express-dedupe

Zero-config Express middleware for request deduplication — merges identical concurrent HTTP requests into a single database call, preventing cache stampedes, thundering herd problems, and race conditions in Node.js applications.

express-dedupe

Your database is getting hit 500 times for the same request. Here's why that's killing your app.

When 500 users load the same page at the same time, your server fires 500 identical database queries — all at once. Your database chokes. Your app slows down. Users see errors.

This is called a cache stampede. It's common. It's silent. And it crashes real apps.

express-dedupe fixes this with 2 lines of code.

It intercepts duplicate requests and merges them into one. Instead of 500 DB queries, only 1 runs. Every user still gets their response — instantly.

npm install express-dedupe

import { dedupe } from 'express-dedupe'

app.use(dedupe()) // done. your routes need zero changes.

No config. No rewrites. Works with any database.

Performance

| Scenario | Without Package | With Package | |-------------------------------|-------------------|-----------------| | 500 users, Redis HIT | 500 Redis reads | 500 Redis reads | | 500 users, Redis MISS | 500 DB queries | 1 DB query | | 500 users, no cache | 500 DB queries | 1 DB query | | HashMap lookup | — | O(1) | | Memory per in-flight entry | — | 1 Promise ref | | Memory when idle | — | 0 |

FAQ

Does it work without Redis? Yes. Redis is completely optional. express-dedupe works on any Express backend regardless of caching layer.

Does it work with MongoDB, PostgreSQL, MySQL, or any ORM? Yes. The middleware operates at the HTTP request layer and has no knowledge of — or dependency on — which database or ORM sits underneath.

What if the database query throws an error? The error is propagated to all waiting requests. Every user attached to that in-flight Promise receives the same error response. The HashMap entry is cleared immediately so the next request starts fresh.

Is it safe for POST requests? No. POST is a write operation and each call must reach the database independently. express-dedupe applies to GET and HEAD by default. Never add POST to methods.

Does it work with Node.js clusters or horizontal scaling? Each process maintains its own in-flight HashMap. Deduplication is scoped to a single process. For cluster-wide deduplication across multiple instances use a Redis-based distributed lock.

How is this different from Redis caching? Redis stores query results for minutes or hours. express-dedupe merges requests that arrive within the same millisecond window before a result exists. They target different time scales and are designed to complement each other — not compete.

Can I use it with TypeScript? Yes. The package ships with full TypeScript definitions. All options, types, and the UrlPatternTrie class are fully typed and exported.