Best Practice: Being too aggressive with your WLM policy can degrade WebSphere Application Server for z/OS performance
 Technote (troubleshooting)
 
Problem(Abstract)
If the goals set within Workload Mananger (WLM) on z/OS® are too aggressive, poor performance may result. This technote describes the current Best Practice for classifying WebSphere® Application Server work in WLM.
 
Cause
If WLM is confronted with a goal that is impossible to meet then WLM will bypass the goal in favor of the rest of the z/OS system. If WLM attempts to meet an impossible goal the entire system could suffer in an attempt to satisfy one portion of the total work.
 
Resolving the problem
The following describes the different types of work when running WebSphere Application Server on z/OS:
1) The address spaces need enough resource to start and process normal operating system functions. Start up is important and an aggressive Velocity goal or SYSSTC setting is recommended. Typically, the address spaces are given a minimum of importance=2 and velocity=60 (relative to the rest of your velocity goals this should be high).

2) For Garbage Collection and JSP™ compiles at run time the address spaces should be placed into an aggressive STC classification. Typically, the address spaces are given a minimum importance=2 and velocity= 60 (relative to the rest of your velocity goals this should be high).

3) The Post Installer shell script and any other USS® utility running from a submitted job will use BPXBATCH. For automatically running the post installer, classify BPXBATCH using the OMVS classification rules within your WLM policy. If BPXBATCH work defaults to discretionary, shell scripts executed from a z/OS job will most likely run slow.

4) J2EE application work is run under the CB workload and should be given a Response Time with Percentile goal. Percentage response time goal is recommended. You should make your goals achievable.
Example: Goals that have 80% of the work that will complete in .25 seconds is a typical goal.
The recommendation for Response Time with Percentile goal should not be more aggressive than 90% of the work in .25 seconds. If you choose 99% of the work, then WLM will determine that an impossible goal is set and sacrifice it for the rest of the system. The same holds true if you choose .1 second . The same sacrifice may be chosen on an already constrained system.

Provide a high velocity default service class for CB transactions (the default is SYSOTHER). SYSOTHER will most likely be running at Discretionary, which will provide a poor performing result for WebSphere Application Server application work. Classify your work based on server name, server instance name, User ID and transaction class.
Velocity goals for application work are not meaningful and should be avoided.

5) If WebSphere Application Server depends on another sub-system like DB2®, CICS®, WebSphere MQ® or any other loosely coupled server, it is important to make the goals for all subsystems realistic. If the goals for IMS® work are 50% of the work in 3 minutes and the goal for WebSphere Application Server is 75% of the work in 3 seconds, WebSphere Application Server will wait for processing from IMS and WLM will not make the goal for WebSphere Application Server.

Finally, the WLM system programmer must work closely with the WebSphere Application Server programmer. Communication is vital to having an adequately performing system.
The following are links to these topics in the WebSphere Application Server for z/OS Information Center. These links will provide additional information for configuring WLM to accommodate WebSphere Application Server on z/OS:

http://publib.boulder.ibm.com/infocenter/ws51help/index.jsp?topic=/com.ibm.websphere.zseries.doc/info/zseries/ae/rprf_tunezwlm.html

and

http://publib.boulder.ibm.com/infocenter/ws51help/index.jsp?topic=/com.ibm.websphere.wbifz.doc/info/wbifz/ae/tins_postinstallapp.html
 
 
 


Document Information


Current web document: swg21179971.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 #: 1179971
IBM Group: Software Group
Modified date: Oct 15, 2004