How do I share a MongoDB connection across requests in Next.js?

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How do I share a MongoDB connection across requests in Next.js?

asked 1 month ago

427

I keep hitting connection-pool exhaustion in development. Every time I save a file, a new Mongoose connection seems to be created.

1import mongoose from "mongoose"
2
3export async function connect() {
4  return mongoose.connect(process.env.MONGODB_URI!)
5}

1import mongoose from "mongoose"
2
3export async function connect() {
4  return mongoose.connect(process.env.MONGODB_URI!)
5}

In production this looks fine, but locally the connection count climbs until Atlas starts refusing new ones. What is the accepted pattern here?

nextjs

mongodb

nodejs

2 Answers

Ada Sharma

• answered 1 month ago

The problem is hot reloading. Next.js re-evaluates the module on every save, so the module-level state is thrown away and a fresh connection is opened.

Cache the connection on globalThis, which survives module reloads:

1let cached = global.mongoose
2
3if (!cached) {
4  cached = global.mongoose = { conn: null, promise: null }
5}
6
7export async function dbConnect() {
8  if (cached.conn) return cached.conn
9
10  if (!cached.promise) {
11    cached.promise = mongoose.connect(process.env.MONGODB_URI!, {
12      dbName: "devflow",
13    })
14  }
15
16  cached.conn = await cached.promise
17  return cached.conn
18}

1let cached = global.mongoose
2
3if (!cached) {
4  cached = global.mongoose = { conn: null, promise: null }
5}
6
7export async function dbConnect() {
8  if (cached.conn) return cached.conn
9
10  if (!cached.promise) {
11    cached.promise = mongoose.connect(process.env.MONGODB_URI!, {
12      dbName: "devflow",
13    })
14  }
15
16  cached.conn = await cached.promise
17  return cached.conn
18}

Caching the promise as well as the connection matters — without it, concurrent requests during a cold start each kick off their own connect().

Tomas Novak

• answered 1 month ago

Adding to the above: set maxPoolSize explicitly. The driver default of 100 is far more than a serverless function needs, and on Atlas free tiers you will hit the cluster limit long before you hit the pool limit.

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How do I share a MongoDB connection across requests in Next.js?

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