Method and system for selectable consistency level maintenance in a resilent database system

• US 5,796,999 A
• Filed: 04/15/1994
• Issued: 08/18/1998
• Est. Priority Date: 04/15/1994
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Satran, Julian, Goft, German, Dolev, Danny, Ranweiler, James Gregory, Azagury, Alain Charles, Marberg, John Michael
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Alam, Hosain T.
• Application Number:
  US08/228,319
• Time in Patent Office: 1,586 Days
• Field of Search: 395/425, 395/575, 395/600, 395/650, 395/445, 395/200.03
• US Class Current: 1/1
• CPC Class Codes: G06F 11/2094 Redundant storage or storage space G06F11/2056 takes precedence
• CPC Class Codes: G06F 11/2097 maintaining the standby controller/processing unit updated initialisation or re-synchronisation thereof G06F11/1658 and subgroups
• CPC Class Codes: G06F 16/2365 Ensuring data consistency and integrity
• CPC Class Codes: G06F 2201/80 Database-specific techniques
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

In a resilient database system which includes a journaled database which is implemented at one or more locations within a distributed data processing system, multiple diverse consistency levels are specified which each detail a level of consistency to be maintained between a primary database and a replica database. A user is then permitted to select a particular level of consistency for each replica database. Thereafter, each update to a record within the primary database is utilized to initiate an update to the corresponding record within each replica database in a manner which is consistent with the selected level of consistency for that replica database. In this manner, a replica database which is fully consistent with the primary database may be provided for seamless switchover in the event of a primary database failure, while a second replica database may be provided to respond to queries by applications which do not require fully consistent data, greatly enhancing the efficiency of access to that database.

Claims

1. A method for enhanced efficiency in database access within a distributed data processing system, said method comprising the steps of:

designating a selected database within said distributed data processing system as a primary database, said selected database having a plurality of records stored therein;

replicating said primary database at at least two physical locations within said distributed data processing system;

specifying a plurality of diverse consistency levels which may be maintained between said primary database and each of said replicated databases;

permitting a user to specify a different one of said plurality of diverse consistency levels for query transactions against each of said replicated databases; and

thereafter, automatically maintaining said specified one of said plurality of diverse consistency levels between said primary database and each of said replicated databases in response to updates to records within said primary database wherein queries requiring less than a full consistency level may be applied to a replicated database maintained at less than a full consistency level.

2. The method for enhanced efficiency in database access within a distributed data processing system according to claim 1, further including the step of replicating said primary database at a third physical location within said distributed data processing system.

3. A system for enhanced efficiency in database access within a distributed data processing system, said system comprising:

a primary database within said distributed data processing system, said primary database having a plurality of records stored therein;

a replica of said primary database stored at at least two physical locations within said distributed data processing system;

means for specifying a plurality of diverse consistency levels which may be maintained between said primary databases and each of said replicated databases;

means for permitting a user to specify a different one of said plurality of diverse consistency levels for query transactions against each of said replicated databases; and

means for automatically maintaining said specified one of said plurality of diverse consistency levels between said primary database and each of said replicated databases in response to updates to records within said primary database wherein queries requiring less than a full consistency may be applied to a replicated database maintained at less than a full consistency.

4. The system for enhanced efficiency in database access within a distributed data processing system according to claim 3, further including a second replica of said primary database stored at a third physical location within said distributed data processing system.