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Browse Prior Art Database

Effective Locking Scheme for Real-Time Applications

IP.com Disclosure Number: IPCOM000105112D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Wu, K: AUTHOR [+2]

Abstract

Disclosed is the development of a locking scheme for real-time applications to reduce the percentage of transactions missing the deadline.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Effective Locking Scheme for Real-Time Applications

      Disclosed is the development of a locking scheme for real-time
applications to reduce the percentage of transactions missing the
deadline.

      Transactions on real-time databases have a timing constraint
associated with them.  In general, this constraint is expressed in
the form of a deadline which indicates that transactions must be
completed before a certain time in the future [1].  In real-time
systems, CPU scheduling policy with dynamic priority assignment is
often used to increase the priority of tasks with deadline
approaching so they can get scheduled to meet the deadline
requirement.  In the transaction processing environment, the
concurrency control protocols can reduce the effectiveness of this
kind of dynamic scheduling approach [2,3].  Under a locking based
protocol, low priority jobs can block the high-priority transactions
by holding their required locks [4].

      The proposed scheme uses a deferred blocking approach.  delta
is defined to be the critical interval of a transaction execution in
order to meet its deadline.  Note that delta can be chosen to be
slightly larger than the transaction execution time.  When a
transaction first gets executed, it is in a deferred blocking mode
assuming the time to its deadline is larger than the critical
interval.  It only needs to obtain a weak lock on the granule it
accesses.  If there is already a strong lock held on exclusive mode,
the transaction will wait.

      The proposed scheme tracks the progress of each transaction.
When the transaction is within delta interval to its deadline, the
transaction enters its critical stage.  The proposed scheme would try
to convert all granules it currently held with weak locks into strong
locks.  If only weak locks or compatible strong locks are held on a
requested granule by other transactions, the conversion on that
granule will be successful.  If successful on all granules requested,
the transaction enters into blocking mode and would request a strong
lock for each subsequent granule access.  If unsuccessful, the
transactions will be aborted and restarted with blocking mode.  Note
however, if at conversion time transaction is currently waiting on a
strong lock and other locks can be con...