CICS transient data (TD) facility: Performance and tuning

Transient data (TD) is used in many circumstances within CICS®, and various options can affect the performance of this facility.

The circumstances in which transient data is used include:
  • Servicing requests made by user tasks, for example, a request to build a queue of data for later processing.
  • Servicing requests from CICS, primarily to write messages to system queues for printing. Transient data should, therefore, be set up at your installation to capture these CICS messages.
  • Managing the DASD space holding the intrapartition data.
  • Initiating tasks based on queue trigger level specification and on records written to an intrapartition destination.
  • Requesting logging for recovery as specified in your CICS transient data definitions.
  • Passing extrapartition requests to the operating system access method for processing.

Limitations

Application requirements might dictate a lower trigger level, or physical or logical recovery, but these facilities increase processor requirements. Real and virtual storage requirements might be increased, particularly if several buffers are specified.

Implementation

Transient data performance is affected by the TRIGGERLEVEL and RECOVSTATUS operands in the transient data resource definitions that have been installed.

Recommendations

The following suggestions might help to reduce waits during QSAM processing:
  • Avoid specifying a physical printer.
  • Use single extent data sets whenever possible to eliminate waits resulting from the end of extent processing.
  • Avoid placing data sets on volumes that are subject to frequent or long duration RESERVE activity.
  • Avoid placing many heavily-used data sets on the same volume.
  • Choose BUFNO and BLKSIZE such that the rate at which CICS writes or reads data is less than the rate at which data can be transferred to or from the volume; for example, avoid BUFNO=1 for unblocked records whenever possible.
  • Choose an efficient BLKSIZE for the device employed such that at least three blocks can be accommodated on each track.

Monitoring

The CICS statistics show transient data performance. CICS transient data statistics can be used to determine the number of records written or read. Application knowledge is required to determine the way in which the lengths of variable length records are distributed. CICS transient data statistics also show the peak size of each intrapartition transient data queue during the statistics interval. RMF or the VSAM catalog shows data set performance.