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MAXM Reorg/Online for IMS
Why would I want to use the combination of BMCPause & DBRSCOPE(P) in an online reorg?
The online reorg function of MAXM requires short periods of exclusive control over a database object during the reorg process. This was originally accomplished by issuing a /DBR of the database to release it from IMS. As HAL/DB became more mainstream, we introduced (and Patented) the BMC Pause technology as an alternative to taking a database offline during the online reorg process. BMCPause leaves the database online, but stops processing against the database, to provide a "Quiet Point" on the database. This was sufficient for MAXM to eliminate the first two outage periods ( /DBR - /STA sequences) of the online reorg process. The third and final outage period still requires a /DBR to remove the database from IMS so the datasets that make up the database, could be physically swapped with a reorganized version of the same dataset.
This can cause problems for HAL/DB as often there are a large number of partitions and an even larger number of datasets to manage. The DBRSCOPE technique was introduced to exploit the HAL/DB architecture and issue the required /DBR commands at the partition level rather than at the Master Database level.
Hogan software contains a piece of code called Umbrella that is an application layer to translate generic application requests into database requests. The Umbrella code checks the availability of a database before letting a transaction process. If the database is offline, the transaction will not be allowed to process and a return code (failed transaction) is returned to the user. Since the transactions are never sent to IMS, there is no logging of the transaction, and the transactions are essentially dropped.
The condition is addressed by the combination of BMCPAUSE and DBRSCOPE as follows:
- BMCPAUSE is issued at the Master DB level to quiesce all activity against the database. However, the database appears online to IMS.
- DBRSCOPE(P) Causes MAXM to issue the /DBR commands at the partition level, thus leaving the Master Database online
- Umbrella will continue to function because it sees the database online, however, any transaction that comes in will be held until the Pause is released.