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miroir/notes/miroir-mkk.2.md
jedarden 6b52d22771 P4.2: Verify node addition with dual-write + paginated migration 
Verified the P4.2 implementation is complete:
- All 6 integration tests pass (p42_node_addition.rs)
- All 14 cutover chaos tests pass
- All 8 topology chaos tests pass
- Core components: rebalancer.rs, migration.rs, rebalancer_worker/mod.rs
- Admin API: POST /_miroir/nodes endpoint

Acceptance criteria met:
- 3→4 node migration with 10K docs verified
- Chaos testing confirms dual-write catches late writes
- Performance bounds verified (≤total_docs/(Ng+1)×1.1)
- Log inspection confirms old node not queried after migration

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-23 08:21:00 -04:00

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P4.2 Node Addition: Dual-Write + Paginated Shard Migration - Verification

Summary

Verified that the P4.2 node addition implementation is complete and fully functional. All acceptance criteria tests pass.

Implementation Verified

Core Components (Already Implemented)

  1. crates/miroir-core/src/rebalancer.rs:

    • add_node() method creates node addition operation
    • compute_shard_moves_for_new_node() determines affected shards
    • run_migration_task() executes paginated migration with dual-write
    • HttpMigrationExecutor implements actual HTTP-based document migration
    • Delta pass support for catching stragglers

  2. crates/miroir-core/src/migration.rs:

    • Complete migration state machine with all phases
    • MigrationCoordinator for state transitions
    • begin_dual_write() starts dual-write phase
    • begin_cutover(), complete_drain(), complete_cleanup() for cutover sequence
    • Safety validation (anti-entropy required if delta pass skipped)

  3. crates/miroir-core/src/rebalancer_worker/mod.rs:

    • Background worker with leader lease
    • on_node_added() handles topology events
    • drive_migrations() advances migration state machine
    • Job persistence via TaskStore

  4. crates/miroir-proxy/src/routes/admin_endpoints.rs:

    • add_node API endpoint
    • Integration with rebalancer worker via event channel

Integration Tests (All Pass)

crates/miroir-core/tests/p42_node_addition.rs:

  1. p42_node_addition_3_to_4_migration_10k_docs - 10K docs migration test
  2. p42_chaos_writes_during_migration_dual_write - Dual-write chaos test
  3. p42_performance_document_count_bounds - Performance bounds verification
  4. p42_log_inspection_old_node_not_queried_after_migration - Log inspection test
  5. p42_verify_dual_write_during_migration - Dual-write verification
  6. p42_pagination_limit_offset - Pagination verification

crates/miroir-core/tests/cutover_race.rs:

  • 14 chaos tests for cutover boundary conditions
  • All pass with anti-entropy and delta pass

crates/miroir-core/tests/p4_topology_chaos.rs:

  • 8 topology chaos tests
  • All pass

Acceptance Criteria Status

  • Integration test: 3-node → 4-node migration, 10K docs, each doc still retrievable by ID after migration
  • Chaos: toggle writes on/off during migration; dual-write window catches all late writes
  • Performance: migrating ~S/(Ng+1) shards moves ≤ total_docs / (Ng+1) × 1.1 docs (10% slack for dual-write dupes)
  • The old node is not queried for the migrated shards after step 8 (verified via log inspection)

Test Results

running 6 tests (p42_node_addition)
test p42_chaos_writes_during_migration_dual_write ... ok
test p42_node_addition_3_to_4_migration_10k_docs ... ok
test p42_log_inspection_old_node_not_queried_after_migration ... ok
test p42_performance_document_count_bounds ... ok
test p42_verify_dual_write_during_migration ... ok
test p42_pagination_limit_offset ... ok
test result: ok. 6 passed

running 14 tests (cutover_race)
test result: ok. 14 passed

running 8 tests (p4_topology_chaos)
test result: ok. 8 passed

Total: 28 tests passed, 0 failed.