Setting TSO options for threads

You can specify limits for the number of threads taken by the TSO and batch environments

Procedure

To tune your TSO attachment facility:

  • Specify values for the following subsystem parameters:
    IDFORE
    The maximum number of TSO foreground connections (including DB2I, QMF, and foreground applications)
    IDBACK
    The maximum number of TSO background connections (including batch jobs and utilities)
  • Because Db2 must be stopped to set new values, consider setting a higher IDBACK value for batch periods.
    The statistics record (IFCID 0001) provides information on the create thread queue. The IBM® OMEGAMON® for Db2 Performance Expert on z/OS® statistics report shows (as shown in the example below) that information under the SUBSYSTEM SERVICES section.

Example

For TSO or batch environments, having 1% of the requests queued is probably a good number to aim for by adjusting the value of the CTHREAD subsystem parameter. Queuing at create thread time is not desirable in the CICS® and IMS environments. If you are running IMS or CICS in the same Db2 subsystem as TSO and batch, use the values of the IDBACK and IDFORE subsystem parameters to limit the number of threads taken by the TSO and batch environments. The goal is to allow enough threads for CICS and IMS so that their threads do not queue. To determine the number of allied threads queued, see the QUEUED AT CREATE THREAD field ( A ) of the IBM OMEGAMON for Db2 Performance Expert on z/OS statistics report.

Figure 1. Thread queuing in the IBM OMEGAMON for Db2 Performance Expert on z/OS statistics report
SUBSYSTEM SERVICES           QUANTITY
---------------------------  --------
IDENTIFY                     30757.00
CREATE THREAD                30889.00
SIGNON                           0.00
TERMINATE                    61661.00
ROLLBACK                       644.00
 
COMMIT PHASE 1                   0.00
COMMIT PHASE 2                   0.00
READ ONLY COMMIT                 0.00
 
UNITS OF RECOVERY INDOUBT        0.00
UNITS OF REC.INDBT RESOLVED      0.00
 
SYNCHS(SINGLE PHASE COMMIT)  30265.00
QUEUED AT CREATE THREAD  A       0.00
SUBSYSTEM ALLIED MEMORY EOT      1.00
SUBSYSTEM ALLIED MEMORY EOM      0.00
SYSTEM EVENT CHECKPOINT          0.00