Caching Strategies — Detailed

flowchart TB
  subgraph Tiers[Cache Tiers]
    B[Browser Cache]
    CDN[CDN / Edge Cache]
    REV[Reverse Proxy<br/>Varnish/NGINX]
    APP[App Local<br/>Caffeine/Guava]
    DC[Distributed Cache<br/>Redis/Memcached]
    DBC[DB Buffer Pool]
  end

  subgraph Patterns[Patterns]
    CA[Cache-Aside<br/>look-aside]
    RT[Read-Through]
    WT[Write-Through]
    WB[Write-Back<br/>write-behind]
    WA[Write-Around]
    REF[Refresh-Ahead]
  end

  subgraph Eviction[Eviction]
    LRU
    LFU
    TLRU[TTL+LRU]
    ARC
    TwoQ[2Q / TinyLFU]
  end

  subgraph Failures[Failure Modes]
    STAMP[Cache Stampede<br/>thundering herd]
    PEN[Cache Penetration<br/>key never exists]
    AVAL[Cache Avalanche<br/>mass expiry]
    INV[Stale data /<br/>invalidation bugs]
  end

  subgraph Mitigations[Mitigations]
    LOCK[Single-flight /<br/>distributed lock]
    BLOOM[Bloom filter for<br/>missing keys]
    JIT[Jittered TTL]
    NEG[Negative caching]
    VER[Versioned keys]
  end

  Client --> B --> CDN --> REV --> APP --> DC --> DBC
  Client --> Patterns
  Patterns --> Eviction
  Failures --- Mitigations
  STAMP -.->|fix| LOCK
  PEN -.->|fix| BLOOM
  PEN -.->|fix| NEG
  AVAL -.->|fix| JIT
  INV -.->|fix| VER

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class CDN,REV edge;
    class CA,RT,WT,WB,WA,REF,TLRU,STAMP,PEN,AVAL,INV,LOCK,BLOOM,JIT,NEG,VER service;
    class B,APP,DC,DBC,TwoQ cache;

Pattern semantics

Pattern	Read	Write	Notes
Cache-aside	app reads cache, falls back to DB, fills cache	app writes DB, invalidates cache	most common
Read-through	cache transparently loads from DB on miss	—	cache library does the load
Write-through	—	app writes cache → cache writes DB synchronously	consistent, slower writes
Write-back	—	app writes cache → cache async-flushes to DB	fast writes, durability risk
Write-around	—	app writes DB, cache filled lazily on read	avoids cache pollution by one-time writes
Refresh-ahead	proactively refresh hot keys before TTL	—	predictive

Invalidation

• TTL (simplest, drifts).
• Explicit on write (DEL, pub/sub).
• Versioned key (user:42:v17) — never invalidate, just bump version.
• Change-Data-Capture (Debezium) → cache invalidator.

Glossary & fundamentals

Concepts referenced in this design. Each row links to its canonical page; the tag column shows whether it is a high-level (HLD) or low-level (LLD) concept.

Tag	Concept	What it is	Page
HLD	Load balancer / GSLB	L4/L7 traffic distribution and failover	load-balancer
HLD	CDN	edge caching for static assets	cdn
HLD	Cache strategies	cache-aside, read/write-through, eviction	caching-strategies
HLD	Pub/Sub & message brokers	topics, consumer groups, delivery semantics	pub-sub-pattern
HLD	Probabilistic data structures	Bloom, HLL, Count-Min, MinHash, t-digest	probabilistic-data-structures
HLD	Idempotency & retries	safe re-execution, backoff + jitter	idempotency-retries
HLD	Change Data Capture	WAL/binlog tailing, outbox publishing	change-data-capture
LLD	Structural patterns	Adapter, Decorator, Facade, Proxy, Composite	structural-patterns