IMS Contention During OM Deliver Pre-spool Processing

Products

• OM Deliver

Issue/Introduction

Resource contention between IMS regions and OM Deliver.

System log shows exclusive waits on QNAME SARUPD - SYSU.SARPRD1.SARDBASE.I000001

Contention cleared once started tasks recycled.

Environment

OM Deliver 14.0

Cause

The contention is typically caused by a combination of two configuration factors:

• Using JOBCLSL=* in the OM Deliver initialization parameters causes the pre-spool task to scan all output classes, including Started Tasks. This results in OM Deliver attempting to process all IMS Started Task output, leading to frequent and exclusive locks on the database index.
  
  
• By default, OM View and OM Deliver use hardware RESERVES for database serialization.
  
  
• The environment is using hardware RESERVES for database serialization, rather than global ENQs. Hardware reserves lock the entire volume, which significantly increases the likelihood of contention between the OM View/Deliver tasks and the IMS regions. In general the recommendation is to convert RESERVES to ENQs.
  
  
• This impact is primarily seen in pre-spool configurations where OM Deliver scans output prior to it reaching the JES spool.

 

Resolution

• Restrict job classes
  • Modify the JOBCLSL initialization parameter to exclude Started Tasks.
  • Instead of using the wildcard (*), specify only the specific batch job classes required for OM Deliver processing.
  • Note '@' represents TSO sessions and '$' represents Started Tasks - refer JOBCLSL Initialization Parameter
    
    
• Serialization
  • Configure your system to convert hardware RESERVES to global ENQs. This allows for more efficient serialization across the sysplex.
    
    
• Performance Tuning
  • Increase the SARBUFC parameter in the View initialization parameters. A recommended starting value is 64 or 100 (default is often 10).

Additional Information

Note: This issue is unique to OM Deliver in pre-spool configuration.

Set up for Multiple CPUs