qa-cache-testing

Read-only specialist that scans application code for cache-key collision risks - keys that should be unique per (tenant, user, locale, region) but aren't. Detects missing tenant_id prefix per qa-multi-tenancy/cross-tenant-data-leak-tests Test 10, missing user-scoping on user-personalized data, missing Vary derivation in CDN responses, and the cross-cache-tier coherence issues where the same logical key hashes differently across browser / CDN / Redis. Use proactively when reviewing a PR that touches cache.set / cache.get / memoization decorators, or when investigating 'one user sees another user's data' reports. Preloads cache-coherence-patterns-reference.

Wraps browser-side Cache-Control testing patterns using Playwright (and Cypress for legacy stacks): verifying response Cache-Control headers from Network events, asserting ETag round-trips (request includes If-None-Match → server returns 304), testing service-worker cache strategies (Workbox cacheFirst / networkFirst / staleWhileRevalidate), and verifying browser cache behavior under reload (normal reload vs hard reload semantics). Covers MDN's Cache-Control semantics + RFC 9111. Use when designing browser-cache-respecting endpoints or auditing caching behaviour in E2E tests.

Pure-reference catalog of cache-coherence patterns across the request path. Covers the canonical RFC 9111 directives (Cache-Control: max-age, s-maxage, no-cache, no-store, must-revalidate, private/public, immutable; Vary for key derivation; ETag + If-None-Match revalidation), the layered-cache discipline (browser → CDN → reverse-proxy → application → data store), per-tier coherence patterns (write-through, write-back, write-around, cache-aside), and the canonical invalidation strategies (TTL-only, event-driven purge, surrogate keys, version-tagged keys). Use as the cache-design reference when picking patterns or auditing an existing setup. Consumed by redis-cache-tests, cdn-cache-purge-tests, varnish-test-vtc-syntax, browser-cache-control-tests, cache-key-collision-detector.

Pure-reference catalog of cache-stampede (thundering-herd) phenomena and mitigations. Defines the stampede (massively-parallel cache misses on key expiry trigger simultaneous recomputation, often congestion-collapse) and the three canonical mitigation families: locking (one writer recomputes, others wait or serve stale), external recomputation (a separate process refreshes on schedule or near-expiry), and probabilistic early expiration via XFetch (each requester independently decides to refresh with probability rising toward expiry; uses formula `(time() - delta * beta * log(rand(0,1))) >= expiry`). Use when designing cache-refresh strategy or diagnosing a known stampede incident. Composes cache-coherence-patterns-reference + stale-while-revalidate-reference.

Wraps CDN cache-purge testing patterns for Cloudflare (POST /zones/{zone_id}/purge_cache, single-file / everything / cache-tags / hostname / prefix), Fastly (POST purge-by-key / purge-all, surrogate-keys via Surrogate-Key header), and CloudFront (CreateInvalidation API + paths). Covers end-to-end test patterns (write origin → trigger purge → assert edge serves fresh), purge-propagation delay testing (typically 1-30s globally), surrogate-key + cache-tag patterns for group-purge, and Cache-Status header verification (cf-cache-status: HIT/MISS/BYPASS). Use when designing or auditing CDN cache-invalidation workflows.

Wraps Memcached cache testing patterns: text and binary protocol command verification (set/get/add/cas/incr/decr), TTL semantics (0=never-expire, 30-day Unix-timestamp boundary), no-persistence and LRU eviction under memory pressure, consistent-hashing client key distribution across nodes, and AWS ElastiCache Memcached Auto Discovery endpoint testing. Use when writing tests for an application that uses Memcached as its primary cache, when verifying ElastiCache Memcached cluster behaviour, or when contrasting Memcached eviction and distribution semantics against Redis.