Add a Write-Through Cache

A read-heavy user profile service (5:1 read/write ratio) is overloading the database. Add a write-through cache.

Context

Write-through caching updates both the cache and the database atomically on every write, keeping them permanently in sync. As a result, every read is served from cache with no risk of stale data — the database receives far fewer queries and read latency stays sub-millisecond even under write traffic. Use it for read-heavy workloads where stale reads are unacceptable; accept the trade-off that writes are slightly slower because each one must update two stores before returning.

Requirements

•Add a cache layer between the client and the database
•On every write, update both cache and DB atomically
•Serve all reads from the cache — no DB calls on a cache hit

Non-Functional Requirements

•Cache and DB must stay in sync — no stale reads after a write

Constraints

•Focus on the cache integration only — ignore auth, CDN, and monitoring

Evaluation Criteria

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