WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

For more information about how to convert applications to run in 64-bit mode,
see the following resources:
► IBM Whitepaper WP101095 C/C++ Code Considerations With 64-bit
WebSphere Application Server for z/OS, available at the following Web page:
http://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/WP101095
► Language Environment Programming Guide for 64-bit Virtual Addressing
Mode, SA22-7569
Bigger heap needed for applications
Simply using the 64-bit addressing mode does not mean that the sizes for the
various heaps need to be increased.
In general, good minimum and maximum heap sizes should be identified by a
verbose garbage collection (GC) analysis. This technique will allow you to
identify these values, thereby reducing the GC overhead and saving CPU time. It
is suggested to perform a verbose GC analysis on a regular basis, especially if
the number of users or the amount of transactions has changed.
For more information about how to perform a verbose GC analysis refer to the
Information Center article Tuning the IBM virtual machine for Java, available at
the following Web page:
http://publib.boulder.ibm.com/infocenter/wasinfo/v7r0//topic/com.ibm.we
bsphere.zseries.doc/info/zseries/ae/tprf_tunejvm_v61.html
Note: In general the structure of the WebSphere Application Server for z/OS
will significantly reduce the maximum heap size compared to the maximum
heap sizes used on the distributed platforms.
For more information about how this is achieved see 14.1.5, “Runtime
processes” on page 425.
500 WebSphere Application Server V7.0: Concepts, Planning, and Design