Tuning the DFSMStvs environment

In addition to improving sequential performance and logging, you can tune several things in the DFSMStvs environment to influence the performance. What you tune depends on the information you gained from performance monitoring, as Monitoring performance describes. The following list describes some things that you might want to tune:

Applications
If you detect that there is excessive lock contention or that the system logger is forced to spill active log records to disk, you might want to tune the commit frequency that you have implemented in an application program.
Coupling-facility storage
- SMSVSAM use
  If you see structure-full events for the SMSVSAM structures, you might want to change the amount of storage in the coupling facility available for SMSVSAM.
- System logger use
  If you see structure-full events for the logger structures, you might want to change the amount of storage within the coupling facility available to the system logger.
  
  When a log becomes full and the system logger has to offload log data, the system logger starts surfacing temporary errors. While this occurs, it is impossible to write anything to the log.
DFSMStvs SMS settings
If you see many occurrences of a coupling facility log structure filling and spilling to disk, you might want to reduce the activity keypoint frequency. Setting the activity keypoint frequency too low, however, would increase the amount of processor time needed to trim logs.
Application parallelism
When you run multiple batch jobs against the same shared VSAM data sets, you can obtain benefits by rescheduling existing jobs. You can take advantage of application parallelism still further by taking existing jobs and splitting them into multiple parallel jobs. This reduces the overall run time substantially, depending on how many ways you split a single job. A shorter run time does, however, mean that the total amount of resources consumed by the job is now consumed in a shorter period of time, so creating more parallel jobs can cause a peak in processor use and I/O demand.

Recommendation: Improve performance by setting up your z/OS® system optimally in these ways:

Run DFSMStvs batch and CICS® from separate z/OS images rather than combining the two within one z/OS image.
Place a couple data sets and JES2 checkpoint on different volumes.
Place the primary sysplex CDS and the coupling facility resource management (CFRM) CDS on different volumes.
Ideally, spread the primary and alternate couple data sets and the CFRM data sets across four volumes.
Give SMSVSAM a higher dispatching priority than VTAM® and CICSPlex® System Manager, which in turn should have a higher dispatching priority than CICS. When you run in goal mode, however, you should allow these system address spaces to default to SYSTEM/SYSSTC.
As a starting point, set the activity keypoint to 5000.
Use GRS star mode.
Define only the number of systems that will actually join the sysplex in a couple data set MAXSYSTEM value.
The RLS lock structure, IGWLOCK00, bases the size of each lock entry on the number of systems permitted to join the sysplex. Each lock entry increases in size as more systems are defined. If you define more systems in the couple data set MAXSYSTEM value than will actually join, each record is larger than necessary and you can fit fewer records in a given amount of coupling facility space.
Increase the size of your lock structure (IGWLOCK00). DFSMStvs introduces additional locking because batch jobs do not hold locks in today's processing environment.