Claim one pending job atomically under competing pollers
Two polling clients select the same pending job before either writes its assignment.
- Focused work estimate
- 4h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Row locking · Transactions
Estimated field mix
- Database engineering100%
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 inspection service assigns review jobs to staff. Polling clients sometimes claim the same job and a disconnected client can finish work after reassignment.
Setup prerequisites
- Create synthetic jobs and two independent database clients.
- Use explicit state methods and an injected clock.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Select and transition a job within one transaction.
- Use a database locking strategy with documented contention behavior.
- Return distinct jobs or no work under concurrent pollers.
Implementation constraints
- Evaluate SKIP LOCKED against the declared ordering and fairness policy.
Verification to include
- Start two clients at a barrier and assert unique claimed identities.
- Hold one candidate lock and verify the documented skip or wait behavior.
Deliverables
- Atomic claim query and concurrency test
Rollout and recovery
Canary with two synthetic pollers; reduce concurrency if lock behavior violates the contract.
Value of the work
For the engineer: Practice database concurrency, leases and transactional invariants.
For the team: Review whether assignment authority remains reliable during contention and recovery.
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.