System and method for reconciling transactions between a replication system and a recovered database

• US 20060212493A1
• Filed: 05/23/2006
• Published: 09/21/2006
• Est. Priority Date: 02/11/2000
• Status: Active Grant

• Current Assignee: Quest Software, Inc.
• Original Assignee: Eyal M. Aronoff, James W. Collings
• Inventors: Aronoff, Eyal M., Collings, James W.
• Granted Patent: US 7,461,103 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/178 Techniques for file synchronisation in file systems
• CPC Class Codes: G06F 16/2358 Change logging, detection, and notification replication G06F16/27
• CPC Class Codes: G06F 16/27 Replication, distribution or synchronisation of data between databases or within a distributed database system; Distributed database system architectures therefor
• CPC Class Codes: Y10S 707/99932 Access augmentation or optimizing
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

The invention is a reconcile system for providing data replication between a source system and a target system. The reconcile system includes a reconcile process that determines a recovery position for a failed or otherwise desynchronized target system, and purges queues of the reconcile system of stale transactions occurring before the recovery position, thereby ensuring synchronization between the source and target systems.

Claims

1. A system for performing replication between a source device and a target device, the system comprising:

a source database having first data files and log files storing replication transactions corresponding to changes made to the first data files;

a recovered target database having second data files comprising data associated with at least one replication transaction stored in the log files; and

a replication device capable of replicating at least a portion of the first data files to the recovered target database by posting to the recovered target database the changes made to the first data files, the replication device comprising;

at least one poster queue configured to store information indicative of the replication transactions, and

a reconcile process configured to purge at least one replication transaction from the at least one poster queue when the at least one replication transaction has already been applied to the recovered target database.

2. The system of claim 1, wherein the second data files comprise a rolled back copy of at least a portion of the first data files.

3. The system of claim 2, wherein the replication device is configured to perform the replication transactions by rolling forward at least a portion of information rolled back during recovery of the recovered target database.

4. The system of claim 3, wherein the replication device is further configured to perform the replication transactions such that the at least one replication transaction purged from the at least one poster queue is not applied while rolling forward.

5. The system of claim 1, wherein the source database remains available during recovery of the recovered target database.

6. The system of claim 1, wherein the replication device further comprises at least one poster process configured to read the information stored in the at least one poster queue, the at least one poster process configured to generate commands interpretable by the recovered target database and designed to change the recovered target database to reflect the changes made to the first data files.

7. The system of claim 6, wherein the at least one poster process is configured to read a completion indicator from the at least one poster queue, wherein the completion indicator corresponds to one or more finalized changes made to the source database.

8. The system of claim 7, wherein the completion indicator corresponds to a COMMIT statement.

9. The system of claim 1, wherein the reconcile process employs a plurality of placement indicators to determine which information stored in the poster queues is stale.

10. The system of claim 9, wherein one of the plurality of placement indicators corresponds to a recovery marker placed by the recovered target database, wherein the recovery marker identifies how much of the information the recovered target database already applied during recovery thereof.

11. A method of recovering or instantiating a target database during replication from a source database to the target database, the method comprising:

logging replication transactions in a replication system, wherein the replication transactions are associated with changes made to a source database;

applying the replication transactions to a target database to maintain in the target database a copy of the source database;

recovering the target database by rolling back information applied to the target database such that the recovered target database contains a copy of certain changes represented by the replication transactions contained in the replication system; and

purging the replication transactions from the replication system that represent the certain changes already applied to the recovered target database.

12. The method of claim 11, additionally comprising restarting replication by rolling forward at least some of the information rolled back during said recovering of the target database such that the purged stale replication transactions are not applied during replication.

13. The method of claim 12, wherein the source database remains available during said recovering, purging, and restarting.

14. The method of claim 13, additionally comprising creating in the target database a copy of the source database by employing a hot backup mode of a database management system of the source database.

15. The method of claim 13, wherein said recovering the target database comprises placing a recovery marker in the recovered copy, thereby identifying a recovery position therein.

16. The method of claim 15, wherein said purging the replication transactions comprises locating the recovery marker and the replication transactions representing certain changes completed on the source system before the placement of the recovery marker.

17. A replication system for reconciling information stored in a replication device with a recovered database, the replication system comprising:

first means for storing data files and log files, wherein the log files store replication transactions corresponding to changes made to the data files;

second means for storing a rolled back copy of the data files after recovery of the second means, wherein the rolled back copy of the data files comprises data associated with at least one replication transaction stored in the log files; and

means for replicating at least a portion of the data files to the second means by posting to the second means the changes made to the data files, the means for replicating comprising;

means for storing information indicative of the replication transactions, and

means for purging at least one replication transaction from the means for storing information when the at least one replication transaction has already been applied to the second means.

18. The replication system of claim 17, wherein the means for replicating is configured to perform the replication transactions by rolling forward at least a portion of information rolled back during recovery of the second means.

19. The replication system of claim 18, wherein the means for replicating is further configured to perform the replication transactions such that the at least one replication transaction purged from the means for storing information is not applied while rolling forward.

20. The replication system of claim 17, wherein the first means remains available during recovery of the second means.