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Merging data on shared general log streams
Unlike system log streams, which are unique to one CICS region, general log
streams can be shared between many CICS regions. This means that you can
merge forward recovery data from a number of CICS regions onto the same
forward recovery log stream.
About this task
v You can use the same forward recovery log stream for more than one data set.
You do not have to define a log stream for each forward-recoverable data set.
v You can share a forward recovery log stream between multiple CICS regions. If
the regions are accessing a data set in RLS mode, the use of the same forward
recovery log stream is forced.
Your decision on how to define and allocate forward recovery log streams is a
trade-off between transaction performance, fast recovery, and having a large
number of log streams to manage.
Some things to consider are:
v You can share a coupling facility log stream across multiple CICS regions that
run in the same or in different MVS images. You can share a DASD-only log
stream only across CICS regions that run in the same MVS image.
v All data sets used by one transaction should use the same log stream (to reduce
the number of log streams written to at syncpoint).
v Share a forward recovery log stream between data sets that:
– Have similar security requirements
– Have similar backup frequency
– Are likely to need restoring in their entirety at the same time.
v The last qualifier of the stream name is used as the CICS resource name for
dispatcher waits. Therefore, a self-explanatory qualifier can be helpful when you
are interpreting monitoring information and CICS trace entries.
v Don't mix frequently updated data sets with infrequently updated data sets on
the same forward recovery log, because this causes a disproportionate amount of
unwanted log data to be read during recovery of infrequently updated data sets.
v Don't put all frequently updated data sets on a single log stream because you
could exceed the throughput capacity of the log stream.
v If you define too many data sets to a single log stream, you could experience
frequent structure-full events when the log stream can't keep up with data flow.
v Delete redundant data from log streams periodically, to preserve secondary
storage and so that the system logger does not exceed its limit of data sets per
log stream. (The limit is several million and in normal circumstances it is not
likely to be exceeded.) See the CICS Transaction Server for z/OS Installation Guide
for information about managing log stream data sets.
v Relate log stream names to the data sets. For example, PAYROLL.data_sets could
be mapped to a forward recovery log named PAYROLL.FWDRECOV.PAYLOG.
v Avoid having too many forward recovery log streams, because of coupling
facility log structure limits.
Defining the log of logs
Define a log of logs log stream, and define a JOURNALMODEL resource definition
that references that log stream.
118 CICS TS for z/OS 4.1: Recovery and Restart Guide