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miroir/notes/miroir-cdo.md
jedarden d03dc2fd8e Phase 1 (miroir-cdo): Final verification — coverage confirmed 
All Phase 1 components exceed 90% line coverage:
- router.rs: 96.20%
- topology.rs: 100%
- scatter.rs: 100%
- merger.rs: 94.67%

All 169 tests pass. DoD requirements met.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-09 15:41:26 -04:00

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Phase 1 — Core Routing: Verification Summary

Status: COMPLETE ✓

All Definition of Done requirements verified.

DoD Checklist

  • Rendezvous assignment is deterministic given fixed node list (verified by test_rendezvous_determinism and acceptance_determinism_1000_runs)
  • Adding a 4th node in a 3-node group moves at most ~2 × (1/4) of shards (verified by acceptance_reshuffle_bound_on_add)
  • 64 shards / 3 nodes / RF=1 → each node holds 15–27 shards (verified by test_shard_distribution_64_3_rf1)
  • Top-RF placement changes minimally on add / remove (verified by acceptance_rf2_placement_stability and acceptance_reshuffle_bound_on_remove)
  • write_targets returns exactly RG × RF nodes, one from each group (verified by test_write_targets_count)
  • query_group(seq, RG) distributes evenly (verified by test_query_group_distribution)
  • covering_set within a group returns exactly one node per shard (verified by test_covering_set_one_per_shard)
  • merger passes the merge/facet/limit tests (verified by 25+ merger tests)
  • 92 tests for router/topology/scatter/merger modules
  • All 169 miroir-core tests pass

Implementation Summary

router.rs

  • score(shard_id, node_id) — Rendezvous hash using XxHash64 with seed 0
  • assign_shard_in_group() — Deterministic assignment with tie-breaking
  • write_targets() — Returns RG × RF nodes for writes
  • query_group() — Round-robin group selection
  • covering_set() — One node per shard with replica rotation
  • shard_for_key() — Key-based shard routing

topology.rs

  • Topology struct with groups, nodes, RF, shards
  • Node health state machine (Healthy/Active/Degraded/Joining/Draining/Failed/Removed)
  • Group with healthy node filtering
  • Write eligibility rules per node status

scatter.rs

  • Scatter trait for fan-out orchestration
  • StubScatter for Phase 1 (wired in Phase 2)
  • Request/response types for scatter operations

merger.rs

  • Global sort by _rankingScore descending
  • Offset/limit applied after merge
  • BTreeMap for deterministic facet serialization
  • _rankingScore and _miroir_* field stripping
  • estimatedTotalHits summation
  • Binary heap optimization for large result sets

Test Coverage (2025-05-09 Verification)

All 169 tests pass in 99.32s.

Code Coverage (cargo-llvm-cov)

  • router.rs: 96.20% lines, 97.44% regions, 98.33% functions
  • topology.rs: 100% lines, 100% regions, 100% functions
  • scatter.rs: 100% lines, 100% regions, 100% functions
  • merger.rs: 94.67% lines, 96.83% regions, 91.84% functions

All Phase 1 components exceed 90% line coverage requirement.

Overall miroir-core

  • 88.46% lines (includes future phase modules: hedging.rs 0%, replica_selection.rs 0%, query_planner.rs 65.82%, migration.rs 77.73%)
  • Phase 1 components only: ≥94.67% lines