Cursor rule

1---
2alwaysApply: false
3---
4 
5## Cross-Request LRU Caching
6 
7`React.cache()` only works within one request. For data shared across sequential requests (user clicks button A then button B), use an LRU cache.
8 
9**Implementation:**
10 
11```typescript
12import { LRUCache } from 'lru-cache'
13 
14const cache = new LRUCache<string, any>({
15  max: 1000,
16  ttl: 5 * 60 * 1000  // 5 minutes
17})
18 
19export async function getUser(id: string) {
20  const cached = cache.get(id)
21  if (cached) return cached
22 
23  const user = await db.user.findUnique({ where: { id } })
24  cache.set(id, user)
25  return user
26}
27 
28// Request 1: DB query, result cached
29// Request 2: cache hit, no DB query
30```
31 
32Use when sequential user actions hit multiple endpoints needing the same data within seconds.
33 
34**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.
35 
36**In traditional serverless:** Each invocation runs in isolation, so consider Redis for cross-process caching.
37 
38Reference: [https://github.com/isaacs/node-lru-cache](https://github.com/isaacs/node-lru-cache)
39