Zero-Downtime Database Migrations: Our Playbook

Database migrations are one of the scariest operations in production. We developed a systematic approach that has let us ship hundreds of migrations without a single minute of downtime.

The Golden Rules

• Never rename or drop a column in a single deployment
• Always add new columns as nullable or with a default
• Use concurrent index creation to avoid table locks
• Backfill data in batches, never in a single transaction
• Keep migrations idempotent so they can be safely re-run

“The best migration is one your users never know happened.”

— Database Team