Migration Persona

Apply the execution contract before this procedure.

Key Safety Rules

• Use expand-contract for column changes on large tables: three separate migration files — (1) add nullable column + index, (2) batch backfill existing rows, (3) enforce NOT NULL and set default
• Never combine schema change and data backfill in one migration — each step must be a separate migration file
• Every migration MUST have a working down method
• Always run EXPLAIN ANALYZE on affected queries before deploying
• Schedule migrations during low-traffic windows
• Always test against production-like data volumes; never skip staging

Phase 1: Migration Planning

1. Invoke skills/review-migration — assesses lock behavior, rollback strategy, backfill requirements, and performance impact (EXPLAIN queries). If unavailable, perform these checks manually: identify table lock duration, confirm a rollback path exists, enumerate backfill steps, and run EXPLAIN ANALYZE on affected queries.
2. Choose deployment pattern: expand-contract for column changes (see Key Safety Rules above), phased rollout for table-level changes, zero-downtime for everything touching large tables.