Retire legacy customer references only after a rollback rehearsal
Dropping old columns would end binary rollback to old readers, but the release checklist does not mention that boundary.
- Focused work estimate
- 5h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Migration planning · Recovery
Estimated field mix
- Database engineering60%
- Platform engineering40%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional support platform stores a mutable external account code as its primary relationship key. Renames and imports now break references in several tables.
Setup prerequisites
- Create a disposable database with synthetic customers and dependent records.
- Apply real migration files; never use production db push.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- AMIGRATE-101 · Inventory every reference to the mutable customer code
- AMIGRATE-102 · Add immutable customer IDs through an additive migration
- AMIGRATE-103 · Add nullable customer-ID references to dependent tables
- AMIGRATE-104 · Backfill customer IDs with resumable keyset batches
- AMIGRATE-105 · Bridge legacy customer writes to the new identity transactionally
- AMIGRATE-106 · Protect customer-code renames during the backfill window
- AMIGRATE-107 · Verify relationship completeness before making customer IDs mandatory
- AMIGRATE-108 · Validate and enforce the new customer relationship constraints
- AMIGRATE-109 · Switch customer reads to immutable IDs with a compatibility fallback plan
Acceptance criteria
- Inventory remaining legacy reads and writes before contraction.
- Rehearse the last reversible rollback with compatible code.
- Document the point after which forward repair is required.
Implementation constraints
- Do not drop columns merely because the backfill command completed.
Verification to include
- Run the old-compatible build against the expanded schema.
- Attempt the contraction readiness check with one legacy writer and verify it blocks.
Deliverables
- Contraction migration plan and rollback evidence
Rollout and recovery
Apply contraction only after reviewed readiness; preserve a tested backup and forward-repair procedure.
Value of the work
For the engineer: Practice migration ordering, compatibility and referential integrity.
For the team: Review a reversible schema transition with measurable completeness checks.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.