seaweedfs/SMQ_OFFSET_DEVELOPMENT_PLAN.md

SMQ Native Offset Development Plan

Overview

Add native per-partition sequential offsets to SeaweedMQ to eliminate the need for external offset mapping and provide better interoperability with message queue protocols.

Architecture Changes

Data Model

• Add offset field (int64) to each record alongside existing ts_ns
• Offset domain: per schema_pb.Partition (ring range)
• Offsets are strictly monotonic within a partition
• Leader assigns offsets; followers replicate

Storage

• Use _index as hidden SQL table column for offset storage
• Maintain per-partition offset counters in broker state
• Checkpoint offset state periodically for recovery

Development Phases

Phase 1: Proto and Data Model Changes

Scope: Update protobuf definitions and core data structures

Tasks:

1. Update mq_schema.proto:
   • Add offset field to record storage format
   • Add offset-based OffsetType enums
   • Add offset_value field to subscription requests
2. Update mq_agent.proto:
   • Add base_offset and last_offset to PublishRecordResponse
   • Add offset field to SubscribeRecordResponse
3. Regenerate protobuf Go code
4. Update core data structures in broker code
5. Add offset field to SQL schema with _index column

Tests:

• Proto compilation tests
• Data structure serialization tests
• SQL schema migration tests

Deliverables:

• Updated proto files
• Generated Go code
• Updated SQL schema
• Basic unit tests

Phase 2: Offset Assignment Logic

Scope: Implement offset assignment in broker

Tasks:

1. Add PartitionOffsetManager component:
   • Track next_offset per partition
   • Assign sequential offsets to records
   • Handle offset recovery on startup
2. Integrate with existing record publishing flow:
   • Assign offsets before storage
   • Update PublishRecordResponse with offset info
3. Add offset persistence to storage layer:
   • Store offset alongside record data
   • Index by offset for efficient lookups
4. Implement offset recovery:
   • Load highest offset on partition leadership
   • Handle clean and unclean restarts

Tests:

• Offset assignment unit tests
• Offset persistence tests
• Recovery scenario tests
• Concurrent assignment tests

Deliverables:

• PartitionOffsetManager implementation
• Integrated publishing with offsets
• Offset recovery logic
• Comprehensive test suite

Phase 3: Subscription by Offset

Scope: Enable consumers to subscribe using offsets

Tasks:

1. Extend subscription logic:
   • Support EXACT_OFFSET and RESET_TO_OFFSET modes
   • Add offset-based seeking
   • Maintain backward compatibility with timestamp-based seeks
2. Update SubscribeRecordResponse:
   • Include offset in response messages
   • Ensure offset ordering in delivery
3. Add offset validation:
   • Validate requested offsets are within valid range
   • Handle out-of-range offset requests gracefully
4. Implement offset-based filtering and pagination

Tests:

• Offset-based subscription tests
• Seek functionality tests
• Out-of-range offset handling tests
• Mixed timestamp/offset subscription tests

Deliverables:

• Offset-based subscription implementation
• Updated subscription APIs
• Validation and error handling
• Integration tests

Phase 4: High Water Mark and Lag Calculation

Scope: Implement native offset-based metrics

Tasks:

1. Add high water mark tracking:
   • Track highest committed offset per partition
   • Expose via broker APIs
   • Update on successful replication
2. Implement lag calculation:
   • Consumer lag = high_water_mark - consumer_offset
   • Partition lag metrics
   • Consumer group lag aggregation
3. Add offset-based monitoring:
   • Partition offset metrics
   • Consumer position tracking
   • Lag alerting capabilities
4. Update existing monitoring integration

Tests:

• High water mark calculation tests
• Lag computation tests
• Monitoring integration tests
• Metrics accuracy tests

Deliverables:

• High water mark implementation
• Lag calculation logic
• Monitoring integration
• Metrics and alerting

Phase 5: Kafka Gateway Integration

Scope: Update Kafka gateway to use native SMQ offsets

Tasks:

1. Remove offset mapping layer:
   • Delete kafka-system/offset-mappings topic usage
   • Remove PersistentLedger and SeaweedMQStorage
   • Simplify offset translation logic
2. Update Kafka protocol handlers:
   • Use native SMQ offsets in Produce responses
   • Map SMQ offsets directly to Kafka offsets
   • Update ListOffsets and Fetch handlers
3. Simplify consumer group offset management:
   • Store Kafka consumer offsets as SMQ offsets
   • Remove timestamp-based offset translation
4. Update integration tests:
   • Test Kafka client compatibility
   • Verify offset consistency
   • Test long-term disconnection scenarios

Tests:

• Kafka protocol compatibility tests
• End-to-end integration tests
• Performance comparison tests
• Migration scenario tests

Deliverables:

• Simplified Kafka gateway
• Removed offset mapping complexity
• Updated integration tests
• Performance improvements

Phase 6: Performance Optimization and Production Readiness

Scope: Optimize performance and prepare for production

Tasks:

1. Optimize offset assignment performance:
   • Batch offset assignment
   • Reduce lock contention
   • Optimize recovery performance
2. Add offset compaction and cleanup:
   • Implement offset-based log compaction
   • Add retention policies based on offsets
   • Cleanup old offset checkpoints
3. Enhance monitoring and observability:
   • Detailed offset metrics
   • Performance dashboards
   • Alerting on offset anomalies
4. Load testing and benchmarking:
   • Compare performance with timestamp-only approach
   • Test under high load scenarios
   • Validate memory usage patterns

Tests:

• Performance benchmarks
• Load testing scenarios
• Memory usage tests
• Stress testing under failures

Deliverables:

• Optimized offset implementation
• Production monitoring
• Performance benchmarks
• Production deployment guide

Implementation Guidelines

Code Organization

weed/mq/
├── offset/
│   ├── manager.go          # PartitionOffsetManager
│   ├── recovery.go         # Offset recovery logic
│   └── checkpoint.go       # Offset checkpointing
├── broker/
│   ├── partition_leader.go # Updated with offset assignment
│   └── subscriber.go       # Updated with offset support
└── storage/
    └── offset_store.go     # Offset persistence layer

Testing Strategy

• Unit tests for each component
• Integration tests for cross-component interactions
• Performance tests for offset assignment and recovery
• Compatibility tests with existing SMQ features
• End-to-end tests with Kafka gateway

Commit Strategy

• One commit per completed task within a phase
• All tests must pass before commit
• No binary files in commits
• Clear commit messages describing changes

Rollout Plan

1. Deploy to development environment after Phase 2
2. Integration testing after Phase 3
3. Performance testing after Phase 4
4. Kafka gateway migration after Phase 5
5. Production rollout after Phase 6

Success Criteria

Phase Completion Criteria

• All tests pass
• Code review completed
• Documentation updated
• Performance benchmarks meet targets

Overall Success Metrics

• Eliminate external offset mapping complexity
• Maintain or improve performance
• Full Kafka protocol compatibility
• Native SMQ offset support for all protocols
• Simplified consumer group offset management

Risk Mitigation

Technical Risks

• Offset assignment bottlenecks: Implement batching and optimize locking
• Recovery performance: Use checkpointing and incremental recovery
• Storage overhead: Optimize offset storage and indexing

Operational Risks

• Migration complexity: Implement gradual rollout with rollback capability
• Data consistency: Extensive testing of offset assignment and recovery
• Performance regression: Continuous benchmarking and monitoring

Timeline Estimate

• Phase 1: 1-2 weeks
• Phase 2: 2-3 weeks
• Phase 3: 2-3 weeks
• Phase 4: 1-2 weeks
• Phase 5: 2-3 weeks
• Phase 6: 2-3 weeks

Total: 10-16 weeks

Implementation Status

• Phase 1: Protocol Schema Updates ✅

  • Updated mq_schema.proto with offset fields and offset-based OffsetType enums
  • Updated mq_agent.proto with offset fields in publish/subscribe responses
  • Regenerated protobuf Go code
  • Added comprehensive proto serialization tests
  • All tests pass, ready for Phase 2

• Phase 2: Offset Assignment Logic ✅

  • Implemented PartitionOffsetManager for sequential offset assignment per partition
  • Added OffsetStorage interface with in-memory and SQL storage backends
  • Created PartitionOffsetRegistry for managing multiple partition offset managers
  • Implemented robust offset recovery from checkpoints and storage scanning
  • Added comprehensive tests covering assignment, recovery, and concurrency
  • All tests pass, thread-safe and recoverable offset assignment complete

• Phase 3: Subscription by Offset ✅

  • Implemented OffsetSubscriber for managing offset-based subscriptions
  • Added OffsetSubscription with seeking, lag tracking, and range operations
  • Created OffsetSeeker for offset validation and range utilities
  • Built SMQOffsetIntegration for bridging offset management with SMQ broker
  • Support for all OffsetType variants and comprehensive error handling
  • Added extensive test coverage (40+ tests) for all subscription scenarios
  • All tests pass, providing robust offset-based messaging foundation

• Phase 4: Broker Integration

• Phase 5: SQL Storage Backend

• Phase 6: Testing and Validation

Next Steps

1. Review and approve development plan ✅
2. Set up development branch ✅
3. Begin Phase 1 implementation ✅
4. Continue with Phase 4: Broker Integration
5. Establish testing and CI pipeline
6. Regular progress reviews and adjustments