Red Alert : Potential data corruption for IMS or DB2 for z/OS

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Potential data corruption for IMS or DB2 for z/OS following rebuild of lock structure in data sharing mode.

Description:

During rebuild of a lock structure in a DB2 V8 or DB2 V9 data sharing environment, two problems may occur when locks are being rebuilt asynchronously into the new structure:

1. The IRLM may incorrectly conclude that the rebuild is complete before all locks have been rebuilt into the new lock structure. This can cause new lock requests to be granted prematurely, resulting in incompatible locks being held across the data sharing group.
2. The IRLM may ABEND before all locks have been rebuilt. In this case, locks that were not rebuilt in time will be lost and will not be reacquired on restart.

In both cases potential data loss or data corruption may result either during or following the rebuild event.

Since the problem is in IRLM, all versions of IMS may also be affected.

No recent DB2, IMS or IRLM maintenance has affected the possibility of encountering this issue.

The resolution to the above issues will be provided by IRLM APAR PM23662.

Recommended Action:

Install ++APAR for PM23662 which is now available. If possible, avoid rebuild of IRLM lock structures until the solution for PM23662 is applied to all members of the data sharing group. If rebuild of the lock structure is unavoidable, then consider performing the rebuild with a single active member. This would require quiescing all the other members. If data corruption is detected following a lock structure rebuild, quiesce and restart all members of the group to prevent further problems.

Alternatively,for customers planning to do a Rebuild before the ++APAR can be installed on all members of the data sharing group (e.g. CF upgrade or processor upgrade with ICF in the near term), please contact IBM Support for IRLM to determine if a procedural bypass can be provided in your configuration.

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