Two versions of an application run concurrently during migration. The new version renames a database field that the old version still requires. Which rollout pattern best preserves compatibility?

1. Assume a rolling deployment means both versions never overlap.
2. Introduce a backward-compatible schema, migrate readers and writers in stages, then remove the old field after validation.
3. Drop the old field before any old application instances are drained.
4. Disable database backups and ignore rollback requirements.