Smart Plug-in for WebLogic Server Reference Guide

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Chapter 1
Metric B005_JVMMemUtilPct
Instruction Text The JVM is running out of available heap space.
Probable cause: The JVM heap size may be set too low for the client load.
Potential impact: The JVM heap size determines how often and how long the
VM spends collecting garbage (de-allocating unused Java objects). The Java
heap is where the objects of a Java program live. When an object can no longer
be reached from any pointer in the running program, the object is garbage.
Garbage collection affects performance because JVM work cannot proceed
during full garbage collection. An acceptable rate for garbage collection is
application specific and should be adjusted after analyzing the actual time and
frequency of garbage collections.
The goal of tuning your heap size is to minimize the time that you spend doing
garbage collection while maximizing the number of clients that you can handle
at a given time.
If you set a large heap size, full garbage collection is slower, but it occurs less
frequently. For a smaller heap size, full garbage collection is faster, but occurs
more frequently.
Suggested action: For additional information on tuning your heap size, see the
'Performance and Tuning' documentation for your WebLogic Server version
available through http://e-docs.bea.com/.
You can set the heap size using the options -Xms and -Xmx on the Java
command line in the script used to start the server. Use the -Xms option to set
the minimum size of the heap. Set this value to a multiple of 1024 that is greater
than 1MB. Use the -Xmx option to set the maximum Java heap size. Set this
value to a multiple of 1024 that is greater than 1MB. As a general rule, set
minimum heap size equal to the maximum heap size. If you are using 1.3 Java
HotSpot JVM, also set generation sizes. Make sure that the heap size is not
larger than the available free RAM on your system. Use as large a heap size as
possible without causing your system to swap pages to disk. The amount of free
RAM on your system depends on your hardware configuration and the memory
requirements of running processes on your machine. See your system
administrator for help in determining the amount of free RAM on your system.
Typically, you should use 80% of the available RAM (not taken by the operating
system or other processes) for your JVM. If you find that you have a arge
amount of RAM remaining, run more WebLogic Servers on your machine.
Action/ASCII Report Yes
Area Performance
Monitor Template Name WLSSPI_0005