Propagating commit times

• US 20050050112A1
• Filed: 10/12/2004
• Published: 03/03/2005
• Est. Priority Date: 04/23/2003
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Chandrasekaran, Sashikanth
• Granted Patent: US 7,275,074 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/2322 using timestamps
• 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 707/99945 Object-oriented database structure processing
• 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 mechanism for propagating commit times between a plurality of database servers is provided. A database server maintains a set of one or more values that indicate which timestamps have been exchanged with at least one other database server that shares access to a common database. The one or more values maintained by the database server include a first value describing the most recent timestamp that the database server has sent to another database server and a second value describing the most recent timestamp that the database server has received from the other database server. The database server determines whether to send a commit timestamp associated with a committing transaction to another database server based, at least in part, on the set of one or more values. These techniques may be utilized for propagating commit times between any number of database servers.

Claims

1. A machine-implemented method, comprising:

maintaining, at a first server, a first value that reflects a most recent timestamp received from a second server; and

in response to the first server receiving a message that contains a timestamp from the second server, the first server performing the steps of;

determining whether the timestamp in the message reflects a time that is more recent than the time reflected by the first value, and

if the timestamp in the message reflects a time that is more recent than the time reflected by the first value, then updating the first value to reflect the timestamp in the message.

2. The method of claim 1, further comprising:

maintaining, at said first server, a set of values, wherein each of said set of values reflects a most recent timestamp received from a different server of a plurality of other servers.

3. The method of claim 1, wherein said first server and said second server are each database servers that have access to a common database.

4. The method of claim 1, further comprising:

in response to updating the first value, determining if a process exists, at said first server, which is waiting to commit a transaction until each server of a plurality of servers has a logical clock that reflects a time more recent than a commit time associated with said transaction.

5. The method of claim 4, further comprising:

in response to determining that said process exists, determining if said first value is more recent than said commit time.

6. The method of claim 5, further comprising:

if said first value is more recent than said commit time, then determining if the most recent message received from any other member of said plurality of servers is greater than the commit time of the transaction; and

if the most recent message received from any other member of said plurality of servers is greater than the commit time, then committing said transaction.

14. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 1.

15. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 2.

16. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 3.

17. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 4.

18. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 5.

19. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 6.

7. A machine-implemented method, comprising:

maintaining, at a first server, a first value that reflects a most recent timestamp sent to a second server; and

in response to the first server sending a message that contains a timestamp to the second server, the first server performing the steps of;

determining whether the timestamp in the message reflects a time that is more recent than the time reflected by the first value, and

if the timestamp in the message reflects a time that is more recent than the time reflected by the first value, then updating the first value to reflect the timestamp in the message.

8. The method of claim 7, further comprising:

maintaining, at said first server, a set of values, wherein each of said set of values reflects a most recent timestamp sent to a different server of a plurality of other servers.

9. The method of claim 7, wherein said first server and said second server are each database servers that have access to a common database.

20. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 7.

21. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 8.

22. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 9.

10. A machine-implemented method, comprising:

maintaining, at a first server, a first value that reflects a most recent timestamp received from a second server;

maintaining, at said first server, a second value that reflects a most recent timestamp sent to said second server; and

in response to committing a transaction, at said first server, the first database server determining whether to send a commit timestamp associated with said transaction to said second server based on said first value or said second value.

11. The method of claim 10, wherein said step of determining whether to send said commit timestamp comprises:

determining whether said first value or said second value reflects a time that is at least as recent as the time reflected by said commit timestamp.

12. The method of claim 10, further comprising the steps of:

transmitting said commit timestamp to said second server; and

if said commit timestamp reflects a time more recent than said second value, then updating said second value to reflect said commit timestamp.

13. The method of claim 12, further comprising:

in response to receiving said commit timestamp at said second server, transmitting an acknowledgement message to the first server only if a third value maintained at said second server is less recent than the commit timestamp,

wherein said third value reflects a most recent timestamp sent to said first server.

23. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 10.

24. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 11.

25. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 12.

26. A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 13.