How do you implement distributed caching patterns: Cache-Aside, Write-Through, Write-Behind, and Refresh-Ahead?

Caching reduces database read load and minimizes network latency. Choosing the correct caching pattern depends on whether your workload is read-heavy or write-heavy, and how much data inconsistency your business logic tolerates.\n\n### 1. Cache-Aside (Lazy Loading)\nThe application code is explicitly responsible for reading and writing to both the cache and the database.\n* Read Flow: App checks Cache. If Hit, return. If Miss, read from Database, write to Cache, and return.\n* Write Flow: App writes directly to Database, then invalidates (deletes) the cache key.\n* Pros: Cache only contains active hot data; node failures do not corrupt state.\n* Cons: Initial Cache Miss incurs 3 network round-trips; small risk of stale reads during concurrent writes.\n\n### 2. Write-Through\nThe application writes exclusively to the Cache. The Cache synchronously writes to the Database before acknowledging success to the caller.\n* Pros: Cache is never stale; data is immediately available for subsequent reads.\n* Cons: Write latency is doubled (sum of cache write + DB write); stores data that may never be read again.\n\n### 3. Write-Behind (Write-Back)\nThe application writes to the Cache and immediately receives a success confirmation. The Cache asynchronously batches writes and flushes them to the Database in the background.\n* Pros: Ultra-fast write performance; absorbs immense write spikes.\n* Cons: Risk of permanent data loss if the cache server crashes before flushing dirty buffers to the database.\n\n### 4. Refresh-Ahead\nThe Cache automatically reloads frequently accessed keys from the Database before they reach their TTL expiration.\n* Pros: Hot keys never suffer Cache Miss latency penalties.\n* Cons: Inaccurate access predictions waste database query capacity.\n\n### Key Architectural Comparison\n| Pattern | Write Latency | Read Latency on Hit | Stale Data Risk | Risk of Data Loss |

| Refresh-Ahead | Normal | Zero Misses (Background refreshed) | Very Low | None |\n