Using transaction classes DFHTCLSX and DFHTCLQ2 to control storage use
Use DFHTCLSX and DFHTCLQ2 in RDO group DFHISCT to control the amount of storage used by CICS® to run the CLS1, CLS2, and CLQ2 transactions.
Effects
These tasks execute the activities needed to acquire an APPC conversation (CLS1/2), and to resynchronize units of work for MRO and APPC connections (CLQ2). Typically there are not many tasks, and they need no control. However, if your CICS system has many connection definitions, these connections might be acquired simultaneously as a result of initializing the system at startup, or as a result of a SET VTAM OPEN or SET IRC OPEN command.
How implemented
The system definitions are optional. Install resource group DFHISCT to activate them. As supplied, the MAXACTIVE parameter in the DFHTCLSX and DFHTCLQ2 is 25. This value gives sufficient control to prevent the system reaching a short-on-storage situation. Tasks CLS1 and CLS2 each require 12 KB of dynamic storage, and CLQ2 tasks require up to 17 KB. Do not set the purge threshold to a non-zero number and do not set the MAXACTIVE parameter to 0. Both values might prevent CICS from running tasks necessary to intersystems functions.
Do not set the MAXACTIVE value too low, because network delays or errors might cause one of the tasks in the TCLASS to wait and block the use of the TCLASS by succeeding transactions. Setting a low value can also extend shutdown time in a system with many connections.