Defining forward recovery log streams

VSAM data sets defined as recoverable files must have associated forward recovery logs. In the event of physical failure or corruption, restore the most recent backup, and use a forward recovery utility such as CICSVR to re-apply updates.

To recover from a DASD failure, first restore the most recent backup to a new data set. Then use a forward recovery utility, such as CICS® VSAM Recovery (CICSVR), to apply all the updates that were written to a forward recovery log stream after the backup date.

Note:
Define a data set as recoverable if you want forward recovery logging. Neither CICS nor VSAM provides any support for forward recovery logging for a nonrecoverable data set.

Defining recoverable data sets

You specify recovery attributes, including forward recovery, in either the integrated catalog facility (ICF) catalog (if you are using DFSMS 1.3 or later), or in the CICS file resource definition. See Defining files as recoverable resources for details.

Model log streams for CICS general logs

If CICS fails to connect to a general log stream because it has not been defined, CICS attempts to have it created dynamically. To create a log stream dynamically, CICS must specify to the MVS™ system logger all the log stream attributes needed for the new log stream. To determine these otherwise unknown attributes, CICS requests the MVS system logger to create the log stream using attributes of an existing model log stream definition. If you decide to allow CICS to create log streams dynamically, you are responsible for creating the required model log stream definitions to ensure that dynamic creation succeeds.

It is generally worthwhile setting up model log streams only if:

Otherwise, it is probably less work to define the log streams explicitly using IXCMIAPU.

The default model log stream names that CICS uses for dynamic creation of a general log stream are of the form LSN_qualifier1.LSN_qualifier2.MODEL where the first and second qualifiers are the CICS region userid and the CICS APPLID, respectively.

Example: If a CICS region, running under userid CICSHA## with APPLID=CICSHAA1, issues a request to create a general log stream that is not defined by a JOURNALMODEL resource definition, CICS specifies CICSHA##.CICSHAA1.MODEL as the model log stream name.

See Model log streams for CICS system logs for information about using an XLGSTRM global user exit program to modify requests to create a log stream.

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:

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:

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