IBM 6.1.X manual server, XXMaxPermSize, XX+UseConcMarkSweepGC, XXSurvivorRatio, XX+UseParNewGC

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	Linux	Solaris	Windows	z/Linux	z/OS
	POWER5			2003
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.

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W E BS P HE R E P O R T AL V 6 . 1 T U N I N G G U I D E