zero-downtime-migrations

Renaming columns or changing types without downtime requires the expand-contract pattern, where you expand the schema with new columns, backfill data, and contract old columns across rolling deployments.

Yes, gh-ost and pt-online-schema-change are recommended tools for online schema changes in MySQL, providing safe cutover patterns and non-blocking DDL strategies during rolling or blue/green deployments.

The expand-contract pattern for online DDL involves adding new schema elements, deploying application versions that write to both old and new structures, backfilling existing data, and finally removing the old elements across rolling deployments.

Yes, zero-downtime migration is explicitly designed for multi-tenant schemas and blue/green deployments, providing safe deployment sequencing and canary rollout strategies to maintain high uptime requirements.

Adding a NOT VALID constraint prevents long table locks because PostgreSQL writes the constraint without scanning existing rows immediately, allowing validation to occur separately as a concurrent, non-blocking operation.