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DFHJCP

DFHJCP is the CICS journal control program that provides facilities for creating, controlling, and retrieving a special series of data sets called journals during real-time CICS execution. Journals record, in chronological order, any data the user might need later to reconstruct data or events. For example, journals can act as audit trails, record database updates, additions, and deletions for backup, or track transaction activity in the system.

For each transaction, journal control maintains a dynamic log of all changes to recoverable resources. This log allows dynamic backout to recover any such changes if a transaction failure occurs.

Hints

The JCT BUFSIZE=nnnnn is the parameter that controls the blocking of journal write operations. A large value, therefore, can minimize physical write operations. This potential benefit does not happen if all the journal writes are requested as synchronous operations. For tape files, consider BUFSIZE=32767. On disk drives, specify a size that will allow two blocks per track.

The JCT BUFSUV=nnnn is the parameter that starts asynchronous write operations to the journal when the specified buffer shift-up value is reached. If this value is not provided, when the journal buffer is full, synchronous write operations occur. Consider a value that will leave room for two to five more records in the buffer. Determine the average journal record size by examining the journal statistics.

The JCT JREQ=ALL/request is the parameter that controls whether journal write operations are synchronous or asynchronous with the file activity. Consider JREQ=(ASY, WN, WU) after you evaluate your recovery requirements. Requesting asynchronous journal writes creates a small integrity exposure. The output operation to the journal data set starts when the record is moved to the journal buffer. The journal might not reflect the change to the data set if a crash occurs during this time. Asynchronous writes usually lower transaction response time.

Reference Sources

CICS Tuning and Performance, Xephon Report, I. Gelb, August 1991.

CICS Transaction Server for z/OS Diagnosis Reference