Backend Migrations

Create and manage database migrations with reversible up/down methods, focused changes, and zero-downtime deployment considerations. Use this skill when creating or modifying migration files in directories like migrations/, db/migrate/, alembic/versions/, sequelize/migrations/, prisma/migrations/, or any database schema versioning folders. Use this when adding or altering database tables, columns, indexes, foreign keys, or constraints in migration scripts, implementing both up (apply changes) and down (rollback changes) methods for reversible migrations that allow safe rollbacks if deployments fail, writing migration scripts for ORMs and migration tools like Sequelize, Alembic, Django migrations, Rails migrations, TypeORM, Prisma migrations, Knex.js migrations, or any database migration framework, creating database indexes on large tables using concurrent creation options like CREATE INDEX CONCURRENTLY in PostgreSQL to avoid table locks that would block production traffic during deployment, separating schema migrations (structural changes like adding columns or tables) from data migrations (transforming or populating data) for safer rollbacks and clearer change tracking, planning backwards-compatible schema changes for zero-downtime deployments in high-availability systems where old and new code versions run simultaneously during rolling deployments, ensuring each migration file contains small focused changes for a single logical purpose (one migration per table change or related group of changes) to make troubleshooting and rollbacks easier, using clear descriptive naming conventions with timestamps that indicate what the migration does (like 20250101_add_email_to_users or 2025_01_01_create_products_table), ensuring migrations are never modified after being committed and deployed to version control since changing deployed migrations can cause inconsistencies across environments, and managing migration execution order carefully for database consistency especially when multiple developers are creating migrations concurrently or when merging feature branches.