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 CICS log manager 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.
Auxiliary storage—when the primary storage for a log stream
becomes full, the older records automatically spill into auxiliary
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 1 and Figure 2 show the types of storage used by the CICS system logger. Figure 1. The types of storage used by the MVS system logger. This diagram shows a log
stream that uses a coupling facility. Primary storage consists of
space in a structure within the CF, and either staging data sets or
a data space in the same MVS image as the system logger.
Figure 2. The types of storage used by the MVS system logger. This diagram shows a log stream that
uses DASD-only logging. Primary storage consists of a data space in
the same MVS image as the system logger, and a single
staging data set.
