400caa5483
Verify that the three core rendezvous hash primitives (score, assign_shard_in_group, shard_for_key) are correctly implemented in miroir_core::router. All implementations match the specification: - score: Uses XxHash64::with_seed(0) with canonical (shard_id, node_id) order - assign_shard_in_group: Group-scoped assignment with score sort and lexicographic tie-breaking - shard_for_key: Uses XxHash64::with_seed(0) to hash primary_key All 26 acceptance tests pass: - Determinism across 1000 runs - Reshuffle bounds on add/remove - Uniformity distribution (15-27 shards per node) - RF=2 placement stability - shard_for_key fixture verification Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
49 lines
2 KiB
Markdown
49 lines
2 KiB
Markdown
# P1.1 Rendezvous Hash Primitives - Verification Complete
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## Task Status
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**COMPLETE** - All three required functions were already implemented in `/home/coding/miroir/crates/miroir-core/src/router.rs`
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## Implementations Verified
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### 1. `score(shard_id: u32, node_id: &str) -> u64`
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- Uses `XxHash64::with_seed(0)` (line 15)
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- Canonical concatenation order: `(shard_id, node_id)` (lines 16-17)
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- Returns `u64` hash value (line 18)
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### 2. `assign_shard_in_group(shard_id: u32, group_nodes: &[NodeId], rf: usize) -> Vec<NodeId>`
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- Computes score for each node in the group (line 30)
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- Sorts by score descending (line 33)
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- Breaks ties lexicographically on node_id (line 34)
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- Returns top `rf` nodes (lines 37-40)
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### 3. `shard_for_key(primary_key: &str, shard_count: u32) -> u32`
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- Uses `XxHash64::with_seed(0)` (line 73)
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- Hashes primary_key (line 74)
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- Returns `hash % shard_count` as u32 (line 75)
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## Acceptance Tests (All Passed ✓)
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1. **Determinism** - 1000 randomized runs all produce identical assignments
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2. **Reshuffle bound on add** - 64 shards, 3→4 nodes: ≤ 32 edges differ
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3. **Reshuffle bound on remove** - 64 shards, 4→3 nodes: ~32 edges differ
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4. **Uniformity** - 64 shards, 3 nodes, RF=1: each node holds 15-27 shards
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5. **RF=2 placement stability** - Top-2 nodes change minimally on add/remove
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6. **shard_for_key fixture** - Verified against known test vectors
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7. **Tie-breaking** - Lexicographic on node_id for identical scores
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8. **Canonical order** - (shard_id, node_id) produces different hash than (node_id, shard_id)
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## Test Results
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```
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running 26 tests
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test result: ok. 26 passed; 0 failed; 0 ignored
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```
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## Key Design Constraints Verified
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- Hash function: `twox-hash` (XxHash family) ✓
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- Seed: 0 (matches Meilisearch Enterprise) ✓
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- Concatenation order: (shard_id, node_id) ✓
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- Group-scoped assignment: prevents same-group replicas ✓
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- Tie-breaking: lexicographic on node_id ✓
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## Files Modified
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None - implementations were already correct and complete.
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