System and method for providing a backup copy of a database

• US 5,594,900 A
• Filed: 03/22/1995
• Issued: 01/14/1997
• Est. Priority Date: 12/02/1992
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Nagin, Kenneth, Winokur, Alex, Novick, Yoram, Cohn, Oded
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): PHAM, CUAN
• Application Number:
  US08/409,478
• Time in Patent Office: 664 Days
• Field of Search: 395/600, 395/575, 395/200, 395/700
• US Class Current: 1/1
• CPC Class Codes: G06F 11/2064 while ensuring consistency
• CPC Class Codes: G06F 11/2071 using a plurality of controllers
• CPC Class Codes: G06F 2201/80 Database-specific techniques
• CPC Class Codes: G11C 29/74 using duplex memories, i.e. using dual copies
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A backup method for a computer database system comprising maintaining a mirrored copy of the database at a remote location is characterized in that updates to the remote database data are delayed for a delay time greater than or equal to the upper limit on the data communication delay between the local location and the remote location and updates to a remote log for the database are executed after corresponding updates to a local log without said delay. In this way a consistent copy of the database may be recovered from the mirrored copy of the database and the remote log after destruction of the database system.

Claims

1. A backup method for a database having at least one application data set and at least one log data set stored and maintained at a local location by a computer system having a central processing unit (CPU) comprising:

maintaining a mirrored copy of the database at a remote location in communication with the local location characterized in that a writing of updates to a database application data set at the remote location is delayed for an extra delay time in addition to the delay time inherent in sending records to the remote location, so that a total delay time for writing updates to an application data set at the remote location is always at least as long as an upper limit on the data communication delay between the local location and the remote location and updates to a remote log data set for the database are executed after corresponding updates to a local log data set are executed without said extra delay time in addition to the delay time inherent in the sending of records to the remote location; and

recovering a consistent copy of the database from the mirrored copy of the database and the remote log data set after destruction of the database at the local location by executing the remote log entries against the remote database data starting from an entry in the remote log a number of entries back from the end of the remote log at least as great as the maximum number of log entries which may be written in said delay time.

2. A method as claimed in claim 1 wherein a confirmation of a successful update to the local log is performed prior to making a corresponding update to the remote log.

3. A method as claimed in claim 1 wherein a confirmation of a successful update to the local log is performed after having made a corresponding update to the remote log.

4. A data storage system connectable to and for use with a computer database system having database data stored in a portion of storage in the data storage system and a database log stored in a reserved portion of storage in the data storage system, the data storage system being in communication with a remote:

data storage system having a copy of the database data and the database log stored in portions of storage in the remote data storage system, the data storage system comprising;

logic means for executing a write instruction in the data storage system received from the computer database system;

logic means for communicating the write instruction from the data storage system to the remote data storage system for execution in the remote data storage system;

logic means for determining from the write instruction whether the write is to a portion of storage in the data storage system reserved for a database log;

logic means for delaying the initiation of the communication to the remote data storage system of a write instruction to a portion of storage in the remote data storage system not reserved for the database log for a time at least equal to the upper limit on the data communication delay between the data storage system and the remote data storage system; and

logic means for executing the write instructions communicated to the remote data storage system against the copy of the database data stored in the remote data storage system, so that a consistent copy of the database data is recoverable from the copy of the database data and the copy of the database log stored in the remote data storage system after destruction of the data storage system.

5. A data storage system as claimed in claim 4 in the form of a disk controller connectable to a host processor, at least one disk drive unit and a remote similar disk controller.

6. An article of manufacture comprising:

a computer usable medium having computer readable program code means embodied therein for backing up a database having at least one application data set and at least one log data set stored and maintained at a local location, comprising;

computer readable program code means for executing a write instruction at the local location;

computer readable program code means for communicating the write instruction from the local location to a remote location in communication with the local location database;

computer readable program code means for determining from the write instruction whether the write is to a log data set of the local location database;

computer readable program code means for delaying the initiation of the communication to the remote location of a write instruction to an application data set for a time at least equal to the upper limit on the data communication delay between the local location database and the remote location database; and

computer readable program code means for executing the write instructions communicated to the remote location against the copy of the application data set of the remote location database, so that a consistent copy of the local database is recoverable from the remote database after destruction of the local location database.