Mongoose Connection Pool

Question

I noticed in the Mongoose docs that there is support for a connection pool.

http://mongoosejs.com/docs/connections.html

Considering that node is single threaded why is there a connection pool? What's the lifecycle of connections in the pool?

Answer 1

Connection pools don't have anything to do with async vs sync -- it just works like so:

• You can specify an amount of open connections to maintain to your database (let's say 10).
• Each time your Node JS code makes a query, if possible, it'll use one of the already-open 10 connections to make this request -- this way you can avoid the overhead of opening a new database connection for each query.

Maintaining a connection pool is essentially maintaining an array of db connection objects, and picking unused ones for every query. It's not actually effecting threads or processes at all =)

Answer 2

apparently node is a single threaded but internally when node makes a call to IO operation under the hood it has some threading mechanism through which it performs IO. Main thread doesn't perform this IO operation itself, if it was performing IO, system would be dead already.

https://codeburst.io/how-node-js-single-thread-mechanism-work-understanding-event-loop-in-nodejs-230f7440b0ea