ngxtm/devkit/caching

Caching & Redis Standards

Caching Strategy

• Layering: Use Multi-Level Caching for high-traffic read endpoints.
• L1 (Local): In-Memory (Node.js heap). Ultra-fast, no network. Ideal for config/static data. Use lru-cache.
• L2 (Distributed): Redis. Shared across pods.
• Pattern: Implement Stale-While-Revalidate where possible to avoid latency spikes during cache misses.

NestJS Implementation

• Library: Use cache-manager with cache-manager-redis-yet (Recommended over cache-manager-redis-store for better V4 support and stability).
• Interceptors: Use @UseInterceptors(CacheInterceptor) for simple GET responses.
• Warning: By default, this uses the URL as the key. Ensure consistent query param ordering or custom key generators.
• Decorators: Standardize custom cache keys.

``typescript @CacheKey('users_list') @CacheTTL(300) // 5 minutes findAll() { ... } ``

Redis Data Structures (Expert)

• Don't just use GET/SET.
• Hash (`HSET`): Storing objects (User profiles). Allows partial updates (HSET user:1 lastLogin result) without serialization overhead.
• Set (`SADD`): Unique collections (e.g., "Online User IDs"). O(1) membership checks.
• Sorted Set (`ZADD`): Priority queues, Leaderboards, or Rate Limiting windows.

Invalidation Patterns

• Problem: "There are only two hard things in Computer Science: cache invalidation and naming things."
• Tagging: Since Redis doesn't support wildcards efficiently (KEYS is O(N) - bans in PROD), use Sets to group keys.
• _Create_: SADD post:1:tags cache:post:1
• _Invalidate_: Fetch tags from Set, then DEL usage keys.
• Event-Driven: Listen to Domain Events (UserUpdated) to trigger invalidation asynchronously.

Stampede Protection

• Jitter: Add random variance to TTLs (e.g., 300s ± 10s) to prevent all keys expiring simultaneously.
• Locking: If a key is missing, one process computes it while others wait or return stale. (Complex, often handled by swr libraries).