Severe performance issues

Issue Description

What are you doing?

Running a web server that does 1 SQL query and returns results:

const tag = await models.tag.findOne({
	where: {name: ctx.params.name},
});

What do you expect to happen?

3500+ req/s

What is actually happening?

460 req/s

Additional context

1. I tried patching the native Promise to add some extra functions that behave like Bluebird, and I was able to go up to ~830 req/s by ditching out Bluebird entirely.
2. I did a benchmark to my webserver with solely Redis query, it can do up to ~3500 req/s on a single CPU core.
3. I benchmarked mysql2, it can do up to 108,000 req/s - which is pretty much however fast is my running MariaDB server.

With that in mind, I believe sequelize does introduce extremely awkward procedures that bring the speed down to 430 req/s - note that it should ideally do 50,000+ queries/s assuming the webserver in front of it is ditched away.

Environment

• Sequelize version: 4.44.3
• Node.js version: 12.11.1
• Operating System: Arch Linux

Issue Template Checklist

How does this problem relate to dialects?

• I think this problem happens regardless of the dialect.
• I think this problem happens only for the following dialect(s):
• I don’t know, I was using PUT-YOUR-DIALECT-HERE, with connector library version XXX and database version XXX

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don’t know how to start, I would need guidance.
• No, I don’t have the time, although I believe I could do it if I had the time…
• No, I don’t have the time and I wouldn’t even know how to start.

[SimonSchick]

Sorry, already done https://github.com/sequelize/sequelize/pull/12167

[sushantdhiman]

@jedwards1211 is working on tests (converting them to async) @kroleg you can help us with documentation cleanup 😃