Question & Answer
Question
One is planning on adding additional active logs to their DB2 for z/OS subsystem. This will be done by using the -SET LOG command to dynamically add the logs. If one currently has 8 dual active log datasets and plans to double this number to 16 and DB2 currently allocates the active logs in sequence from 1 to 8, what happens when the added logs 9 thru 16, will DB2 maintain the sequence of allocation (ie. 1 thru 16 in sequence). Must one issue -ARCHIVE LOG commands to cause the active log to be positioned to DS08 before issuing the -SET LOG commands to add logs 9 thru 16 so as to maintain the sequence of active log allocations by DB2 or can one count on DB2 to continue to allocate DS05 through DS08 in sequence and then begin allocating DS09 through DS16 after DS08?
Answer
First off, the newly added and initialized logs will be used in the reverse order from which they were added when using the -SET LOG command. This is opposite to the order they will be used when adding them via the DSNJU003 utility, where they will be used in the same order as they were added in. For more info on this see the section titled "Order in which newly defined active log data sets are used" under the SET LOG command URL below.
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With regards to your already existing DB2 active log data sets, DB2 will insert a newly added entry into the active log data set record following the last or latest active log data set with a sequence number marked as NOTREUSABLE (which indicates that the RBA range on that data set has not yet been offloaded).
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Let me include an example:-
DS01 - reusable
DS02 - non-reusable
DS03 - reusable
DS04 - reusable
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add DS05 & DS06
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Now the sequence will be...
1->2->5->6->3->4 after the NEWLOG operation.
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Modified date:
03 September 2021
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