Skill: Caching

Read the bundled conventions before applying this skill.

Decisions that affect behavior

• Identify the layer being changed: data values, query results/schema metadata, rendered fragments/pages, or HTTP validators. They have different keys and invalidation contracts. A backend change does not automatically refresh every layer, and a warm cache is not evidence of fresh data.
• Preserve the configured backend and component ID unless replacement is required. Yii 22.0 uses ApcuCache without useApcu; ApcCache, XCache, ZendDataCache, and the old mget/mset/madd aliases are removed. Use multiGet/multiSet/ multiAdd and Dependency::isChanged(). Extensions such as Redis must be resolved separately from core; availability depends on runtime and deployment.
• Include every input that changes the cached value in its key or variations, including relevant tenant/user, authorization scope, locale, and query parameters. Do not cache personalized output under a public shared key. Keep current key prefix conventions and account for processes sharing the backend.
• get() uses false for a miss/expiry/changed dependency; getOrSet() therefore recomputes a legitimate false result. Use an explicit value envelope when false is a meaningful cached result. exists() does not check dependency freshness.
• Dependencies are evaluated when set and checked on retrieval; disabling the serializer disables dependency handling. Select TTL, tags, or a dependency that represents the actual source change. Verify invalidation on relevant writes; do not assume a transaction or record event clears an unrelated cached result.
• Page/fragment caching must preserve the requested dynamic content and vary by relevant request context. HTTP caching must preserve cache-control/privacy and conditional-request semantics. Treat schema-cache refresh separately after DDL.
• getOrSet() is not a lock or guarantee of single computation under concurrency. Do not use it to enforce uniqueness or serialize side effects. Do not flush a shared cache as an ordinary acceptance check; invalidation should be scoped.

Observable acceptance

With isolated keys or a disposable backend, demonstrate miss, hit without repeated computation, expiry or chosen dependency invalidation, and a fresh result after the source changes. Check isolation between contexts represented in the key. Exercise a meaningful false value if applicable. For HTTP caching verify a full response and the corresponding conditional response, including relevant headers; for page or fragment caching verify dynamic portions and authorized variants remain correct. Report whether the production backend/SAPI was exercised or only an in-memory double.

Evidence routes

Read framework/caching/{Cache,Dependency,TagDependency,ApcuCache}.php, framework/widgets/FragmentCache.php, framework/filters/{PageCache,HttpCache}.php, and query/schema cache integration in framework/db/Connection.php and Schema.php. Tests: tests/framework/caching/CacheTestCase.php, TagDependencyTest.php and FileCacheTest.php in that directory, tests/framework/widgets/FragmentCacheTest.php, tests/framework/filters/PageCacheTest.php, and HttpCacheTest.php. Guides: caching-data, caching-fragment, caching-page, caching-http.

Install and activate this skill

Select yii2-caching in the installation and client verification guide. Install the complete bundle, including referenced resources. The canonical SKILL.md is also available for direct reading.

Continue with the related framework guide.