Removing idle tpipes

IMS scans transaction pipes (tpipes) during system checkpoint processing to determine if any tpipes can be deleted.

IMS removes transaction pipes after they have been idle for three consecutive system checkpoints, except in the following circumstances:
  • Commit-then-send messages are queued on the tpipe or the tpipe hold queue.
  • The tpipe is stopped.
  • A trace is set on the tpipe.
  • The tpipe is a synchronized tpipe, such as a tpipe used by MQSeries® for commit-then-send input transactions.
  • The tpipe is in a WAIT state for a resume tpipe request that specified either the AUTO or the SINGLE-WAIT options.
  • The tpipe is in an MCP state, which indicates that the tpipe is running in a shared queues environment and might have output messages on the global queue.
    Tip: If no messages are queued to the TPIPE but the MCP status is displayed for the TPIPE so that the tpipe cannot be removed, issue the /DISPLAY TMEMBER tmembername TPIPE tpipename QCNT command or the /DISPLAY TMEMBER tmembername QCNT command to reset the MCP status.
  • The tpipe is being scanned by IMS.

You can use the /DISPLAY TMEMBER TPIPE command to see whether a tpipe cannot be removed by IMS because one of the circumstances in the preceding list is true for the tpipe.

If IMS cannot remove a tpipe that has been idle across three consecutive checkpoints because one of the circumstances in the preceding list is true, IMS attempts to remove the idle tpipe again at the following system checkpoint.

You can view information about OTMA clients, OTMA tpipe connections, and the OTMA messages that are currently being processed by IMS by issuing the type-2 IMS command QUERY OTMATI.

Increasing tpipe cleanup frequency by using the FASTTPCU function

You can enable the fast transaction pipe checkpoint cleanup (FASTTPCU) function by specifying FASTTPCU=YES in the DFSOTMA descriptor in the DFSYDTx IMS.PROCLIB member. When this function is enabled, the IMS system can delete an idle OTMA tpipe more frequently. A tpipe that has been idle for two consecutive system checkpoints will be cleaned up. If the function is disabled or not specified, the IMS system uses the default tpipe cleanup. The IMS system cleans up a tpipe that has been idle for three consecutive system checkpoints instead.

The FASTTPCU settings in a shared queues environment

In a shared queues environment, if you activate the FASTTPCU parameter in the front-end IMS system, the behavior could vary in the back-end IMS system. Because the FASTTPCU parameter applies only to IMS 15.3 and later versions, the number of checkpoints for removing idle tpipes could be different depending on:
  • the versions of the front-end IMS system and the back-end IMS system
  • the installation of APAR PH52141 in the back-end IMS system

If both the front-end IMS system and the back-end IMS system are in IMS 15.3, and the back-end IMS system has APAR PH52141 applied, the back-end IMS system inherits the FASTTPCU setting from the front-end IMS system for any OTMA tpipes generate for the work from the front-end IMS system. This overwrites any FASTTPCU setting in the back-end IMS system.

If the back-end IMS system is in IMS 15.2 or lower versions, the following table provides information about how many checkpoints it takes to remove idle tpipes in a shared queues environment in different cases:
Table 1. The number of checkpoints for removing idle otma tpipes
  Front-end IMS system in IMS 15.2 or lower versions Front-end IMS system in IMS 15.3 or higher versions
Back-end IMS system with APAR PH52141 applied

Front-end IMS: 3 checkpoints

Back-end IMS: 3 checkpoints

Front-end IMS: 2 checkpoints

Back-end IMS: 2 checkpoints
Back-end IMS system without APAR PH52141 applied

Front-end IMS: 3 checkpoints

Back-end IMS: 3 checkpoints

Front-end IMS: 2 checkpoints

Back-end IMS: 3 checkpoints
Important: While you can clean up inactive tpipes faster than before with the FASTTPCU function, the performance of your IMS systems could remain unchanged.