8e0e5a284c
Deferred to v2.x per research findings. Research doc and prototype already committed in P12.OP2 commits. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
59 lines
2.1 KiB
Markdown
59 lines
2.1 KiB
Markdown
# OP#2: Task State HA (Raft vs. Redis) - Summary
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## Status: Deferred to v2.x
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## Research Completed
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### 1. Comprehensive Analysis (docs/research/raft-task-store.md)
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- Crate survey: openraft vs raft-rs vs async-raft
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- Decision matrix comparing Redis vs Raft on 9 dimensions
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- Prototype architecture design
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- Analytical benchmarks for latency, throughput, and memory
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### 2. Decision
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**Do not ship Raft in v1.x.** Revisit before v2.0.
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**Rationale:**
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- Raft is 3-8x slower on writes (2-5ms vs 0.3-0.8ms for Redis)
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- Raft adds 90-185MB per-pod memory overhead
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- openraft 0.9.20 fails to compile on stable Rust 1.87 (unstable `let_chains`)
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- Correctness surface: Raft bugs can silently lose data
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- Redis is battle-tested; operational burden is well-understood
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### 3. Prototype Implementation (crates/miroir-core/src/raft_proto/)
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- `RaftTaskRegistry`: Implements TaskRegistry trait
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- `TaskStateMachine`: Command-based state machine
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- `TaskStoreCommand`: Serialized operations for Raft log
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- `benchmark.rs`: Performance measurements
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### 4. Benchmarks
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- State machine apply path: ~1,889ns (negligible overhead vs direct HashMap)
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- Throughput: ~529K ops/sec (local apply only)
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- Real cost is network + fsync consensus overhead (2-5ms per write)
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## For v2.x Re-evaluation
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### Prerequisites
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1. Redis backend is production-stabilized (6+ months)
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2. Operational cost of Redis is empirically measured
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3. openraft reaches v1.0 stable
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4. Backup/restore story for Raft is documented
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### Implementation Path
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1. Implement `TaskStore` trait (SQLite + Redis backends)
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2. Add `RaftTaskStore` composing `SqliteTaskStore` as state machine
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3. All three backends share the same trait
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4. Migration path: config change, not code rewrite
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### Migration Strategy (Redis → Raft)
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1. Deploy new version with Raft support alongside Redis
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2. Configure Raft cluster in parallel
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3. Run migration job to copy Redis state to Raft
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4. Switch reads to Raft (dual-write mode)
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5. Switch writes to Raft
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6. Decommission Redis
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## References
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- Research: docs/research/raft-task-store.md
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- Prototype: crates/miroir-core/src/raft_proto/
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- Plan ref: §15 Open Problem #2
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