How the logs are written
WebSphere MQ writes each log record to a DASD data set called the active log. When the active log is full, WebSphere MQ copies its contents to
a DASD or tape data set called the archive log. This
process is called off-loading.
Figure 10 illustrates the process of logging. Log records
typically go through the following cycle:
- WebSphere MQ notes changes to data and significant events in recovery log records.
- WebSphere MQ processes recovery log records and breaks them into segments, if
necessary.
- Log records are placed sequentially in output log buffers, which are formatted as VSAM CIs. Each log record is identified by
a relative byte address in the range zero through 248-1.
- The CIs are written to a set of predefined DASD active log data sets,
which are used sequentially and recycled.
- If archiving is active, as each active log data set becomes full, its
contents are automatically off-loaded to a new archive log data set.