safe-migrations

Zero-downtime PostgreSQL migrations in Django use the Expand-and-Contract pattern to split schema changes into pre- and post-migration phases, avoiding long table locks by adding nullable columns first and finalizing constraints later.

Backfilling data in large PostgreSQL tables during Django migrations is done in small chunks or batches, ensuring idempotence to prevent locking issues and allowing safe processing without blocking concurrent database operations.

Safe column renames and removals in Django use SeparateDatabaseAndState to decouple schema state from database operations, allowing multi-phase deployments that prevent downtime and lock conflicts on large PostgreSQL tables.

Concurrent index creation in PostgreSQL during Django migrations is supported by using specific lock management patterns and two-phase constraint validation, ensuring indexes are built without blocking writes or causing deployment downtime.

The Expand-and-Contract pattern for Django schema changes splits deployment into pre- and post-migration phases: first expanding by adding new nullable columns or tables, then contracting by removing old columns after application code fully transitions.

Safe Django migrations on PostgreSQL require lock management settings like lock_timeout and concurrent index operations to prevent blocking transactions, ensuring long-running schema changes do not lock out concurrent database access.