Session Queue State Capture for Database Migration
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Solution Overview
Problem
Existing techniques fail to preserve the queuing state information during session migration across nodes in multi-node database systems, leading to inconsistent behavior when enqueuing or dequeuing messages from a queue, as the session state describing the queue's state is not effectively transferred.
Innovation Solution
The proposed solution involves capturing and re-creating the enqueue and dequeue states of a queue by adjusting timestamps and transferring queuing state information between nodes, ensuring that the migrated session experiences the same behavior as the original session, using techniques like Advanced Queuing and flashback query features to maintain the proper order and sequence of messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If session migration is implemented in multi-node database systems, then session continuity and system availability are improved, but queue state consistency deteriorates because existing techniques fail to preserve queuing state information during migration
Solution Approach 1:
The patent applies preliminary action by capturing the queue state information (enqueue state and dequeue state) before session migration occurs. The system stores the state of the queue at the time of migration in a manner that allows reconstruction after migration, ensuring that the migrated session can resume queue operations with the correct state rather than starting from scratch or losing state information.
Solution Approach 2:
The patent uses copying by creating a representation of the queue state that can be transferred between nodes. The enqueue state and dequeue state are captured and reconstructed on the target node, effectively copying the essential state information needed to maintain queue behavior consistency across node migration.
2Stability of the object's composition
If queue state information is transferred during session migration, then message ordering and sequence consistency are improved, but system complexity increases due to the need to capture and reconstruct enqueue and dequeue states
Solution Approach 1:
The patent applies segmentation by dividing the queue state into distinct components: enqueue state information and dequeue state information. This segmentation allows the system to handle each aspect of queue state separately, making the migration process more manageable and the reconstruction logic more straightforward despite the overall system complexity.
3Stability of the object's composition
If timestamp adjustment is used to maintain queue state during migration, then message ordering is preserved, but processing time increases due to the overhead of capturing and adjusting timestamps
Solution Approach 1:
The patent applies parameter changes by adjusting timestamps as part of the queue state capture and reconstruction process. The system modifies timestamp parameters to reflect the correct temporal ordering of messages in the migrated session, ensuring that message ordering is preserved even when the session moves between nodes with different system clocks.
Data Source
AI summary
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.