector. Set this parameter to use parallel young
generation collector for new area.
-XX:ParallelGCThreads
5
Reduces the number of garbage threads. On the Chip
multithreading processor based system, we set the
threads no higher than one quarter of the hardware
threads. We also distribute the threads for 6 JVMs. Our
system has 128 virtual processors, we set a total of
(128/4)=32 GC threads across all the JVMs. So 5 or 6
GC threads per JVM.
-XX:+PrintGCDetails
Print more details at garbage collection. This does not
improve performance, but it provides additional
information related to garbage collection activity, which
is useful in tuning garbage collection.
-XX:+PrintGCTimeStamps
Print timestamps at garbage collection. See above.