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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.
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.
System-log-stream
AKP AKP AKP AKP AKP
5
6
7
89
Long running transaction :
Each X represents an update to a recoverable
resource, causing a write to the system log.
x x x x x x x x x x
x x x x x x x x x x
Figure 11. The effect of a ‘bad’ long-running transaction
116 CICS TS for z/OS 4.1: Recovery and Restart Guide