Method and system for detecting conflicts in replicated data in a database network

• US 20030182319A1
• Filed: 03/25/2002
• Published: 09/25/2003
• Est. Priority Date: 03/25/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Morrison, Michael
• Granted Patent: US 7,149,759 B2
• Time in Patent Office: Days
• US Class Current: 707/200
• CPC Class Codes: G06F 16/273 Asynchronous replication or reconciliation
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A method and system for detecting conflicts in replicated data in a database network is disclosed. The database network includes a plurality of computer systems, each having a table which includes replicated data. According to the method and system of the present invention, a column is provided to the table in each system which indicates whether replicated data in the table is current for the system. The method and system further includes determining whether replicated data in the table in the system is current based on a value in the column when a request to access the replicated data in the table is received.

Through aspects of the method and system of the present invention, conflict detection is delayed until a request to access the replicated data in the system is submitted. Thus, no conflict detection is required during the replication cycle, nor is any conflict resolution required during the replication cycle. In an environment with many thousands or millions of rows being replicated, but with few actual conflicts, delaying the detection and resolution until the system actually accesses the replicated data greatly improves the overall performance of the replication environment.

Claims

1. A method for detecting conflicts in replicated data in a database network, wherein the database network includes a plurality of systems, each system including a table which includes replicated data, the method comprising the steps of:

(a) providing a column to the table in each of the plurality of systems which indicates whether the replicated data in the table is current; and

(b) determining whether the replicated data in the table in one of the plurality of systems is current based on the column when a request to access the replicated data in the table is received.

2. The method of claim 1, wherein the providing step (a) further includes the step of:

(a1) defining a structured data type for a value in the column, wherein the structured data type is a binary large object (BLOB).

3. The method of claim 1, wherein the providing step (a) further includes the steps of:

(a1) defining a structured array data type for a value in the column, wherein the structured array includes a plurality of elements and each element is associated with replicated data stored in a column in a given row in the table; and

(a2) assigning a value to each element, wherein the value indicates whether the replicated data stored in the associated column and the given row is current.

4. The method of claim 3, wherein the value of the element is one of a null value, a local value, and an identifier.

5. The method of claim 4, wherein the determining step (b) further includes the steps of:

(b1) checking the value of the element associated with the requested replicated data;

(b2) determining that the requested replicated data is current if the value of the element is one of a null value and a local value; and

(b3) determining that the requested replicated data is not current if the value is an identifier, wherein the identifier identifies a second system in the database network that has the current value for the requested replicated data.

6. The method of claim 1 further including the step of:

(c) obtaining a current value of the requested replicated data if the requested replicated data in the one system is not current.

7. The method of claim 6, wherein the obtaining step (c) further includes the steps of:

(c1) contacting a second system identified by a value in the column;

(c2) requesting from the second system the current value of the replicated data; and

(c3) transmitting the current value of the replicated data from the second system to the one system.

8. The method of claim 7, wherein the obtaining step (c) further includes the step of:

(c4) updating, in the table in the second system, the value in its column to an identifier identifying the one system.

9. The method of claim 7, wherein the obtaining step (c) further includes the steps of:

(c4) checking, in the table in the second system, the value in its column to determine whether the requested replicated data in the second system is current;

(c5) obtaining the current value of the requested replicated data from a third system identified by the value in the column if the requested replicated data in the second system is not current; and

(c6) repeating steps (c4) and (c5) in successive systems until the current value of the requested replicated data is found.

10. The method of claim 6 further including the steps of:

(d) updating the requested replicated data with the current value;

(e) changing the value in the column to indicate that the replicated data is current; and

(f) returning the current value of the requested replicated data for further processing.

11. A computer usable medium containing programming instructions for detecting conflicts in replicated in a database network, wherein the database network includes a plurality of systems, each system including a table which includes replicated data, the programming instructions for:

(a) providing a column to the table in each of the plurality of systems which indicates whether the replicated data in the table is current;

(b) determining whether the replicated data in the table in one of the plurality of systems is current based on the column when a request to access the replicated data in the table is received.

12. The computer usable medium of claim 11, wherein the providing instruction (a) further includes the instructions for:

(a1) defining a structured data type for the value in the column, wherein the structured data type is a binary large object (BLOB).

13. The computer usable medium of claim 11, wherein the providing instruction (a) further includes the instructions for:

(a1) defining a structured array data type for the value in the column, wherein the structured array includes a plurality of elements and each element is associated with replicated data stored in a column in a given row in the table; and

(a2) assigning a value to each element, wherein the value indicates whether the replicated data stored in the associated column and the given row is current.

14. The computer usable medium of claim 13, wherein the value of the element is one of a null value, a local value, and an identifier.

15. The computer usable medium of claim 14, wherein the determining instruction (b) further includes the instructions for:

(b1) checking the value of the element associated with the requested replicated data;

(b2) determining that the requested replicated data is current if the value of the element is one of a null value and a local value; and

(b3) determining that the requested replicated data is not current if the value is an identifier, wherein the identifier identifies a second system in the database network that has the current value for the requested replicated data.

16. The computer usable medium of claim 11 further including the instruction for:

(c) obtaining a current value of the requested replicated data if the requested replicated data in the one system is not current.

17. The computer usable medium of claim 16, wherein the obtaining instruction (c) further includes the instructions for:

(c1) contacting a second system identified by a value in the column;

(c2) requesting from the second system the current value of the replicated data; and

(c3) transmitting the current value of the replicated data from the second system to the one system.

18. The computer usable medium of claim 17, wherein the obtaining instruction (c) further includes the instructions for:

(c4) updating, in the table in the second system, the value in its column to an identifier identifying the one system.

19. The computer usable medium of claim 17, wherein the obtaining instruction (c) further includes the instructions for:

(c4) checking, in the table in the second system, the value in its column to determine whether the requested replicated data in the second system is current;

(c5) obtaining the current value of the requested replicated data from a third system identified by the value in the column if the requested data in the second system is not current; and

(c6) repeating steps (c4) and (c5) in successive systems until the current value of the requested replicated data is found.

20. The computer usable medium of claim 16 further including the instructions for:

(d) updating the requested replicated data with the current value;

(e) changing the value in the column to indicate that the replicated data is current; and

(f) returning the current value of the requested replicated data for further processing.

21. A system for detecting conflicts in replicated data in a database network, wherein the database network includes a plurality of computer systems, each computer system including a database management system (“

DBMS”

) and a table which includes replicated data, the system comprising;

a column appended to the table in each of the plurality of computer systems, wherein the column indicates whether replicated data in the table in the computer system is current; and

a conflict detection/resolution module in each of the plurality of computer systems coupled to the DBMS, wherein the conflict detection/resolution module in the computer system includes means for determining whether replicated data in the computer system is current based on the column when a request to access replicated data in the table is received.

22. The system of claim 21, wherein the column includes a plurality of elements structured in an array, wherein each element is associated with replicated data stored in an associated column in a given row in the table.

23. The system of claim 22, wherein the conflict detection/resolution module includes means for assigning a value to each element in the array, wherein the value indicates whether the replicated data stored in the associated column and the given row is current.

24. The system of claim 21, wherein the conflict detection/resolution module further includes means for obtaining a current value of the requested replicated data if the requested replicated data in the computer system is not current.

25. The system of claim 24, wherein the obtaining means includes:

means for contacting a second computer system identified by a value in the column;

means for requesting from the second computer system the current value of the replicated data; and

means for receiving the current value of the replicated data from the second computer system.

26. The system of claim 24, wherein the conflict detection/resolution module further includes:

means for updating the requested replicated data with the current value;

means for changing the value in the column to indicate that the replicated data is current; and

means for returning the current value of the requested replicated data for further processing.

27. The system of claim 21, wherein the conflict detection/resolution module further includes:

means for receiving a request for replicated data in the table from a requesting computer system in the database network; and

means for transmitting the replicated data to the requesting computer system if the replicated data is current.

28. A method for resolving conflicts in replicated data in a peer-to-peer database network, wherein the database network includes a plurality of members, each member including a table which includes replicated data, the method comprising the steps of:

(a) adding a conflict detection indicator column to the table in each member, wherein the conflict detection indicator column indicates whether replicated data in the table is current;

(b) examining a value in the conflict detection indicator column to determine whether replicated data in the table in a first member is current when a request to access replicated data in the table is received;

(c) obtaining current replicated data from a second member identified by the value in the conflict detection indicator column if the replicated data in the table in the first member is not current;

(d) updating the replicated data in the first member with the current replicated data; and

(e) modifying the value in the conflict detection indicator column to indicate that the replicated data in the table in the first member is current.

29. The method of claim 28, wherein the adding step (a) further includes the steps of:

(a1) defining a structured array data type for the value in the conflict detection indicator column, wherein the structured array includes a plurality of elements and each element is associated with replicated data stored in an associated column in a given row in the table; and

(a2) assigning a value to each element, wherein the value is one of a null value, a local value, and an identifier.

30. The method of claim 29, wherein the examining step (b) further includes the steps of:

(b1) checking the value of the element associated with the requested replicated data;

(b2) determining that the requested replicated data is current if the value of the element is one of a null value and a local value; and

(b3) determining that the requested replicated data is not current if the value is an identifier, wherein the identifier identifies the second member in the database network that has the current value for the requested replicated data.

31. A computer usable medium containing programming instructions for resolving conflicts in replicated data in a peer-to-peer database network, wherein the database network includes a plurality of members, each member including a table which includes replicated data, the programming instructions for:

(a) adding a conflict detection indicator column to the table in each member, wherein the conflict detection indicator column indicates whether replicated data in the table is current;

(b) examining a value in the conflict detection indicator column to determine whether replicated data in the table in a first member is current when a request to access replicated data in the table is received;

(c) obtaining current replicated data from a second member identified by the value in the conflict detection indicator column if the replicated data in the table in the first member is not current;

(d) updating the replicated data in the first member with the current replicated data; and

(e) modifying the value in the conflict detection indicator column to indicate that the replicated data in the table in the first member is current.

32. The computer usable medium of claim 31, wherein the adding instruction (a) further includes the instructions for:

(a1) defining a structured array data type for the value in the conflict detection indicator column, wherein the structured array includes a plurality of elements and each element is associated with replicated data stored in an associated column in a given row in the table; and

(a2) assigning a value to each element, wherein the value is one of a null value, a local value, and an identifier.

33. The computer usable medium of claim 32, wherein the examining instruction (b) further includes the instructions for:

(b1) checking the value of the element associated with the requested replicated data;

(b2) determining that the requested replicated data is current if the value of the element is one of a null value and a local value; and

(b3) determining that the requested replicated data is not current if the value is an identifier, wherein the identifier identifies the second member in the database network that has the current value for the requested replicated data.