This section contains advice on how to manage secondary storage--that is, log stream data sets.
You are recommended to use System Managed Storage (SMS) to manage log stream data sets. You can specify the SMS characteristics of log data sets in a number of ways, depending on your installation:
If you omit the size parameter, the size is taken from the ALLOCxx member of PARMLIB (the default is 2 tracks, which leads to a high number of new data set allocations). Specify a size that is large enough to avoid a high frequency of new data set allocations--aim for a new data set to be allocated less often than once an hour.
For more information about managing log data sets, see the z/OS MVS Setting Up a Sysplex manual.
Redundant data should be deleted from log streams periodically, to conserve storage, and because the MVS system logger imposes a limit on the number of data sets per log stream.
CICS® manages the system log by deleting records, for completed units of work, during activity keypoint processing (log-tail deletion). With an appropriately sized log stream, the system log data remains in primary storage, so avoiding the overhead of data spilling to DASD.
Note that:
However, if historically you have used the system log for such things as audit trails, you may need to preserve system log data beyond the time it would normally be deleted by CICS. You can use the RETPD MVS parameter to preserve system log data. Define DFHLOG and DFHSHUNT to MVS with AUTODELETE(NO) and RETPD(dddd). The default values are AUTODELETE(NO) and RETPD(0).) Specifying AUTODELETE(NO) means that CICS, rather than MVS, retains control of the log-tail trimming process; dddd is the number of days for which data is to be retained. This causes the MVS logger to physically delete an entire log data set when all of the data in the data set:
You can view log data that has been marked for deletion by CICS but not yet physically deleted by MVS, using the DFHJUP utility program or the VIEW=ALL option of the MVS IXGBRWSE macro.
The number of data sets per log stream recognized by the MVS logger is several million. This means that, in general, you do not need to be concerned about the limit being reached.
You can cause redundant data to be deleted from log streams automatically, after a specified period. To arrange this for general log streams, define the logs to MVS with AUTODELETE(YES) and RETPD(dddd), where dddd is the number of days for which data is to be retained. This causes the MVS system logger to delete an entire log data set when all the data in it is older than the retention period (RETPD) specified for the log stream.