Archiving

Because the active log has a fixed size, WebSphere MQ copies the contents of each log data set periodically to an archive log, which is normally a data set on a direct access storage device (DASD) or a magnetic tape. If there is a subsystem or transaction failure, WebSphere MQ uses the active log and, if necessary, the archive log for recovery.

The archive log can contain up to 1000 sequential data sets. We can catalog each data set using the z/OS integrated catalog facility (ICF).

Archiving is an essential component of WebSphere MQ recovery. If a unit of recovery is a long-running one, log records within that unit of recovery might be found in the archive log. In this case, recovery requires data from the archive log. However, if archiving is switched off, the active log with new log records wraps, overwriting earlier log records. This means that WebSphere MQ might not be able to back out the unit of recovery and messages might be lost. The queue manager then terminates abnormally.

Therefore, in a production environment, never switch archiving off. If you do, you run the risk of losing data after a system or transaction failure. Only if you are running in a test environment can you consider switching archiving off. If we need to do this, use the CSQ6LOGP macro, which is described in the WebSphere MQ for z/OS System Setup Guide.

To help prevent problems with unplanned long-running units of work, WebSphere MQ issues a message (CSQJ160I or CSQJ161I) if a long-running unit of work is detected during active log offload.