Setting the BPX parameter VMAX too low can cause shell scripts to perform poorly
 Technote (troubleshooting)
 
Problem(Abstract)
VMAX defaults to half the available physical memory, if you explicitly set it too low the performance of shell scripts and some WebSphere® Application Server for z/OS® functions will be very slow.
 
Cause
From the Hierarchical File System Usage Guide Redbook at the following URL: http://www.redbooks.ibm.com/redbooks/pdfs/sg245482.pdf; you will find a description of the virtual MAX BPX parmlib parameter.

"The VIRTUAL(max) parameter specifies the maximum amount of virtual
storage (in megabytes) that HFS data and metadata buffers should use.
The default is 50% of real storage available to the system at HFS
initialization time."

This parameter in practical experience is not often set by the customer. The default being half of the physical memory at Unix System Services start up is usually a large enough amount to not notice any performance hits. Because of this lack of exposure and the processing of the VMAX parameter being all within buffers in memory, problems are difficult and time consuming to diagnose.

 
Resolving the problem
Take the default for VMAX or increase the value if shell utilities appear to be performing poorly.
 
 
 


Document Information


Current web document: swg21180409.html
Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server for z/OS > Hangs/Performance Degradation
Operating system(s): z/OS
Software version: 5.1
Software edition:
Reference #: 1180409
IBM Group: Software Group
Modified date: Sep 27, 2004