A log stream is a sequence of data blocks, with each log stream identified
by its own log stream identifier--the log stream name (LSN). The CICS® system log, forward recovery logs, and user journals map onto specific MVS™ log
streams. CICS forward recovery logs and user journals are referred to as general
logs, to distinguish them from system logs.
Each log stream is a sequence of blocks of data, which the MVS system logger internally
partitions over three different types of storage:
- Primary storage, which holds the most recent records written to the log
stream. Primary storage can consist of either:
- A structure within a coupling facility. (The use of a coupling facility
allows CICS regions in different MVS images to share the same general log streams.)
Log data written to the coupling facility is also copied to either a data
space or a staging data set.
- A data space in the same MVS image as the system logger. Log data written
to the data space is also copied to a staging data set.
- Secondary storage--when the primary storage for a log stream becomes
full, the older records automatically spill into secondary storage, which
consists of data sets managed by the storage management subsystem (SMS). Each
log stream, identified by its log stream name (LSN), is written to its own
log data sets.
- Tertiary storage--a form of archive storage, used as specified in
your hierarchical storage manager (HSM) policy. Optionally, older records
can be migrated to tertiary storage, which can be either DASD data sets or
tape volumes.
Figure 58 and Figure 59 show the types of storage
used by the MVS system logger.
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