Method of logical database snapshot for log-based replication

• US 20030220935A1
• Filed: 04/17/2003
• Published: 11/27/2003
• Est. Priority Date: 05/21/2002
• Status: Abandoned Application

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Guzman, Raymond, Vivian, Stephen J.
• Application Number:
  US10/417,724
• Publication Number:
  US 20030220935A1
• Time in Patent Office: Days
• US Class Current: 707/102
• 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

Abstract

A method of logical database snapshot for log-based replication in described that need not incur a quiescence of an operational database. Baselines for the overall snapshot operation and for each table replication are recorded in such a way that subsequent log-based replication can distinguish which redo records to apply and which to discard. The baselines may be recorded as system change numbers negotiated according to a distributed protocol for synchronizing a sequence number, and records from the redo log are applied on the logical standby system based on the recorded system change numbers.

Claims

1. A method for providing a logical standby database system for a primary database system, comprising:

extracting a change number generated on a primary database system from a message transmitted between the primary database system and the logical standby database system in accordance with a protocol that synchronizes the change number between the primary database and the logical standby database;

establishing the change number extracted from the message as a baseline change number for a target table on the logical standby database system that corresponds to a source table on the primary database system; and

selectively applying a redo record for the source table transmitted from the primary database system to target table on the logical standby database system based upon the baseline change number and a change number of the redo record.

2. A method according to claim 1, further comprising:

issuing a lock request against the source table followed by an unlock request against the source table.

3. A method according to claim 1, wherein said applying the redo record includes:

determining whether the change number of the redo record is greater than the baseline change number; and

executing the redo record on the target table of the logical standby database system if the change number exceeds the baseline change number.

4. A method according to claim 3, wherein the change number in the message is captured while the primary database system is operational.

5. A method according to claim 1, wherein said establishing includes recording the extracted change number during an insert-select operation.

6. A computer-readable medium bearing instructions for supporting a logical standby database, said instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 1.

7. A method for providing a logical standby database system for a primary database system, comprising:

issuing a lock request against a source table on the primary database system followed by an unlock request against the source table;

capturing a change number generated on the primary database system while the primary database system is operational;

incorporating the change number in a message that is transmitted between the primary database system and the logical standby database system in accordance with a protocol that synchronizes the change number between the primary database and the logical standby database;

extracting the change number from the message transmitted to the logical standby database system;

recording the change number extracted from the message during an insert-select operation as a baseline change number for a target table on the logical standby database system that corresponds to the source table; and

selectively applying a redo record for the source table transmitted from the primary database system to target table on the logical standby database system based upon the baseline change number and a change number of the redo record by;

determining whether the change number of the redo record is greater than the baseline change number; and

executing the redo record on the target table of the logical standby database system if the change number exceeds the baseline change number.

8. A distributed database system, comprising:

a primary database system storing a source table and configured for;

capturing a change number generated on the primary database system while the primary database system is operational; and

incorporating the change number in a message that is transmitted between the primary database system and the logical standby database system in accordance with a protocol that synchronizes the change number between the primary database and the logical standby database; and

a logical standby database system in communication with the primary database system and configured for;

extracting the change number from the message transmitted to the logical standby database system;

establishing the change number extracted from the message as a baseline change number for a target table on the logical standby database system that corresponds to the source table; and

selectively applying a redo record for the source table transmitted from the primary database system to target table on the logical standby database system based upon the baseline change number and a change number of the redo record.

9. A distributed database system according to claim 8, wherein the primary database system is further configured for:

issuing a lock request against a source table on the primary database system followed by an unlock request against the source table.

10. A distributed database system according to claim 8, wherein the logical standby database system is further configured for:

recording the change number extracted from the message during an insert-select operation.

11. A distributed database system according to claim 8, wherein the logical standby database system is further configured for:

determining whether the change number of the redo record is greater than the baseline change number; and

executing the redo record on the target table of the logical standby database system if the change number exceeds the baseline change number.