Db2 for z/OS

Update on the Rebind phase-in capability added in FL 505

By Tim Hogan posted Fri September 04, 2020 11:52 AM

By Tammie Dang and Tim Hogan

Db2 12 function level 505 introduced a new REBIND phase-in capability for application packages, which enables DBAs to issue REBIND PACKAGE commands successfully when target packages are being concurrently executed. This feature was supported for the PLANMGNT(EXTENDED) bind option.

Prior to FL 505, REBIND obtains the package lock in an incompatible state with transactions executing the package. The REBIND can wait up to 3x the IRLMRWT interval to acquire the package lock. Transactions that start after the REBIND could experience similar wait times since their package lock request are queued up behind the REBIND request.

Starting with FL 505, one of the benefits of REBIND phase-in is a reduction in the amount of transaction wait time when a package lock is requested during REBIND. In fact, with the REBIND phase-in capability introduced in FL 505, the maximum wait time for a REBIND on the package lock which could affect subsequent transaction wait times was shortened from 3x to 1x of the IRLMRWT.

However, even with FL 505, transactions that start immediately after a REBIND command is initiated must still wait for the REBIND to relinquish its package lock or lock request.  A transaction's elapsed time can increase by the amount of the REBIND's wait time for the package lock and the processing time for the REBIND.  With FL 505, the REBIND wait time is reduced to 1x IRLMRWT seconds, and REBIND processing can run in parallel with the transaction if phase-in processing is in effect.

In summary, transaction wait times and rebind concurrency have both improved with FL 505 since rebinds are less likely to time out and transactions waiting behind a REBIND will wait less time than previously. However, there remains a timing window where transactions can wait for REBIND to finish, as in function levels prior to FL 505.

1Q 2021 APARs related to the REBIND phase-in capability:

APAR PH28693 (UI73874) introduces a change that will improve the REBIND concurrency of Db2 on FL505. A REBIND will now always obtain a U lock, allowing subsequent transactions that are executing a package to run in parallel. This change applies when the package is rebound with the PLANMGMT(EXTENDED) option.

APAR PH33295 (UI74599), which is available now, provides new options to free unused phased-out copies which could be created when a package is rebound. The freeing of phased-out package copies is recommended in order to reduce space in the Db2 directory and catalog.
Tammie Dang is a Senior Software Engineer in Db2 for z/OS development and Tim Hogan is an Information Developer for Db2 for z/OS.
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