When is it time to add more cores to your virtual server? [closed]

Your performance may have nothing to do with core-count. Yo could be I/O-constrained or just not have enough RAM on the system.

What are the specifications of the underlying system hardware? E.g. CPU model, clock speed, RAM amount.

Is the performance poor compared to another metric? Your expectations? Has the performance always been bad?

In general, I look at system load as the way to determine if the core count is sufficient. It sounds like it's at the right level in your situation.

The performance is poor, and I am pretty sure it's the DB queries that are slow.

If you are confident that is the issue, then have you optimized your MySQL or MSSQL install? Simply installing software without performance tuning will not be solved by just throwing more resources at it.

I recommend using the MySQL Tuning Primer Script located here. Very easy to use & the recommendations are pretty spot on.

Depending on your setup you might need to learn how to performance tune by hand—meaning you learn to interpret MySQL output yourself and act on it—but this script works quite well for 95% of the setups I have ever used them on. The other 5% are database idiosyncratic setups that required more custom care. I highly recommend tutorials like this one on the MySQL performance blog.