Contents of the log

IMS records activity on the OLDS. CQS records activity on a z/OS® log stream. Each different activity is recorded as a separate log record.

Generally, you do not need to know the content of log records. IMS and CQS identify the correct records and use them automatically when they perform recovery.

The following items, however, should be kept in mind with respect to the logs:

• Log reduction

  As part of log reduction, IMS compresses log data. IMS compresses repeated single characters, such as blanks and zeros, in the segment data portions of log records. This compression applies to updates resulting from DL/I insert (ISRT), delete (DLET), and replace (REPL) calls.

  The counterpart to compression is expansion. During backout and database recovery, IMS expands the data in the database buffer. For change accumulation data sets, IMS expands the data in the change accumulation record.

• Logging and the Data Capture exit routine

  IMS does not write log records for the Data Capture exit routine to show that it has been called, nor does IMS write the exit routine name in any log records. IMS does not differentiate between the application program and the exit routine. If you use the Data Capture exit routine extensively, your IMS system accounting and performance monitoring information is likely to show more system use for the application programs than they actually use.

Related reading: If you need to examine log records to solve a complex recovery problem, see IMS Version 15.5 Diagnosis.