Tuning the performance of timeout delete

A careful choice of DSHIPINT and DSHIPIDL settings results in a minimal number of mass deletions of shipped definitions, and a scheduling of those that do take place for times when your system is lightly loaded. Conversely, a poor choice of settings could result in unnecessary mass delete operations. Here are some suggestions for coding DSHIPINT and DSHIPIDL:

DSHIPIDL

In setting this value, you must consider the length of the work periods during which remote users access resources on this system. Do they access the system intermittently, all day? Or is their work concentrated into intensive, shorter periods?

By setting too low a value, you could cause definitions to be deleted and reshipped unnecessarily. It is also possible that you could cause automatic transaction initiation (ATI) requests to fail with the "terminal not known" condition. This condition occurs when an ATI request names a terminal that is not defined to this system. Usually, the terminal is not defined because it is owned by a remote system, you are using shippable terminals, and no prior transaction routing has taken place from it. By allowing temporarily inactive shipped definitions too short a life, you could increase the number of calls to the XALTENF and XICTENF global user exits that deal with the "terminal not known" condition.

DSHIPINT

You can use this value to control the time of day at which your mass delete operations take place. For example, if you usually warm-start CICS® at 7 a.m., you could set DSHIPINT to 150000, so that the timeout delete mechanism is invoked at 10 p.m., when few users are accessing the system.

Attention: If CICS is recycled, perhaps because of a failure, the timeout delete interval is reset. Continuing the previous example, if CICS is recycled at 8:00 p.m., the timeout delete mechanism will be invoked at 11:00 a.m. the following day (15 hours from the time of CICS initialization). In these circumstances, you could use the SET DELETSHIPPED and PERFORM DELETSHIPPED commands to accurately control when a timeout delete takes place.

CICS provides statistics to help you tune the DFHIPIDL and DFHIPINT parameters. The statistics are available online, and are mapped by the DFHA04DS DSECT. For details of the statistics provided, see the CICS Performance Guide.

Related concepts
Overview of how shipped terminals are deleted
Related tasks
Implementing timeout delete
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