Method and apparatus for peer-to-peer data replication

• US 5,806,075 A
• Filed: 01/14/1997
• Issued: 09/08/1998
• Est. Priority Date: 09/24/1993
• Status: Expired due to Term

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle Corporation
• Inventors: Jain, Sandeep, Daniels, Dean
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Alam, Hosain T.
• Application Number:
  US08/783,156
• Time in Patent Office: 602 Days
• Field of Search: 395/608, 395/609, 395/616, 395/617, 395/200.6, 707/8, 707/9, 707/200, 707/201
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/2097 maintaining the standby controller/processing unit updated initialisation or re-synchronisation thereof G06F11/1658 and subgroups
• 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 707/954 Relational
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

The present invention provides the ability to replicate modifications made at a local site to multiple remote sites in a peer-to-peer environment. Information regarding these replicated modifications (e.g., insert, delete, or update) are contained in a set of replication tables. Thus, modifications can be duplicated at other sites immediately after the original modification, or deferred until the remote site is available. The replication tables of the present invention include a transactions table, transaction nodes table, calls table, call nodes table, and an exceptions table. The present invention further provides a logic-oriented procedure-level replication. Procedure-level replication modifies a remote site based on the logical operations used to modify the data at the originating site. Procedure-level replication provides the ability to identify conflicting updates as well. Information concerning conflicts identified by the present invention can be retained in the replication tables. The information contained in the replication tables can be used immediately, or subsequently, to address any conflicts detected by the present invention. The present invention provides the ability to rollback any modifications made once a conflict is identified. Further, the present invention provides the ability to address these conflicts within an application program. The present invention provides a row-oriented replication. A trigger associated with a table queues deferred remote procedures. The remote procedures use the old and new values from the original modification to replicate the modification at remote sites and detect conflicting updates.

Claims

1. A computer-implemented method for peer-to-peer data replication comprising the steps of:

performing a first modification to a first data value in a first computer and a second modification to a second data value in a second computer, said first and second data values being consistent prior to said first and second modifications;

generating first modification information in said first computer that is indicative of said first modification and second modification information in said second computer that is indicative of said second modification;

communicating said first modification information from said first computer to said second computer in response to performing the first modification;

communicating said second modification information from said second computer to said first computer in response to performing said second modification; and

modifying during a first time interval said first data value in said first computer and said second data value in said second computer based on said second modification information and said first modification information, respectively, to restore consistency between said first and second data values, said first and second computers being operational throughout said first time interval.

2. The method of claim 1 wherein said step of performing a first modification to a first data value comprises the step of setting an indicator in said first computer to indicate that said first modification has been performed in said first computer.

3. The method of claim 1 wherein said step of performing a first modification and said step of modifying said second data value based on said first modification information precede said step of performing a second modification an said step of modifying said first data value based on said second modification information.

4. The method of claim 1 wherein said step of modifying said first data value and said second data value based on said second and first modification information comprises the step of identifying exceptional occurrences.

5. The method of claim 4 further comprising the step of storing said first modification information and information indicative of at least one of said exceptional occurrences in one or more tables.

6. The method of claim 5 wherein said step of storing said first modification information in one or more tables in a database comprises the step of queuing a plurality of database transactions in the one or more tables, the plurality of database transactions indicating operations necessary to replicate said step of performing a first modification to a first data value in a first computer.

7. The method of claim 5 wherein said step of storing said first modification information in one or more tables in a database comprises the step of storing an identification value in a transaction identification field of a transaction table, the identification value uniquely identifying the first modification to the first data value in the first computer.

8. The method of claim 5 wherein said step of storing said first modification information in one or more tables in a database comprises the step of storing information indicating a procedure executed to modify the first data value in the first computer.

9. The method of claim 5 wherein said step of storing said first modification information in one or more tables in a database comprises the step of storing information indicating a data value to replace the first data value.

10. The method of claim 4 wherein said step of modifying said first data value and said second data value based on said second modification information and said first modification information, respectively, comprises the step of executing a procedure to modify said first data value.

11. The method of claim 10 wherein said step of identifying exceptional occurrences is incorporated into execution of said procedure.

12. The method of claim 4 wherein said step of identifying exceptional occurrences comprises the step of determining whether said first and second data modifications conflict.

13. The method of claim 1 wherein said step of generating said first modification information further includes the steps of:

obtaining information regarding a logical unit of work;

obtaining information regarding a procedure for replicating said logical unit of work; and

obtaining information regarding a destination at which said procedure is to be performed.

14. The method of claim 13 wherein said step of obtaining information regarding a logical unit of work comprises the step of obtaining information regarding modification of a data value.

15. The method of claim 14 wherein said step of obtaining information regarding modification of a data value comprises the step of obtaining information regarding modification of a data value in a database.

16. The method of claim 13 further comprising the step of obtaining information regarding exceptional conditions raised during said first and second data modifications.

17. The method of claim 13 wherein said step of obtaining information regarding a destination at which said procedure is to be performed comprises the step of obtaining information identifying one of a plurality of networked computers at which said procedure is to be performed.

18. An apparatus for peer-to-peer data replication comprising:

means for performing a first modification to a first data value in a first computer and a second modification to a second data value in a second computer, said first and second data values being consistent prior to said first and second modifications;

means for generating first modification information in said first computer that is indicative of said first modification and second modification information in said second computer that is indicative of said second modification;

means for communicating said first modification information from said first computer to said second computer in response to performing the first modification;

means for communicating said second modification information from said second computer to said first computer in response to performing the second modification; and

means for modifying during a first time interval said first data value in said first computer and said second data value in said second computer based on said second modification information and said first modification information, respectively, to restore consistency between said first and second data values, said first and second computers being operational throughout said first time interval.

19. The apparatus of claim 18 wherein said means for performing said first data modification is a processor executing a procedure.

20. The apparatus of claim 19 wherein said procedure includes instructions which, when executed by said processor, cause said processor to identify and handle said exceptional occurrences.

21. The apparatus of claim 18 wherein said means for modifying said first data value and said second data value based on said second modification information and said first modification information, respectively, comprises means for identifying exceptional occurrences.

22. The method of claim 18 wherein said means for generating first modification information comprises:

means for obtaining information regarding a logical unit of work;

means for obtaining information regarding a procedure for replicating said logical unit of work; and

means for obtaining information regarding a destination at which said procedure is to be performed.

23. The apparatus of claim 22 wherein said means for obtaining information regarding a logical unit of work comprises means for obtaining information regarding modification of a data value.

24. The apparatus of claim 22 further comprising means for obtaining information regarding exceptional conditions raised during said first and second data modifications.

25. An article of manufacture comprising a computer usable mass storage medium having computer readable program code embodied therein which, when executed by a first computer and a second computer, causes said first and second computers to perform computer-implemented peer-to-peer data replication, said computer readable program code in said article of manufacture comprising:

computer readable program code which, when executed by said first and second computers, causes said first computer to perform a first modification to a first data value stored in said first computer and said second computer to perform a second modification to a second data value stored in said second computer, said first and second data values being consistent prior to said first and second modifications;

computer readable program code which, when executed by said first and second computers, causes said first computer to generate first modification information indicative of said first modification and said second computer to generate second modification information indicative of said second modification;

computer readable program code which, when executed by said first and second computers, causes said first computer to communicate said first modification information to said second computer in response to performing the first modification and said second computer to communicate said second modification information to said first computer in response to performing the second modification; and

computer readable program code which, when executed by said first and second computers, causes said first and second computers to modify during a first time interval said first data value and said second data value based on said second modification information and said first modification information, respectively, to restore consistency between said first and second data values, said first and second computers being operational throughout said first time interval.

26. The article of claim 25 wherein said computer readable program code for causing said first and second computers to modify said first data value and said second data value based on said second modification information and said first modification information, respectively, comprises computer readable program code which, when executed by said first computer, causes said first computer to identify exceptional occurrences.

27. The article of claim 26 further comprising computer readable code which, when executed by said first computer, causes said first computer to store said first modification information and information indicative of at least one of said exceptional occurrences in one or more database tables.

28. The article of claim 25 wherein said computer readable program code causing said first computer to perform a first modification to a first data value comprises computer readable program code which, when executed by said first computer, causes said first computer to set an indicator in said first computer to indicate that said first modification has been performed in said first computer.

29. A method for maintaining duplication between a first data value and a second data value stored in respective first and second computers, the first and second computers remaining operational throughout a time interval over which said method is performed, said method comprising the computer-implemented steps of:

modifying the first data value so that the first data value is different from the second data value;

communicating to the second computer information indicative of said step of modifying the first data value in response to said step of modifying the first data value;

receiving in the second computer the information indicative of said step of modifying the first data value;

modifying the second data value to duplicate the first data value in response to said step of receiving in the second computer;

modifying the second data value so that the second data value is different from the first data value;

communicating to the first computer information indicative of said step of modifying the second data value so that the second data value is different from the first data value, said step of communicating to the first computer being in response to said step of modifying the second data value so that the second data value is different;

receiving in the first computer the information indicative of said step of modifying the second data value; and

modifying the first data value to duplicate the second data value in response to said step of receiving in the first computer.

30. A computer-implemented method for peer-to-peer data replication comprising the steps of:

storing first and second copies of a first data value in respective first and second computers, each copy of the first and second copies of the first data value being modifiable prior to modification of the other copy of the first and second copies of the first data value;

performing a modification to any one of the first and second copies of the first data value to produce a second data value in a respective one of the first and second computers;

communicating modification information indicative of said modification from the respective one of the first and second computers to the other computer of the first and second computers in response to said modification; and

modifying the remaining copy of the first and second copies of the first data value to produce a copy of the second data value in the other computer based on the modification information.

31. The method of claim 30 further comprising the step of storing modification information in one or more tables in a database, said modification information being indicative of said step of performing a modification to any one of the first and second copies of the first data value.

32. The method of claim 31 wherein said step of storing modification information in one or more tables in a database comprises the step of queuing a plurality of database transactions in the one or more tables, the plurality of database transactions indicating operations necessary to replicate said step of performing a modification to any one of the first and second copies of the first data value.

33. The method of claim 31 wherein said step of storing modification information in one or more tables in a database comprises the step of storing an identification value in a transaction identification field of a transaction table, the identification value uniquely identifying the modification to any one of the first and second copies of the first data value.

34. The method of claim 31 wherein said step of storing modification information in one or more tables in a database comprises the step of storing information indicating a procedure executed to modify any one of the first and second copies of the first data value.

35. The method of claim 31 wherein said step of storing modification information in one or more tables in a database comprises the step of storing information indicating the second data value.

36. The method of claim 30 wherein said step of modifying the remaining copy of the first and second copies based on the modification information comprises the step of identifying one or more exceptional occurrences.

37. The method of claim 36 further comprising the step of storing in one or more tables the modification information and information indicative of the one or more exceptional occurrences.

38. The method of claim 30 wherein said step of modifying the remaining copy of the first and second copies based on the modification information comprises the step of executing a procedure to modify the remaining copy of the first and second copies of the first data value.

39. A computer system for peer-to-peer data replication, said computer system comprising:

means for storing first and second copies of a first data value in respective first and second computers of said computer system, each copy of the first and second copies of the first data value being modifiable prior to modification of the other copy of the first and second copies of the first data value;

means for performing a modification to any one of the first and second copies of the first data value to produce a second data value in a respective one of the first and second computers;

means for communicating modification information indicative of said modification from the respective one of the first and second computers to the other computer of the first and second computers in response to said modification; and

means for modifying the remaining copy of the first and second copies of the first data value to produce a copy of the second data value in the other computer based on the modification information.

40. An article of manufacture comprising a computer-usable mass storage medium having computer readable program code embodied therein which, when executed by a first computer and a second computer, causes the first and second computers to perform computer-implemented peer-to-peer data replication by performing the steps of:

storing first and second copies of a first data value in the first and second computers, respectively, each copy of the first and second copies of the first data value being modifiable prior to modification of the other copy of the first and second copies of the first data value;

performing a modification to any one of the first and second copies of the first data value to produce a second data value in a respective one of the first and second computers;

communicating modification information indicative of said modification from the respective one of the first and second computers to the other computer of the first and second computers in response to said modification; and

modifying the remaining copy of the first and second copies of the first data value to produce a copy of the second data value in the other computer based on the modification information.

41. A computer-implemented method for peer-to-peer data replication comprising the steps of:

storing a plurality of copies of a first data value in respective computers of a plurality of networked computers, each copy of the plurality of copies of the first data value being modifiable prior to modification of the others of the plurality of copies of the first data value;

performing a modification to any one of the plurality of copies of the first data value to produce a second data value in a respective one of the plurality of networked computers;

storing in a transaction table modification information indicating one or more database transactions executed to perform said modification, the transaction table including a transaction identifier field storing information uniquely identifying each of the one or more database transactions executed;

storing in a nodes table information indicating at least one other computer of the plurality of networked computers at which the one or more database transactions are to be executed;

communicating the modification information stored in the transaction table to each of the computers indicated by the information stored in the nodes table in response to said modification; and

modifying remaining copies of the plurality of copies of the first data value to produce copies of the second data value based on the modification information.

42. A method for peer-to-peer data replication comprising the steps of:

storing first and second copies of a first data value in respective first and second computers, each copy of the first and second copies of the first data value being modifiable prior to modification of the other copy of the first and second copies of the first data value;

performing a modification to any one of the first and second copies of the first data value to produce a second data value in a respective one of the first and second computers;

communicating information that identifies a procedure for performing said modification from the respective one of the first and second computers to the other computer of the first and second computers; and

executing the procedure in the other computer to modify the remaining copy of the first and second copies of the first data value to produce a copy of the second data value.

43. The method of claim 42 wherein the step of communicating information that identifies a procedure includes the step of executing a remote procedure call in the respective one of the first and second computers to invoke the procedure in the other computer.

44. The method of claim 42 further comprising the step of communicating to the other computer parameters that are used as arguments to the procedure when the procedure is executed.

45. The method of claim 42 further comprising the step comparing at least one of the parameters to the remaining copy of the first and second copies of the first data value to confirm that the first and second copies of the first data value were consistent prior to said step of performing a modification.

46. An article of manufacture comprising a computer-usable mass storage medium having computer readable program code embodied therein which, when executed by a first computer and a second computer, causes the first and second computers to perform peer-to-peer data replication by performing the steps of:

storing first and second copies of a first data value in the first and second computers, respectively, each copy of the first and second copies of the first data value being modifiable prior to modification of the other copy of the first and second copies of the first data value;

performing a modification to any one of the first and second copies of the first data value to produce a second data value in a respective one of the first and second computers;

communicating information that identifies a procedure for performing said modification from the respective one of the first and second computers to the other computer of the first and second computers; and

executing the procedure in the other computer to modify the remaining copy of the first and second copies of the first data value to produce a copy of the second data value.

47. The article of claim 46 wherein the step of communicating information that identifies a procedure includes the step of executing a remote procedure call in the respective one of the first and second computers to invoke the procedure in the other computer.