miroir/notes/miroir-cdo-phase1-final-verification.md
jedarden f513bf096c Phase 1 (miroir-cdo): Core Routing — Final verification summary
All definition of done criteria verified:
- Router correctness: 26/26 tests pass
- Merger functionality: 22/22 tests pass
- Topology health state machine: 45/45 tests pass
- Coverage: 91.80% (exceeds 90% requirement)

Key results:
- Rendezvous assignment is deterministic (verified across 1000 runs)
- Minimal reshuffling on node add/remove (HRW property verified)
- Uniform distribution: 64 shards / 3 nodes → 15-27 shards per node
- write_targets returns exactly RG × RF nodes
- covering_set returns one node per shard with replica rotation
- Merger handles global sort, offset/limit, facets, degraded mode

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-09 12:03:18 -04:00

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# Phase 1 (miroir-cdo): Core Routing — Final Verification Summary
**Date**: 2026-05-09
**Session**: Final verification of Phase 1 Core Routing implementation
## Definition of Done Checklist
### ✅ Router Correctness (plan §8)
1. **Rendezvous assignment determinism**: ✅ PASSED
- `test_rendezvous_determinism`: Same (shard_id, nodes) → identical Vec<NodeId>
- `acceptance_determinism_1000_runs`: 1000 randomized runs, all deterministic
2. **Minimal reshuffling on node add**: ✅ PASSED
- `test_minimal_reshuffling_on_add`: Adding 4th node moves ≤ 50% of shards
- `acceptance_reshuffle_bound_on_add`: 64 shards, 3→4 nodes → ≤ 32 edges differ
3. **Uniform shard distribution**: ✅ PASSED
- `test_shard_distribution_64_3_rf1`: 64 shards / 3 nodes / RF=1 → 15-27 shards per node
- `acceptance_uniformity_64_shards_3_nodes_rf1`: Each node holds 15-27 shards
4. **Top-RF placement stability**: ✅ PASSED
- `test_top_rf_stability`: Top-RF nodes change minimally on add/remove
- `acceptance_rf2_placement_stability`: RF=2 placement stable on node change
- `acceptance_reshuffle_bound_on_remove`: 4→3 nodes, ~RF × S / Ng edges differ
5. **write_targets returns RG × RF nodes**: ✅ PASSED
- `test_write_targets_count`: Exactly RG × RF nodes returned
- `test_group_scoped_assignment`: One node from each replica group
6. **query_group distributes evenly**: ✅ PASSED
- `test_query_group_distribution`: Round-robin distribution verified
7. **covering_set returns one node per shard**: ✅ PASSED
- `test_covering_set_one_per_shard`: Exactly one node per shard
- `test_covering_set_replica_rotation`: Intra-group replica rotation works
### ✅ Result Merger (plan §8)
1. **Global sort by _rankingScore**: ✅ PASSED
- `test_global_sort_by_ranking_score`: Descending order verified
2. **Offset/limit after merge**: ✅ PASSED
- `test_offset_and_limit_applied_after_merge`: Pagination works correctly
3. **_rankingScore stripping**: ✅ PASSED
- `test_ranking_score_stripped_when_not_requested`: Strips when not requested
- `test_ranking_score_included_when_requested`: Includes when requested
4. **_miroir_shard stripping**: ✅ PASSED
- `test_miroir_shard_always_stripped`: Always stripped
- `test_strip_all_miroir_reserved_fields`: All _miroir_* fields stripped
5. **Facet aggregation**: ✅ PASSED
- `test_facet_counts_summed_across_shards`: Sums counts across shards
- `test_facet_filter_only_merges_requested_facets`: Filter works
6. **estimatedTotalHits summation**: ✅ PASSED
- `test_estimated_total_hits_summed`: Correctly summed
7. **processingTimeMs max**: ✅ PASSED
- `test_processing_time_max_across_shards`: Max taken correctly
8. **Tie-breaking**: ✅ PASSED
- `test_tie_breaking_by_primary_key`: Primary key ascending for ties
9. **Degraded mode**: ✅ PASSED
- `test_degraded_flag_when_shard_fails`: Flag set when shards fail
- `test_not_degraded_when_all_succeed`: Flag not set when all succeed
10. **Stable serialization**: ✅ PASSED
- `test_stable_serialization_same_input_same_json`: BTreeMap ensures deterministic JSON
### ✅ Topology (plan §2)
- `topology.rs`: 100.00% line coverage
- All state transitions tested
- Write eligibility rules tested
- Group isolation tested
### ✅ Scatter (plan §2)
- `scatter.rs`: 100.00% line coverage
- Stub implementation for Phase 2 wiring
## Coverage Report (2026-05-09)
```
Filename Regions Missed Regions Cover Functions Missed Functions Executed Lines Missed Lines Cover Branches Missed Branches Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
anti_entropy.rs 56 0 100.00% 7 0 100.00% 70 0 100.00% 0 0 -
config.rs 293 26 91.13% 30 5 83.33% 306 18 94.12% 0 0 -
config/advanced.rs 166 16 90.36% 32 2 93.75% 288 20 93.06% 0 0 -
config/load.rs 159 77 51.57% 9 2 77.78% 140 28 80.00% 0 0 -
config/validate.rs 86 27 68.60% 1 0 100.00% 108 46 57.41% 0 0 -
merger.rs 977 31 96.83% 49 4 91.84% 582 31 94.67% 0 0 -
migration.rs 721 163 77.39% 43 12 72.09% 467 104 77.73% 0 0 -
reshard.rs 455 47 89.67% 36 7 80.56% 324 34 89.51% 0 0 -
router.rs 1016 26 97.44% 60 1 98.33% 500 19 96.20% 0 0 -
scatter.rs 214 0 100.00% 11 0 100.00% 121 0 100.00% 0 0 -
score_comparability.rs 589 10 98.30% 32 0 100.00% 325 9 97.23% 0 0 -
task.rs 164 0 100.00% 16 0 100.00% 118 0 100.00% 0 0 -
topology.rs 776 0 100.00% 70 0 100.00% 421 0 100.00% 0 0 -
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL 5672 423 92.54% 396 33 91.67% 3770 309 91.80% 0 0 -
```
**Overall `miroir-core` line coverage: 91.80%** (exceeds 90% requirement)
## Test Results
**Total tests run**: 151
**Passed**: 151
**Failed**: 0
**Ignored**: 0
### Breakdown by module:
- **router.rs**: 26 tests passed
- **topology.rs**: 45 tests passed
- **merger.rs**: 22 tests passed
- **scatter.rs**: 6 tests passed
## Key Implementation Details
### Rendezvous Hashing (HRW)
- Uses `twox_hash::XxHash64` with seed 0 (matches Meilisearch Enterprise)
- Canonical order: `(shard_id, node_id)` - critical for determinism
- Tie-breaking: lexicographic by `node_id` for identical scores
### Group Isolation
- Hashing scoped to intra-group node lists
- Prevents both replicas of a shard from landing in the same group
- `write_targets()` returns exactly `RG × RF` nodes, one from each group
### Minimal Reshuffling
- Adding a node to a group moves ~1/(Ng+1) of that group's docs
- Top-RF placement changes minimally on add/remove
### Result Merger
- Uses binary min-heap for efficient top-k selection
- BTreeMap for stable facet serialization
- Always strips `_miroir_*` reserved fields
- Conditionally strips `_rankingScore` based on client request
## Status: COMPLETE ✅
All Phase 1 Core Routing requirements have been implemented and verified.
The foundation is ready for Phase 2 (write path) and Phase 3 (read path).