Capturing and re-creating the state of a queue when migrating a session

• US 20060059228A1
• Filed: 05/17/2005
• Published: 03/16/2006
• Est. Priority Date: 08/12/2004
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Liang, Chao, Kasamsetty, Ravikanth, Kaluskar, Sanjay H., Koti, Ravi
• Granted Patent: US 7,415,470 B2
• Time in Patent Office: Days
• US Class Current: 709/203
• CPC Class Codes: G06F 9/5088 involving task migration
• CPC Class Codes: G06F 9/546 Message passing systems or structures, e.g. queues
• CPC Class Codes: H04L 67/14 Session management for real-time applications in data packet communications networks H04L65/1066
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A method and apparatus for migrating the session state of an original session from a first node to a second node, such that a process, executing in the migrated session, may enqueue and dequeue messages from a queue of messages and experience the same behavior from the queue of messages as if the process was enqueuing and dequeuing messages in the original session. Advantageously, all the benefits of migrating a session from one node to another node may be realized, even when the session contains queuing state information that describes the state of a queue of messages. Data that indicates how many messages one or more subscribers have removed from the queue of messages may also be stored to preserve proper behavior of the queue of messages for multiple subscribers when sessions are migrated.

Claims

1. A machine-implemented method, comprising:

receiving a request to migrate a session established on a first server to a second server, wherein the first session comprises queuing state information that describes the state of a queue of messages; and

migrating the queuing state information to the second server.

2. The method of claim 1, wherein the session is a first session, and further comprising the step of:

establishing a second session, on the second server, that has access to the queuing state information.

3. The method of claim 1, wherein the session is a first session, and further comprising:

migrating a user connected through the first session to a second session that has access to the queuing state information.

4. The method of claim 1, wherein the step of migrating the queuing state information to the second server comprises:

transmitting, from the first server to the second server, a migrate time, wherein the migrate time reflects the sum of the current system time of the first server and a delta value,

wherein, if the first session was previously migrated from a third server to the first server, then the delta value reflects a difference between the logical clocks of the third server and the first server at the time the first session was migrated from the third server to the first server, and

wherein, if the first session was not previously migrated from a third server to the first server, then the delta value has a value of zero.

5. The method of claim 4, wherein the step of migrating the queuing state information to the second server further comprises:

receiving, at the second server, the migrate time; and

determining a recalculated delta value, wherein;

if the migrate time is more recent than the current system time of the second server, then the recalculated delta value is equal to the difference between the migrate time and the current system time of the second server; and

if the migrate time is not more recent than the current system time of the second server, then the recalculated delta value has a value of zero.

6. The method of claim 5, wherein the step of migrating the queuing state information to the second server further comprises:

obtaining a message enqueue time for a particular message, wherein the message enqueue time reflects the sum of the recalculated delta value and the current system time of the second server; and

adding the particular message to the second queue of messages using the message enqueue time.

7. The method of claim 1, wherein the step of migrating the queuing state information to the second server comprises:

determining if a dequeue operation is of a first type or a second type;

if said dequeue operation is of the first type, then transmitting, from the first server to the second server, information identifying (a) the operation, (b) a number of messages that have already been dequeued from the first queue of messages, and (c) a logical time associated with the operation; and

if said dequeue operation is of the second type, then transmitting, from the first server to the second server, information identifying the messages, and their relative order, that have not been dequeued from the first queue of messages.

8. The method of claim 7, wherein said information identifying the messages, and their relative order, that have not been dequeued from the first queue of messages is maintained in a LOB.

9. The method of claim 1, wherein the first server and the second server are both database servers.

10. The method of claim 1, wherein the queue of messages is implemented in a database.

11. The method of claim 1, further comprising the steps of:

storing, at the second server, dequeue data that indicates how many messages each of two or more users have removed from the second queue of messages; and

determining how to process a request to dequeue an message from the second queue of messages based on the dequeue data.

12. A machine-readable medium carrying one or more sequences of instructions, wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to perform the steps of:

receiving a request to migrate a session established on a first server to a second server, wherein the first session comprises queuing state information that describes the state of a queue of messages; and

migrating the queuing state information to the second server.

13. The machine-readable medium of claim 12, wherein the session is a first session, and wherein execution of the one or more sequences of instructions by the one or more processors causes the one or more processors to further perform the step of:

establishing a second session, on the second server, that has access to the queuing state information.

14. The machine-readable medium of claim 12, wherein the session is a first session, and wherein execution of the one or more sequences of instructions by the one or more processors causes the one or more processors to further perform the step of:

migrating a user connected through the first session to a second session that has access to the queuing state information.

15. The machine-readable medium of claim 12, wherein the step of migrating the queuing state information to the second server comprises:

transmitting, from the first server to the second server, a migrate time, wherein the migrate time reflects the sum of the current system time of the first server and a delta value,

wherein, if the first session was previously migrated from a third server to the first server, then the delta value reflects a difference between the logical clocks of the third server and the first server at the time the first session was migrated from the third server to the first server, and

wherein, if the first session was not previously migrated from a third server to the first server, then the delta value has a value of zero.

16. The machine-readable medium of claim 15, wherein the step of migrating the queuing state information to the second server further comprises:

receiving, at the second server, the migrate time; and

determining a recalculated delta value, wherein;

if the migrate time is more recent than the current system time of the second server, then the recalculated delta value is equal to the difference between the migrate time and the current system time of the second server; and

if the migrate time is not more recent than the current system time of the second server, then the recalculated delta value has a value of zero.

17. The machine-readable medium of claim 16, wherein the step of migrating the queuing state information to the second server further comprises:

obtaining a message enqueue time for a particular message, wherein the message enqueue time reflects the sum of the recalculated delta value and the current system time of the second server; and

adding the particular message to the second queue of messages using the message enqueue time.

18. The machine-readable medium of claim 12, wherein the step of migrating the queuing state information to the second server comprises:

determining if a dequeue operation is of a first type or a second type;

if said dequeue operation is of the first type, then transmitting, from the first server to the second server, information identifying (a) the operation, (b) a number of messages that have already been dequeued from the first queue of messages, and (c) a logical time associated with the operation; and

if said dequeue operation is of the second type, then transmitting, from the first server to the second server, information identifying the messages, and their relative order, that have not been dequeued from the first queue of messages.

19. The machine-readable medium of claim 18, wherein said information identifying the messages, and their relative order, that have not been dequeued from the first queue of messages is maintained in a LOB.

20. The machine-readable medium of claim 12, wherein the first server and the second server are both database servers.

21. The machine-readable medium of claim 12, wherein the queue of messages is implemented in a database.

22. The machine-readable medium of claim 12, wherein execution of the one or more sequences of instructions by the one or more processors causes the one or more processors to further perform the steps of:

storing, at the second server, dequeue data that indicates how many messages each of two or more users have removed from the second queue of messages; and

determining how to process a request to dequeue an message from the second queue of messages based on the dequeue data.