database-migration-planner

To safely rename a column in a live PostgreSQL database, use the expand-contract pattern to add the new column, migrate data, and drop the old structure later. This prevents long locks and downtime.

The expand-contract pattern for database schema changes safely adds new structures before removing old ones. It separates migrations into expand and contract phases to prevent data corruption and long locks.

Write a rollback plan for DDL operations by defining explicit reversal steps for each expand and contract phase. This ensures database normalization and indexing changes remain reversible without data loss.

You need SQLAlchemy and psycopg2 to plan database migrations because this Skill requires Python scripting and PostgreSQL connectivity to characterize tables and verify database safety before contracting.

Identify lock tiers before executing DDL by characterizing tables and evaluating schema change requirements. This determines the database safety level and helps structure expand-contract migration steps.

A limitation of using expand-contract migrations is that completing schema changes requires multiple deployment phases. You must verify data integrity before the contract phase, making immediate cutover impossible.