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An explanation of BACKODUR, and why you shouldn't set it to zero

Can you explain why it's not a good idea to set BACKODUR to 0?

BACKODUR is the system parameter that controls BACKOUT DURATION (DSNZPxxx: DSN6SYSP BACKODUR). It is specified...

as a number between 0 and 255, with a default value of 5. The value you specify for BACKOUT DURATION is your indication of how many log records are to be read during restart's backward log scan.

The BACKOUT DURATION field is a multiplier of the value you specify for the number of log records per checkpoint value (the CHECKPOINT FREQ field on DSNTIPN). Use this combination of values to ensure that short-duration URs are handled during restart rather than being postponed.

BACKODUR indicates how much of the log to process for backout when LIMIT BACKOUT = YES or AUTO. During restart, backward log processing continues until both (1) all inflight and inabort URs with update activity against the catalog or directory are backed out and (2) the number of log records processed is equal to the number specified in BACKODUR multiplied by the number of log records per checkpoint. If the checkpoint frequency type is minutes (instead of number of log records), then a default value of 50,000 log records will be used.

So, with that background, specifying a BACKODUR value of 0 will negate the second condition for stopping backward log processing during restart (that is, 0 log records).

This was last published in March 2003

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