07 — Caching Strategies

flowchart LR
    User["User Request"] --> App["Application Server"]
    App --> Cache["Cache Layer<br/>Redis / Memcached / CDN"]

    Cache -->|"Cache Hit ✅"| App
    Cache -->|"Cache Miss ❌"| DB["Database"]
    DB --> App
    App --> User
    App -->|"Update cache"| Cache

    style User fill:#f59e0b,color:#fff
    style App fill:#3b82f6,color:#fff
    style Cache fill:#7c3aed,color:#fff
    style DB fill:#059669,color:#fff

flowchart TB
    Strategies["Caching Strategies"] --> CacheAside["Cache-Aside<br/>App checks cache first,<br/>then database"]
    Strategies --> ReadThrough["Read-Through<br/>Cache layer handles DB queries<br/>transparently to app"]
    Strategies --> WriteAround["Write-Around<br/>Write to DB, invalidate cache<br/>Read next time"]
    Strategies --> WriteThrough["Write-Through<br/>Write to cache AND DB<br/>Always consistent"]
    Strategies --> WriteBack["Write-Behind<br/>Write to cache first,<br/>async write to DB later"]
    Strategies --> RefreshAhead["Refresh-Ahead<br/>Cache auto-refreshes<br/>before expiration"]

    style Strategies fill:#7c3aed,color:#fff
    style CacheAside fill:#3b82f6,color:#fff
    style ReadThrough fill:#059669,color:#fff
    style WriteAround fill:#f59e0b,color:#fff
    style WriteThrough fill:#ef4444,color:#fff
    style WriteBack fill:#6366f1,color:#fff
    style RefreshAhead fill:#10b981,color:#fff

sequenceDiagram
    participant App as Application
    participant Cache as Redis Cache
    participant DB as Database

    App->>Cache: GET user:123
    Cache-->>App: MISS

    App->>DB: SELECT * FROM users WHERE id=123
    DB-->>App: { name: "Alice" }

    App->>Cache: SET user:123 { name: "Alice" } TTL 3600
    App-->>User: Response

    Note over App,DB: Next request for same user...

    App->>Cache: GET user:123
    Cache-->>App: { name: "Alice" } ✅ HIT
    App-->>User: Fast response

flowchart TB
    User["🌍 User"] --> Edge["CDN Edge Server<br/>Closest to user"]
    Edge -->|"Cache MISS"| Origin["Origin Server<br/>Primary data source"]
    Origin --> Edge
    Edge --> User

    subgraph EdgeStorage["Edge Cache"]
        Static["Static assets<br/>Images, CSS, JS<br/>Long TTL"]
        Dynamic["Dynamic content<br/>HTML pages, API<br/>Short TTL"]
    end

    style User fill:#f59e0b,color:#fff
    style Edge fill:#7c3aed,color:#fff
    style Origin fill:#3b82f6,color:#fff