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Method for Concurrency Control for Syncpoint Log Record Access in a Coordinated Resource Recovery System

IP.com Disclosure Number: IPCOM000102102D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17

Publishing Venue

IBM

Related People

Ainsworth, MK: AUTHOR [+3]

Abstract

Disclosed is a method for controlling concurrent access to common recovery log records by processes cooperating or contending in the recovery from a syncpoint failure in a Coordinated Resource Recovery System.

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This is the abbreviated version, containing approximately 15% of the total text.

Method for Concurrency Control for Syncpoint Log Record Access in a Coordinated Resource Recovery System

       Disclosed is a method for controlling concurrent access
to common recovery log records by processes cooperating or contending
in the recovery from a syncpoint failure in a Coordinated Resource
Recovery System.

      Fig. 1 shows some elements of the Coordinated Resource Recovery
System including Syncpoint Managers (S1 and S2) in a hierarchical
relationship, utilizing a two-phase commit protocol for coordinating
the resources involved in a common transaction or cooperating
applications.  Each Syncpoint Manager is associated with a Recovery
Processor (S1-- R1 and S2-- R2) which is utilized to log syncpoint
information in anticipation of a failure during syncpoint and to
access log information for the recovery from syncpoint failures.

      The method assumes a set of latches for controlling
concurrency, where latches that can be held concurrently by the same
process are classified hierarchically to prevent deadlocks.  This
includes:
           a method for minimizing the time that a process
           hold exclusive access to a Syncpoint Log record by
           supporting cooperation between processes for
           access to the Syncpoint Log records based on the
           judicious use of status indicators, latching
           sequences, and latching options.  Syncpoint
           activities are given priority over recovery
           activities.

      This is important since syncpoint activities are associated
with running application that require fairly continuous but short
duration access to the Syncpoint Log, while relatively rare recovery
activities have the potential for holding the Syncpoint Log for
longer periods of time.
           a method of communication between processes that
           are completed and processes that are queued for the
           same Syncpoint Log record, such that control of
           and access to the Syncpoint Log record may be
           transferred (relinquished and regained) at
           appropriate times as required by the recovery
           process.

      Following are some of the contending functions involved in the
concurrency controls required by this method:
           LRW: Log Record Write creates a new log record.
           LRU: Log Record Update changes an existing log
           record.
           LRF: Log Record Find supports a set of search
           arguments for locating one or more Syncpoint Log
           records.  it is utilized by most of the functions
           on this list.
           LRE: Log Record Erase supports erasing a log
           record, generally at the completion of a syncpoint.
      ...