Report archive cache hit rates with a defined denominator
Dashboard hit rate counts every chunk and exaggerates cache usefulness. Count logical read outcomes explicitly.
- Focused work estimate
- 1h 45m + prerequisites
- Priority in the scenario
- Low
- Engineering practice
- Observability · Measurement
Estimated field mix
- Site reliability50%
- Performance engineering30%
- Storage systems20%
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.
- CTIER-101 · Keep archive cache misses distinct from provider failures
- CTIER-102 · Key archive cache entries by immutable blob identity
- CTIER-103 · Verify archive cache fills before promoting temporary bytes
- CTIER-104 · Coalesce concurrent archive cache fills for one blob
- CTIER-105 · Enforce archive cache capacity before admitting a fill
- CTIER-106 · Avoid evicting archive blobs while active readers hold them
- CTIER-107 · Record archive cache recency without writing on every byte read
- CTIER-108 · Detect corrupted archive cache entries before serving them again
- CTIER-109 · Reconcile archive cache metadata after process restart
Acceptance criteria
- Denominator is logical read attempts
- Bypass and errors are separate
- No blob content enters events
Implementation constraints
- Report local measurements without generalized performance claims.
Verification to include
- Read hit miss and bypass fixtures
- Retry failed read and inspect counts
Deliverables
- Metrics contract and captured examples
Rollout and recovery
Hide hit-rate panel if event accounting changes.
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.