Server Cache Lru

---
name: server-cache-lru
description: Cross-Request LRU Caching. Use when you need help with server cache lru.
license: CC-BY-NC-SA-4.0
metadata:
  risk: unknown
  source: community
  kind: mode
  category: rules
---

## Cross-Request LRU Caching

`React.cache()` only works within one request. For data shared across sequential requests (user clicks button A then button B), use an LRU cache.

**Implementation:**

```typescript
import { LRUCache } from "lru-cache";

const cache = new LRUCache<string, any>({
  max: 1000,
  ttl: 5 * 60 * 1000, // 5 minutes
});

export async function getUser(id: string) {
  const cached = cache.get(id);
  if (cached) return cached;

  const user = await db.user.findUnique({ where: { id } });
  cache.set(id, user);
  return user;
}

// Request 1: DB query, result cached
// Request 2: cache hit, no DB query
```

Use when sequential user actions hit multiple endpoints needing the same data within seconds.

**With Vercel's [Fluid Compute](https://vercel.com/docs/fluid-compute):** LRU caching is especially effective because multiple concurrent requests can share the same function instance and cache. This means the cache persists across requests without needing external storage like Redis.

**In traditional serverless:** Each invocation runs in isolation, so consider Redis for cross-process caching.

Reference: [https://github.com/isaacs/node-lru-cache](https://github.com/isaacs/node-lru-cache)