IBM SC34-7012-01 manual Defining forward recovery log streams, Long-running transactions

About this task

The dddd value specifies the minimum number of days for which data is to be retained on the log.

You are strongly recommended not to use the system log for records that need to be kept. Any log and journal data that needs to be preserved should be written to a general log stream. See the CICS System Definition Guide for advice on how to create general log stream data sets.

Long-running transactions

Do not design long-running transactions in such a way that they write frequently to the system log stream, in a single unit of work, across multiple activity keypoints.

If a long-running transaction does not take regular syncpoints while regularly initiating writes to the system log, CICS is prevented from purging units of work that completed after the long-running task started.

In Figure 11, the long-running transaction is updating recoverable resources, causing writes to the system log. All the updates are in the same unit of work because it does not take explicit syncpoints. The oldest deletion point is earlier than activity keypoint number 5, preventing CICS from deleting any completed units of work that lie between activity keypoints 5 and 8. In this example, the long-running transaction will eventually cause the system log stream to spill onto secondary storage.

System-log-stream

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AKP

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x	x	x	x	x	x	x	x	x	x
Long running transaction :
		Each X represents			an update to a recoverable
		resource, causing			a write to the system log.

Figure 11. The effect of a ‘bad’ long-running transaction

Defining forward recovery log streams

You must define forward recovery logs for VSAM data sets that are defined as recoverable files. Neither CICS nor VSAM provides any support for forward recovery logging for a nonrecoverable data set.

About this task

Procedure

1.Define recovery attributes for data sets, 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” on page 126 for details.

116CICS TS for z/OS 4.1: Recovery and Restart Guide