Version availability cache payloads without flushing every tenant at once
A response-field change makes older cached payloads unreadable. Flushing all keys would force a simultaneous cold start across the service.
- Focused work estimate
- 3h + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Schema compatibility · Cache rollout
Estimated field mix
- Platform engineering40%
- API design30%
- Performance 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 equipment-rental service caches availability summaries. A campaign sends repeated reads, while stock updates and shared expiry times create bursts against the origin. Build a local origin stub and cache-backed read API using synthetic depots and products.
Setup prerequisites
- Create a deterministic local availability origin and Redis-backed reader with synthetic tenant, depot and product data.
- Use a seeded hot-key distribution and controlled time; record cache capacity, TTLs, runtime and machine limits.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- PCACHE-101 · Specify which availability responses may be reused
- PCACHE-102 · Measure saved origin work instead of celebrating the hit ratio
- PCACHE-103 · Create a hot-key workload that exposes synchronized expiry
- PCACHE-105 · Spread cache refill times without extending the freshness ceiling
- PCACHE-104 · Coalesce simultaneous availability misses for one key
- PCACHE-106 · Serve stale availability only within an explicit degraded-read policy
- PCACHE-107 · Prevent a delayed refill from restoring availability older than an update
Acceptance criteria
- Write a new payload/key version and reject incompatible old payloads safely.
- Define a bounded warming or lazy-fill strategy and retain per-tenant scope.
- Make rollback behavior explicit when older readers encounter values written during the new release.
Implementation constraints
- Treat cache payloads as derived data; do not migrate authoritative stock records as part of this change.
Verification to include
- Run old and new readers against mixed-version fixtures and verify the documented compatibility behavior.
- Switch versions under the hot-key workload and measure origin refill concurrency without a global flush.
Deliverables
- Payload-version contract, compatibility tests and rollout procedure
Rollout and recovery
Canary a small synthetic tenant set, then expand; rollback restores the prior namespace and lets unused versioned entries expire.
Value of the work
For the engineer: Learn to evaluate caching through avoided work, bounded staleness, concurrency and recovery rather than hit rate alone.
For the team: Produce a reviewable cache policy and failure exercise for a read-heavy service with changing business data.
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.