Planning to increase the maximum addressable log range

You can increase the maximum addressable log range by configuring your queue manager to use a larger log relative byte address (RBA).

The log RBA size was increased from IBM® MQ for z/OS® 8.0. For an overview of this change, see Larger log Relative Byte Address.

Queue managers created at IBM MQ 9.3.0 or later, have 8 byte log RBA enabled by default and, therefore, do not require conversion.

You can convert your queue managers to use 8 byte log RBA values at any time. A queue sharing group can contain some queue managers with 8 byte log RBA enabled, and some queue managers with 6 byte log RBA enabled.

Undoing the change

The change cannot be backed out.

How long does it take?

The change requires a queue manager restart. Stop the queue manager, run the CSQJUCNV utility against the bootstrap data set (BSDS), or data sets, to create new data sets, rename these bootstrap data sets, and restart the queue manager. The CSQJUCNV utility usually takes a few seconds to run.

What impact does this have?

With 8 byte log RBA in use, every write of data to the log data sets has additional bytes. Therefore, for a workload consisting of persistent messages there is a small increase in the amount of data written to the logs.
Data written to a page set, or coupling facility (CF) structure, is not affected.