Online change performance considerations

Depending on what you are using the online change function for, different performance considerations apply.

Deleting databases from the MODBLKS data set

Deleting databases from MODBLKS using Online Change incurs the performance overhead of reading the intent lists from ACBLIB for all application programs in MODBLKS whose intent lists are not loaded.

This is necessary to determine which transactions need to stop queuing, to prevent work that might cause commit to fail. This performance overhead is proportional to the number of application programs defined in MODBLKS for which the intent list is not loaded.

Recommendation: If you need to delete databases from MODBLKS, consider performing an IMS cold start instead of using local or global online change.

Modifying ACB members

By default, when a DBD is specified on the NAME keyword of the INITIATE OLC PHASE(PREPARE) TYPE(ACBMBR) command, the ACB member online change (OLC) function automatically copies all associated PSBs and externally referenced DBDs from the staging ACB library to active ACB library. Depending on the number of PSBs and DBDs, the amount of time required for the copying process can be significant.

In many cases, you can significantly reduce the amount of time the ACB member online change function takes by specifying OPTION(NAMEONLY) on the INITIATE OLC PHASE(PREPARE) TYPE(ACBMBR) command. The NAMEONLY option limits the processing of the ACB member online change function to only the DBDs and PSBs that are specified in NAME() keyword of the command.