IBM SC34-7012-01 manual Merging data on shared general log streams, Defining the log of logs

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

vYou 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.

vYou 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:

vYou 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.

vAll data sets used by one transaction should use the same log stream (to reduce the number of log streams written to at syncpoint).

vShare 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.

vThe 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.

vDon'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.

vDon't put all frequently updated data sets on a single log stream because you could exceed the throughput capacity of the log stream.

vIf 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.

vDelete 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.

vRelate log stream names to the data sets. For example, PAYROLL.data_sets could be mapped to a forward recovery log named PAYROLL.FWDRECOV.PAYLOG.

vAvoid 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.

118CICS TS for z/OS 4.1: Recovery and Restart Guide