Dr. Ayush Bisht

Yes — setting `minPoolSize: 0` in MongoDB/Mongoose can affect speed, but mostly in specific situations.

### What `minPoolSize` does

`minPoolSize` defines the **minimum number of connections MongoDB keeps open** in the connection pool.

Example:

```js mongoose.connect(uri, { maxPoolSize: 20, minPoolSize: 0 }) ```

With `minPoolSize: 0`:

* No idle connections are kept alive unnecessarily * Connections can close when not being used * New requests may need to reopen connections later

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# Speed Impact

## ✅ Pros of `minPoolSize: 0`

### Better for:

* Serverless apps (like Vercel functions) * Low traffic apps * Saving memory/resources * Preventing too many idle DB connections

### Result:

Lower resource usage.

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## ❌ Cons

### Can increase latency on:

* First request after inactivity * Burst traffic after idle periods

Because MongoDB may need to:

1. Create new socket connections 2. Authenticate again 3. Warm up TLS/DNS

That can add:

* ~20ms–200ms extra latency * Sometimes more on cold starts

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# In High Traffic Apps

If your app gets continuous traffic:

* `minPoolSize: 0` usually has very little negative effect * Pool stays naturally warm because requests keep connections active

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# Recommended Usage

## For Next.js + MongoDB Atlas

Usually good:

```js maxPoolSize: 20, minPoolSize: 0 ```

Especially if:

* You cache the mongoose connection globally * You're on serverless * Traffic is moderate

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## For very high-performance APIs

You might use:

```js minPoolSize: 5 ```

This keeps some connections always ready and reduces cold latency.

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# Important Thing

`minPoolSize` is usually NOT the reason for major slowness.

Much bigger performance factors are:

* Missing DB indexes * `.populate()` overuse * No `.lean()` * Large payloads * SSR hitting DB every request * N+1 queries * Bad aggregation pipelines * No caching

Those affect performance far more than `minPoolSize`.