Database Log Replay for Transaction Consistency in Disaster Recovery
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Solution Overview
Problem
Conventional disaster recovery systems face challenges in ensuring data consistency at the transaction level during disasters, leading to inefficiencies in data recovery and business continuity, particularly due to the Rolling Disaster scenario where system elements fail at different times, and existing solutions require complex processes to maintain consistency.
Innovation Solution
A data duplication method that records and transfers log updates from a primary database to a secondary database, including operation commands, to ensure transaction-level consistency, allowing for seamless recovery and operation without data deficits, using a process that includes snapshot preparation and mirror set management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is backed up to secondary site during Rolling Disaster, then data redundancy is improved, but data consistency at transaction level deteriorates
Solution Approach 1:
The system performs preliminary actions by recording operation commands (not just data changes) in the log before transactions are committed. This allows the secondary site to replay commands in the correct sequence, ensuring transaction-level consistency even during Rolling Disaster scenarios where the primary site may fail mid-transaction.
Solution Approach 2:
The log acts as an intermediary between the primary and secondary databases. Instead of directly copying data states which may be inconsistent during disasters, the log transmits a complete record of operations that can be replayed to reconstruct the database state, ensuring consistency across sites.
2Manufacturing precision
If complex processes are used to maintain data consistency, then data consistency is improved, but system complexity deteriorates
Solution Approach 1:
The system copies the complete log (including operation commands) from the primary to the secondary site. This simple copy operation, combined with command replay, achieves transaction-level consistency without requiring complex coordination protocols or multiple synchronization steps between sites.
Solution Approach 2:
The system changes the parameter being transmitted from mere data values to data values plus operation commands. This parameter enhancement in the log allows the secondary site to reconstruct transactions accurately, simplifying the consistency maintenance process while improving data consistency.
3Manufacturing precision
If log includes operation commands, then data consistency is improved, but data transfer volume deteriorates
Solution Approach 1:
The system extracts only the essential operation commands from the log that are necessary for replaying transactions at the secondary site. By taking out only the critical command information rather than transmitting redundant data, the system maintains data consistency while minimizing data transfer volume.
4Productivity
If secondary site performs searching process, then productivity is improved, but data consistency deteriorates
Solution Approach 1:
The secondary site performs searching operations on data that has been preliminarily prepared through log replay. This allows the secondary site to provide productivity benefits (searching capability) while maintaining data consistency, because the search operations work on data that has been correctly reconstructed from the log commands.
Data Source
AI summary
A recovery of a secondary DB is executed by a log including a update difference of a primary DB, and a command is executed by adding the command to the log and analyzing the log by a secondary site. An operation command execution in the secondary site is applied to the DB having the consistency in the transaction at the same timing as a primary site or an intended timing, by transferring and executing the operation command via the log. In the case that the command is constituted by a snap shot generating instruction, a plurality of volumes of a mirror set forming a secondary storage apparatus are set to a pair state and the secondary DB is written in each of the volumes and synchronized, and the mirror set is set to a split state after the synchronization is finished, whereby a secondary DB is stored.