Method of capturing a physically consistent mirrored snapshot of an online database

• US 6,877,016 B1
• Filed: 09/13/2001
• Issued: 04/05/2005
• Est. Priority Date: 09/13/2001
• Status: Active Grant

• Current Assignee: Unisys Corporation
• Original Assignee: Unisys Corporation
• Inventors: Hart, Donald Ralph, Lin, Kung Yi
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): NGUYEN, MERILYN P
• Application Number:
  US09/951,996
• Time in Patent Office: 1,300 Days
• Field of Search: 707/10, 707/201, 707/202, 707/203, 707/204, 707/8, 711/162
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1458 Management of the backup or restore process
• CPC Class Codes: G06F 11/1466 to make the backup process non-disruptive
• CPC Class Codes: G06F 2201/80 Database-specific techniques
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

An on-line primary database is momentarily QUIESCED to enable a physically consistent snapshot of the primary database to be mirrored to a secondary database as a backup while allowing the primary database to continue on servicing multiple user applications.

Claims

1. A method for developing a physically consistent snapshot at a secondary database of a primary database comprising the steps of:

(a) periodically flushing buffer memories having modified data onto said primary database, and including the step of;

(a1) initiating a DMUTILITY program command (QUIESCE) for managing transfer of modified data to a primary database on a primary disk (D1);

(b) establishing a physically consistent body of data in said primary database which is consistent with said buffered memories at a selected point in time, without denying use of said database to multiple users of read-only transactions, and including the steps of;

(b1) momentarily postponing requests from user-applications (QUIESCING) until all ongoing transactions are completed after said initiation of said DMUTILITY program, and including the steps of;

(b1a) flushing, at a selected point in time, of all modified buffers to said primary database (QUIESCED);

(b1b) holding off all user requests momentarily until all modified data buffers, at said selected point in time, are flushed onto said primary database;

(c) mirroring, at said selected point in time, all data on said primary database onto a secondary database;

(d) splitting off said secondary database from said primary database to provide a snapshot-in-time, of said primary database, at the location of said secondary database.

2. A system for developing a physically consistent database at a secondary database at a given point in time, said physically consistent secondary database derived from a primary pool of data buffers and audit buffers at a primary database means comprising:

(a) multiple user applications connected to a database having a system memory means;

(b) said primary database means for servicing multiple user applications and interfacing a primary database disk means;

(c) said system memory means providing a primary pool of buffer memory units for holding modified data and for holding audit data;

(d) said primary database means including;

(d1) means for holding updated data on a first data disk;

(d2) means for holding audit data on an audit disk;

(d3) means for holding accumulated data on said first data disk;

(e) means for momentarily stopping access to said primary database means until all modified buffer memory units have been flushed to said primary database means to provide a physically consistent set of data on said primary database means at a given point in time, said given point in time being determined by a Database Control Point File means which includes;

(ei) means to initiate a QUIESCE command operation to flush all modified buffer data units to said primary database means;

(f) means to mirror the data of said primary database disk means onto a secondary database disk means during a QUIESCE operation to provide a physically consistent snapshot at said secondary database disk means, of the data from said primary database disk means;

(g) means to split off said secondary database disk means form said primary database disk means after completion of said QUIESCE command.

3. A method for developing a physically consistent snapshot at a secondary database of a primary database, comprising the steps of:

(a) initiating a DUMUTILITY QUIESCE command;

(b) allowing the completion of active transactions to said primary database;

suspending subsequent pending transactions;

(c) permitting the continuance of applications performing non-transactional read-only operations which are unaffected by said QUIESCE command;

(d) writing, from said primary database system memory to disk D1, all updated data buffers (11D) when all active transactions are completed;

(e) duplicating said primary database (D1) to obtain a physically consistent snapshot copy (D2).