Distributed database using indexed into tags to tracks events according to type, update cache, create virtual update log on demand

• US 5,924,096 A
• Filed: 10/15/1997
• Issued: 07/13/1999
• Est. Priority Date: 10/15/1997
• Status: Expired due to Term

• Current Assignee: Micro Focus Software, Inc. (Open Text Corporation)
• Original Assignee: Novell Incorporated (Open Text Corporation)
• Inventors: Lowry, Dale A, Draper, Stephen PW
• Primary Examiner(s): Amsbury, Wayne
• Assistant Examiner(s): CHANNAVAJJALA, SRIRAMA T
• Application Number:
  US08/950,575
• Time in Patent Office: 636 Days
• Field of Search: 707/1, 707/2, 707/3, 707/4, 707/5, 707/6, 707/7, 707/8, 707/10, 707/100, 707/102, 707/103, 707/200, 707/201, 707/202, 707/203, 707/204, 707/501, 707/511, 707/513, 707/514, 707/9, 707/101, 707/10 4
• US Class Current: 1/1
• 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: G06F 16/275 Synchronous replication
• CPC Class Codes: Y10S 707/99932 Access augmentation or optimizing
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

Methods and systems are provided for synchronizing local copies of a distributed database, such as a master copy and a partial copy stored in a replica or in a cache. Each data item in the database has an associated timestamp or other tag. An index into the tags in maintained. The tag index may be used to create an event list to reduce the time and bandwidth needed to synchronize the local copies. The tag index may also be used to create a virtual update log, thereby removing the need to maintain one or more physical logs recording the history of the copies.

Claims

1. A method for managing a distributed database of data items, including the computer-implemented steps of associating tags with at least some of the data items in the database, the tags determining the relative order of at least two operations on data items in the database;

in a local copy of the database, updating the tag for a given data item; and

maintaining an index into the tags for the local copy.

2. The method of claim 1, wherein database operations are categorized by event type, and the index into the tags can be used to quickly determine what events occurred after the event corresponding to a given tag value.

3. The method of claim 2, further including the computer-implemented step of using the index to create a list of recent events.

4. The method of claim 3, further comprising the computer-implemented step of using the list of recent events to update a cache containing at least one of the database data items.

5. The method of claim 4, wherein the cache is updated in response to a request to access the cache.

6. The method of claim 4, wherein the cache is updated periodically by a cache manager, regardless of any requests to access the cache.

7. The method of claim 4, wherein the updating step comprises receiving a token from a master system, the token representing the most recent event returned from the master system during a prior cache update.

8. The method of claim 3, wherein the list of recent events is constrained by event type, so an event appears in the list only if the event is of one or more selected event types.

9. The method of claim 3, wherein the list of recent events is constrained by number, so that not more than a predetermined maximum number of events appears in the list.

10. The method of claim 1, wherein the tags are updated whenever a database operation is performed on the given data item so that each tag value is no smaller than the largest tag value currently in the local copy of the database.

11. The method of claim 1, wherein the tags are updated to reflect a database operation when another local copy of the database requests synchronization with the local copy containing the tags.

12. The method of claim 1, further including the step of using the index to create a dynamic update log.

13. The method of claim 12, further including the step of using the dynamic update log to synchronize two copies of the database with each other.

14. The method of claim 12, wherein the dynamic update log is used to handle clashes while synchronizing copies of the database.

15. The method of claim 12, wherein each tag also identifies which copy of the database the data item is located in, so that updates to a given copy can be grouped during synchronization.

16. A computer system comprising a collection of data items having associated tags for determining the relative order of two operations on a database replica, and an index into the tags.

17. The system of claim 16, wherein the data items reside in a hierarchical database.

18. The system of claim 16, wherein the data items comprise HTML documents.

19. The system of claim 16, wherein the tags include compound tags.

20. The system of claim 19, wherein each compound tag includes a database partition identifier and an update reference.

21. The system of claim 16, further comprising a synchronization means for synchronizing local copies of a database.

22. The system of claim 21, wherein the tags include compound tags and the synchronization means supports independent synchronization of separate partitions of the database.

23. The system of claim 21, wherein the synchronization means comprises means for updating a cache.

24. The system of claim 21, wherein the synchronization means comprises means for updating a replica.

25. The system of claim 21, wherein the synchronization means comprises means for creating an event list.

26. The system of claim 25, wherein the synchronization means comprises means for constraining membership in the event list.

27. The system of claim 25, wherein the synchronization means comprises means for creating a dynamic update log.

28. A computer storage medium having a configuration that represents data and instructions which will cause at least a portion of a computer system to perform method steps for managing a distributed database of data items, the method steps comprising associating tags with at least some of the data items in the database, the tags determining the relative order of operations on data items in the database;

in a local copy of the database, updating a tag for a given data item; and

maintaining an index into the tags.

29. The storage medium of claim 28, wherein the method steps further comprise the step of using the index to create a list of recent events.

30. The storage medium of claim 29, wherein the method steps further comprise the step of using the list of recent events to update a cache containing at least one of the database data items.

31. The storage medium of claim 28, wherein the method steps further comprise the step of using the index to create a dynamic update log.

32. The storage medium of claim 31, wherein the method steps further comprise the step of using the dynamic update log to synchronize two copies of at least part of the database with each other.