Coalesce concurrent archive cache fills for one blob
Ten simultaneous misses download the same object ten times. Share one fill without joining unrelated keys.
- Focused work estimate
- 2h 45m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Concurrency · Resource management
Estimated field mix
- Performance engineering50%
- Storage systems50%
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
Fictional media archive Ash serves generated byte fixtures through a fast local cache and slower provider stub. Both tiers run locally.
Setup prerequisites
- Create immutable generated blobs with known digests.
- Implement controllable cache and origin adapters with read failures.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Same identity shares fill
- Different identities remain independent
- Failure releases waiters consistently
Implementation constraints
- Bound the in-flight map and clear settled entries.
Verification to include
- Issue concurrent same-key reads
- Fail shared fill then retry
Deliverables
- Fill coordinator and concurrency cases
Rollout and recovery
Disable coalescing if waiters cannot be released.
Value of the work
For the engineer: Practice cache correctness, request coalescing and capacity control.
For the team: Inspect whether faster delivery preserves bytes and operating limits.
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.