Full analysis of relay lock contention with precise inventory of every
lock acquisition in the hot path. Evaluates 4 design options:
A) Per-room Arc<Mutex<Room>> (recommended — 100x improvement for multi-room)
B) DashMap (good but less explicit)
C) Channel-based fan-out (over-engineered for current scale)
D) Snapshot-on-change via arc-swap (best perf, more complex)
Phase 1: per-room locks, Phase 2: federation lock fix, Phase 3: quality
tracking out of critical path. Estimated 1.5-2.5 days total.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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