Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-05-07
2001-01-23
Black, Thomas G. (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000, C707S793000
Reexamination Certificate
active
06178427
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to database management systems, in particular to systems and methods of mirroring database log data.
BACKGROUND OF THE INVENTION
Methods and systems are known for creating and maintaining backup copies of a primary database which can be used in place of the primary database should the primary database become unavailable. The backup and primary databases are typically maintained on separate systems at remote locations, to reduce the possibility that a disruptive event will affect both databases. Changes made to the primary database are typically logged and then applied to the backup database to keep the backup database up-to-date with the primary database. Furthermore, the logged changes can also be re-applied to the primary database to recover from a disaster affecting the primary database. Like the backup system, the change logs are typically shipped to and kept at a location remote from the primary system.
Important considerations in disaster recovery planning with regard to any database management system (DBMS) such as DB
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(from International Business Machines of Armonk, New York) in which log records are used to rebuild the system, are how to get the log records offsite to a remote location and how often. Currently, a typical solution is to create copies of the log datasets and ship them to the remote site on some type of regular schedule, e.g., once a day. However, if a disaster should occur at the primary site hours after the logs are created and shipped offsite, a large amount of data may be lost, requiring re-entry of many transactions into the primary system.
In the case of recovering individual database objects, such as a DB
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tablespace, a major source of delay in the recovery process is the reading of the DB
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log. The log not only contains information for the tablespace being recovered, it also contains log information for the entire system including other objects which are not of interest. As a result, a large amount of unneeded data may be read in order to perform the recovery of a single tablespace.
Existing products such as R+/CHANGE ACCUM from BMC Software, Inc. of Houston, Tex. and MERGE/MODIFY from Platinum Technology, Inc. of Oakbrook Terrace, Ill., offer a mechanism to extract log data from the DB
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log to create proprietary datasets containing only the pertinent log data for one or more selected tablespaces. This can help eliminate unnecessary I/O operations. Nonetheless, these processes still need to be scheduled. This may still require that unneeded log datasets be read to catch any updates that were made since the last time the proprietary datasets were created.
SUMMARY OF THE INVENTION
The present invention provides a method and system for creating and maintaining mirror log datasets in real time.
The present invention also provides a method of automatically performing gap recovery and a mechanism to create, in real time, standardized (e.g. DB
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compliant) log datasets or proprietary log datasets which contain log data pertaining to one or more selected objects, such as tablespaces. The selected objects for which log mirroring is performed can be in the same source database or in different source databases.
In accordance with an embodiment of the present invention, a mirroring transaction processing task is started on each of a local and a remote site. A user request to initiate mirroring of log datasets is sent to the remote task. In response, the remote task obtains information from the local DBMS to determine the size of the new log datasets which are to mirror the original log datasets and allocates the new datasets accordingly. The remote task then requests both archived and active log data from the local DBMS. Upon receiving the requested log data, the remote task passes the log data to a formatting routine in which the raw log data is written, for example, to a new DB
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log dataset or to a proprietary dataset. If there is a gap in the log data, then gap recovery is performed. If there is an error in writing log data to the dataset, the remote task determines whether a new dataset is needed, and if so, defines the new dataset and rewrites the log data into the new dataset.
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patent: 5742792 (1998-04-01), Yanai et al.
patent: 5799141 (1998-08-01), Galipeau et al.
patent: 5901327 (1999-05-01), Ofek
patent: 5903898 (1999-11-01), Cohen et al.
patent: 6044444 (2000-03-01), Ofek
Baker & McKenzie
Black Thomas G.
Do Thuy
PLATINUM technology IP, Inc.
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