Global Checkpoint SCN for Multi-Node Data Consistency
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Solution Overview
Problem
In multi-node systems, the overhead associated with acquiring and managing global locks for accessing shared resources is significant due to bandwidth, time, and computational complexity, leading to substantial delays in data access.
Innovation Solution
The implementation of a global checkpoint system change number (SCN) allows for the computation of snapshot queries without the need for global locks when the snapshot time is prior to the global checkpoint SCN, thereby reducing the complexity and overhead of lock management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If global locks are used to synchronize access to shared resources in multi-node systems, then data consistency and reliability are improved, but bandwidth consumption, time delay, and computational complexity increase significantly
Solution Approach 1:
The patent segments the global lock management into local checkpoint SCN maintenance at each node and global SCN generation only when needed. Each node independently maintains its local checkpoint SCN, eliminating the need for continuous global lock coordination and reducing overall system complexity while maintaining data consistency.
Solution Approach 2:
The patent performs preliminary action by pre-generating and storing checkpoint SCNs at each node before they are needed for snapshot queries. This allows nodes to have the necessary synchronization information readily available without requiring real-time global lock acquisition, thereby reducing time delay and bandwidth consumption.
2Measurement precision
If global locks are acquired for snapshot queries, then data accuracy is improved, but time delay and bandwidth consumption increase
Solution Approach 1:
The patent introduces the global checkpoint SCN as an intermediary that mediates between multiple nodes for snapshot queries. Instead of requiring direct global lock acquisition between nodes, the global checkpoint SCN serves as a shared reference point that all nodes can use independently to ensure snapshot data accuracy without the overhead of inter-node lock coordination.
Solution Approach 2:
The patent uses copying by distributing the global checkpoint SCN to all nodes. Each node maintains a copy of the global checkpoint SCN locally, allowing them to perform accurate snapshot queries using their local copy without needing to communicate with other nodes or acquire global locks, thereby reducing query execution time and bandwidth consumption.
3Loss of information
If global locks are used to check for stale data blocks, then data freshness is improved, but computational complexity and time delay increase
Solution Approach 1:
The patent implements self-service by enabling each node to independently determine data freshness using its local checkpoint SCN and the global checkpoint SCN. Nodes can autonomously check whether their data blocks are stale by comparing SCNs without requiring global lock acquisition or communication with other nodes, thereby maintaining data freshness information while significantly improving data access efficiency.
Data Source
AI summary
Described herein are techniques for generating a global checkpoint system change number and computing a snapshot query using the global checkpoint system change number without a need to acquire global locks. In many cases, the need to acquire global locks is eliminated, thereby saving the overhead attendant to processing global locks.