guyinyou opened a new issue, #9735: URL: https://github.com/apache/rocketmq/issues/9735
### Before Creating the Enhancement Request - [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature. ### Summary Add a snapshot backup and recovery mechanism for TimerWheel to ensure reliable recovery of timer message state after broker restarts. Currently, the discrete TimerWheel state cannot be fully recovered from TimerLog alone, leading to potential data inconsistency and performance issues during recovery. ### Motivation The current implementation has a critical limitation where TimerWheel state is not persisted, making it impossible to fully recover the timer message scheduling state after a broker restart. This creates several problems: Data Recovery Issues: TimerWheel contains crucial scheduling information that cannot be reconstructed from TimerLog alone Performance Impact: During recovery, the entire TimerWheel needs to be rebuilt from scratch, which is time-consuming and resource-intensive Data Consistency: Without proper state recovery, some timer messages may be lost or incorrectly scheduled Operational Reliability: Production environments require reliable recovery mechanisms to ensure business continuity This enhancement is particularly important for: High-availability deployments where broker restarts are common Large-scale timer message processing scenarios Production environments requiring consistent timer message delivery ### Describe the Solution You'd Like Implement a comprehensive snapshot mechanism for TimerWheel with the following components: 1. Configuration Options timerWheelSnapshotFlush: Enable/disable snapshot functionality (default: false for backward compatibility) timerWheelDefaultFlush: Control default flush behavior (default: true) timerWheelSnapshotIntervalMs: Configure snapshot creation interval (default: 10 seconds) 2. Snapshot Management Snapshot Creation: Periodically backup TimerWheel state to snapshot files Snapshot Recovery: Support recovery from the latest snapshot file during initialization Snapshot Cleanup: Automatically clean up expired snapshot files to manage disk space Atomic Operations: Ensure snapshot operations are atomic to prevent corruption 3. Implementation Details Add backup() method to TimerWheel for creating snapshots Modify TimerWheel constructor to support recovery from snapshots Implement snapshot file selection logic based on flush positions Add synchronization locks to ensure flush operations are atomic Integrate snapshot functionality into TimerFlushService 4. Backward Compatibility Default configuration maintains existing behavior Existing deployments continue to work without changes Gradual migration path for enabling snapshot functionality ### Describe Alternatives You've Considered Alternative 1: Enhanced TimerLog Recovery Approach: Improve TimerLog to include all necessary TimerWheel state information Why Rejected: This would require significant changes to the existing TimerLog format and could break backward compatibility. It would also increase the complexity of the logging mechanism. Alternative 2: In-Memory State Persistence Approach: Persist TimerWheel state to a separate state file during normal operations Why Rejected: This approach would require frequent disk I/O operations during normal message processing, which could significantly impact performance. Alternative 3: Database-Based State Storage Approach: Store TimerWheel state in an external database Why Rejected: This would introduce external dependencies and complexity, making the system harder to deploy and maintain. It would also add network latency and potential failure points. Alternative 4: Checkpoint-Based Recovery Approach: Use existing checkpoint mechanism to store TimerWheel state Why Rejected: The current checkpoint mechanism is not designed for complex data structures like TimerWheel, and modifying it would affect other parts of the system. The proposed snapshot mechanism provides the best balance of: Performance: Minimal impact on normal operations Reliability: Atomic operations ensure data consistency Compatibility: Backward compatible with existing deployments Simplicity: Clean separation of concerns without affecting existing code paths ### Additional Context _No response_ -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
