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Locking Scheme for an Object-Oriented Database

IP.com Disclosure Number: IPCOM000105990D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Calo, SB: AUTHOR [+3]

Abstract

Disclosed is an algorithm for locking classes and objects in an object-oriented database which supports concurrent access to the database and on-line changes to the database schema.

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

Locking Scheme for an Object-Oriented Database

      Disclosed is an algorithm for locking classes and objects in an
object-oriented database which supports concurrent access to the
database and on-line changes to the database schema.

      The database consists of objects, classes, and super classes.
Each object belongs to a class called its parent.  An object may
belong to only one class.  Each class has one parent (a super class).

A super class may have only one parent (another super class); and
there is only one super class with no parent, the universal super
class.

      The database has two kinds of locks, exclusive locks and
shared/ exclusive locks.  An exclusive lock may be held in exclusive
mode only.  Each database object has its own exclusive only lock.
Each database class has a shared/exclusive lock.  There is one super
class lock.

      In fact, the database has five major types of locks.  These
locks are the Class Hash Table Lock, the Object Hash Table Lock, and
Object Lock, the Super Class Lock, and the Class Lock.

      These locks are arranged into a partially ordered set.  Figure
1 shows the partial ordering for the five major types of locks in the
data base.  At the lowest level of the ordering is the Class Hash
Table Lock.  The Class Lock is at the highest level of the ordering.
Note that not all locks are related in the ordering.  The Super Class
Lock and the Object Lock are not related.

      Partially ordering the locks helps avoid deadlock.  The
following deadlock free scheme is used.  Locks must be obtained in
order.  To hold a high lock, al...