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Browse Prior Art Database

Phantom Lock With Intended Exclusive for Browsing

IP.com Disclosure Number: IPCOM000102419D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Tate, BA: AUTHOR [+2]

Abstract

Databases frequently allow a user to browse a record before deciding to update it. Current locking protocols do not accommodate this function well. Disclosed is a locking scheme that solves this problem. A new type of lock, called a Phantom Lock, is provided for this purpose. It is called a Phantom Lock because it does not exist for the purposes of two phased locking. The primary use of the lock will be to register the users of a record with the underlying database management system so that the record may be updated dynamically by the system when another process modifies it. If the process intends to update this record, the system will issue PX (phantom to exclusive) lock to the process intending the update.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 77% of the total text.

Phantom Lock With Intended Exclusive for Browsing

       Databases frequently allow a user to browse a record
before deciding to update it.  Current locking protocols do not
accommodate this function well.  Disclosed is a locking scheme that
solves this problem.  A new type of lock, called a Phantom Lock, is
provided for this purpose.  It is called a Phantom Lock because it
does not exist for the purposes of two phased locking.  The primary
use of the lock will be to register the users of a record with the
underlying database management system so that the record may be
updated dynamically by the system when another process modifies it.
If the process intends to update this record, the system will issue
PX (phantom to exclusive) lock to the process intending the update.
At this point, no new process may obtain an S lock on the record
until the PX lock is upgraded to an X lock, and the X lock released,
ensuring that S locks will clear.  Note that with standard 2PL, a
process is not guaranteed an X lock if the record in question is
frequently accessed in a highly concurrent system because new S locks
are not locked out.

      Phantom locks should be used for display only for consistency.
The primary uses of the P-lock are to look at a value before possibly
updating it and to register the value with the system so that the
process will be notified if its corresponding data value changes.
When a database record changes, all processes that hold a P-lock on
the reco...