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Optimistic Concurrency Control With Waiting

IP.com Disclosure Number: IPCOM000099964D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Dias, DM: AUTHOR [+2]

Abstract

Disclosed in a Concurrency Control (CC) method for a transaction processing system that improves performance by reducing transaction aborts due to locks held by transactions that are in commit processing. In Optimistic Concurrency Control (OCC), transactions check for conflict at commit time and are aborted if a conflicting access is detected. However, transactions typically hold locks during commit processing, and transactions are aborted if a conflicting lock is held by transactions in commit. In a multi-system environment the commit processing time when locks are held becomes longer. This occurs in a closely coupled system with shared DASD (1) because updates need to be reflected to the shared DASD before the (commit) locks can be released.

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Optimistic Concurrency Control With Waiting

       Disclosed in a Concurrency Control (CC) method for a
transaction processing system that improves performance by reducing
transaction aborts due to locks held by transactions that are in
commit processing. In Optimistic Concurrency Control (OCC),
transactions check for conflict at commit time and are aborted if a
conflicting access is detected. However, transactions typically hold
locks during commit processing, and transactions are aborted if a
conflicting lock is held by transactions in commit. In a multi-system
environment the commit processing time when locks are held becomes
longer. This occurs in a closely coupled system with shared DASD (1)
because updates need to be reflected to the shared DASD before the
(commit) locks can be released. In a geographically distributed
database system, a two-phase commit is typically used leading to a
relatively long commit time. For these cases, the probability that a
transaction is aborted under the OCC protocol increases. In (2), it
is shown how the commit time when locks are held manifests itself as
an increased abort probability.  This increased abort probability can
be reduced using the disclosed method, referred to as OCC with wait.

      In the disclosed OCC with wait protocol, a transaction informs
the CC manager when each granule is to be accessed. If a strong lock
is held on the granule in incompatible mode, the request is placed in
a wait queue until the lock on...