Deliver database changes as versioned migrations that preserve backward compatibility across application versions and delay destructive cleanup until evidence permits it.

What you will be able to do

Distinguish migration script from expansion state in a realistic database changes and backward compatibility case.
Interpret the delivery evidence and boundary associated with compatible service.
Choose an appropriate action involving data transition without exceeding the named operational scope.
Verify removal gate through an observable service result and reproducible handoff.

Frame Database Changes and Backward Compatibility

Deliver database changes as versioned migrations that preserve backward compatibility across application versions and delay destructive cleanup until evidence permits it.

A customer name field must split into first and last name while old and new application instances may run together during a progressive release.

Keep the delivery target, declared intent, execution evidence, reliability boundary, and recovery choice separate. Start with observable state and preserve enough context for another operator to reproduce the decision.

Migration script

A migration script stores a database change in version control with an ordered identity. Within database changes and backward compatibility, this role answers a separate delivery or reliability question and keeps its own evidence.

Add the new name columns through one reviewed migration. Apply that action to the named service case before widening the rollout, infrastructure scope, or incident response.

Respect this boundary: do not make production-only schema edits outside the delivery record. The observable result is specific: each environment reports the same migration identity.

Expansion state

An expansion change adds compatible structures before removing the existing representation. Within database changes and backward compatibility, this role answers a separate delivery or reliability question and keeps its own evidence.

Add new columns while retaining the original name field. Apply that action to the named service case before widening the rollout, infrastructure scope, or incident response.

Respect this boundary: do not rename or delete the old field in the first release. The observable result is specific: both application versions can operate during rollout.

Compatible service

Backward-compatible application code tolerates the schema states that coexist during deployment. Within database changes and backward compatibility, this role answers a separate delivery or reliability question and keeps its own evidence.

Read the new fields when present and preserve the old path temporarily. Apply that action to the named service case before widening the rollout, infrastructure scope, or incident response.

Respect this boundary: do not require all instances to switch at the same instant. The observable result is specific: old and new instances serve requests against the expanded schema.

Data transition

A data transition moves or derives existing values while compatibility remains available. Within database changes and backward compatibility, this role answers a separate delivery or reliability question and keeps its own evidence.

Backfill the new columns with measurable progress and retry behavior. Apply that action to the named service case before widening the rollout, infrastructure scope, or incident response.

Respect this boundary: do not combine an unbounded backfill with a blocking release step. The observable result is specific: existing customer records gain valid new values.

Removal gate

A contraction removes old structures only after no supported code depends on them. Within database changes and backward compatibility, this role answers a separate delivery or reliability question and keeps its own evidence.

Verify reads, writes, rollback needs, and deployment completion before cleanup. Apply that action to the named service case before widening the rollout, infrastructure scope, or incident response.

Respect this boundary: do not remove the old field while rollback still requires it. The observable result is specific: the obsolete column is removed in a later safe migration.

Apply Database Changes and Backward Compatibility to One Service Change

Use one bounded delivery decision: A customer name field must split into first and last name while old and new application instances may run together during a progressive release.

First, add the new name columns through one reviewed migration. Then, add new columns while retaining the original name field. Keep both observations attached to the exact revision, environment, or service window.

Next, read the new fields when present and preserve the old path temporarily. After that, backfill the new columns with measurable progress and retry behavior. Close the work only after you verify reads, writes, rollback needs, and deployment completion before cleanup.

Recap Before Practice and Prove

Migration script: A migration script stores a database change in version control with an ordered identity. In this service case, add the new name columns through one reviewed migration. Preserve the boundary: do not make production-only schema edits outside the delivery record.

Expansion state: An expansion change adds compatible structures before removing the existing representation. In this service case, add new columns while retaining the original name field. Preserve the boundary: do not rename or delete the old field in the first release.

Compatible service: Backward-compatible application code tolerates the schema states that coexist during deployment. In this service case, read the new fields when present and preserve the old path temporarily. Preserve the boundary: do not require all instances to switch at the same instant.

Data transition: A data transition moves or derives existing values while compatibility remains available. In this service case, backfill the new columns with measurable progress and retry behavior. Preserve the boundary: do not combine an unbounded backfill with a blocking release step.

Removal gate: A contraction removes old structures only after no supported code depends on them. In this service case, verify reads, writes, rollback needs, and deployment completion before cleanup. Preserve the boundary: do not remove the old field while rollback still requires it.