Method of capturing a physically consistent mirrored snapshot of an online database
First Claim
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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.
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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.
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Citations
3 Claims
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1. A method for developing a physically consistent snapshot at a secondary database of a primary database comprising the steps of:
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(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.
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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:
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(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.
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3. A method for developing a physically consistent snapshot at a secondary database of a primary database, comprising the steps of:
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(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).
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Specification