Expand-contract migration.

also: expand-contract · expand and contract · expand/contract · parallel change

Changing a schema in backward-compatible phases: add the new structure, migrate and dual-write, switch reads, then remove the old.

the two-minute refresher

A direct column rename breaks whichever code version is still running mid-deploy.
Expand: add the new column, write both, read the old.
Migrate: backfill, switch reads to the new column, keep writing both.
Contract: stop writing the old column, then drop it.

also: expand-contract · expand and contract · expand/contract · parallel change

Changing a schema in backward-compatible phases: add the new structure, migrate and dual-write, switch reads, then remove the old.

A direct column rename breaks whichever code version is still running mid-deploy.
Expand: add the new column, write both, read the old.
Migrate: backfill, switch reads to the new column, keep writing both.
Contract: stop writing the old column, then drop it.