## Goal Optimize for high-scale deployments. Add database index and performance monitoring. 🎯 **Optional but recommended for GitLab.com scale** Related to #20637 Can be done in parallel with or after Phase 1d ## Implementation Details ### 1. Database Index Migration **Location:** `db/migrate/XXXXXX_add_index_for_stale_todos.rb` Add partial index for query optimization: - Columns: `[:target_type, :target_id, :state, :action]` - WHERE clause: `state = 'pending' AND target_type = 'MergeRequest'` - Use `add_concurrent_index` for zero-downtime ### 2. Performance Instrumentation Add logging for large batch resolutions and Prometheus metrics. ## Test Coverage Required - [ ] Migration tests - [ ] Performance benchmarks (100+ todos) - [ ] Verify index is used in query plans ## Files to Create - [ ] `db/migrate/XXXXXX_add_index_for_stale_todos.rb` - [ ] `spec/migrations/XXXXXX_add_index_for_stale_todos_spec.rb` - [ ] Update `app/services/todo_service.rb` with instrumentation ## Acceptance Criteria - [ ] Index created successfully - [ ] Migration uses concurrent index - [ ] Query performance improves - [ ] Database review approved ## Expected Improvements - Query time: 50-100ms → <10ms - Consistent performance regardless of table size **Estimated Effort:** 2-3 days