MongoDB connection pool size

[jim3692]

I was stress testing the app in a local server and I discovered that the responses are sent in batches of 5. After some research I found that mongoose uses its default connection pool size, which is 5 (documentation). However, MongoDB's native driver has a default of 100 connections (documentation).

I would recommend changing mongoose.connect call in app.js to:

mongoose.connect(config.MONGO[process.env.NODE_ENV], {
  connectTimeoutMS: 120000,
  socketTimeoutMS: 120000,
  poolSize: 100 // MongoDB's default
})

[apavlidi]

Hi @jim3692

Can you please provide your stress test technique/data sets and the results before/after the change? It would be very helpful for us to reproduce and verify your suggestion.

Thank you for your contribution

[jim3692]

The first test I run was inaccurate since I used Chrome and Firefox to run the test. However, both browsers have a limit of 6 parallel connections (as mr. @asidirop noted in a personal email). I run new tests on /announcements/public, which does not need authentication, using Apache Bench.

The results showed that, when the pool size is higher than the concurrency in Apache Bench, the API needs less time to respond to other requests that need access to the database.

We also tried to change this value in the production server and we saw an improvement when the server is stressed with an Apache Bench instance running in https://users.iee.ihu.gr.