Which technique enables zero-downtime database schema changes?

Which technique enables zero-downtime database schema changes?

• A. Backward-compatible online migrations with feature-flagging
• B. Full downtime migrations with no planning
• C. Patching in-place without versioning
• D. Removing all backups prior to changes

Answer: (A)

Zero-downtime database schema changes rely on making updates in a way that keeps existing code functioning while the new version is rolled out. The best approach is backward-compatible online migrations combined with feature flags. By designing changes to be non-breaking—adding new columns that can be null, introducing new tables or versions, and avoiding immediate destructive edits—old code keeps working while the new code path is prepared. Using feature flags lets you gradually switch traffic from the old schema path to the new one, test in production, and roll back if issues arise without taking the system offline. Over time, you deprecate the old path as all clients adopt the new schema. Other approaches don’t fit zero-downtime goals: migrating with no planning can cause unexpected downtime, patching in-place without versioning risks breaking compatibility or leaving you with inconsistent states, and deleting backups beforehand offers no protection and isn’t related to keeping services online.

Zero-downtime database schema changes rely on making updates in a way that keeps existing code functioning while the new version is rolled out. The best approach is backward-compatible online migrations combined with feature flags. By designing changes to be non-breaking—adding new columns that can be null, introducing new tables or versions, and avoiding immediate destructive edits—old code keeps working while the new code path is prepared. Using feature flags lets you gradually switch traffic from the old schema path to the new one, test in production, and roll back if issues arise without taking the system offline. Over time, you deprecate the old path as all clients adopt the new schema.

Other approaches don’t fit zero-downtime goals: migrating with no planning can cause unexpected downtime, patching in-place without versioning risks breaking compatibility or leaving you with inconsistent states, and deleting backups beforehand offers no protection and isn’t related to keeping services online.