Split existing stock rows by warehouse without a write outage
The old table has one quantity per SKU. The East/West launch needs a warehouse key, but a one-shot table rewrite blocks checkout on the large synthetic inventory fixture.
- Focused work estimate
- 5h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Schema evolution · Online migrations · Compatibility · Database operations
Estimated field mix
- Database engineering70%
- Platform engineering30%
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 retailer sells bicycle parts from East and West warehouses. Cart reservations last ten minutes, payment callbacks arrive late, and warehouse counts occasionally need correction. The exercise has no real orders or payment integration.
Setup prerequisites
- Relational modeling
- Concurrent API requests
- State transitions
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Provide expand, backfill, validation, and contract steps with explicit compatibility windows.
- Backfill is resumable and preserves total on-hand quantities.
- Demonstrate old and new application versions coexist during the supported migration window.
Implementation constraints
- Define the mapping of legacy stock to East before backfill; never infer a warehouse from a SKU.
Verification to include
- Interrupt the backfill and resume without duplicate inventory.
- Run reservation traffic during migration and test rollback before the contract step.
Deliverables
- Versioned migration set and measured lock-duration report
Rollout and recovery
Use the documented expand/backfill/switch sequence; prohibit old-version rollback after incompatible cleanup.
Value of the work
For the engineer: Practice inventory invariants and timed state transitions while balancing customer experience with operational repair.
For the team: Inspect an engineer's handling of overselling, delayed callbacks, warehouse boundaries, and reversible schema changes.
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.