Use Dedicated CPU or High memory plan for production DB?

While there’s not a difference in disk IO between plans, since database applications are usually more memory intensive, a High Memory plan might be the way to go. Another thing to consider is that since database intensive servers read/write a lot of data, you may require more disk space than the Dedicated plans provide.

You also might be okay with using a Standard plan that provides a decent combination of RAM and disk space. Though this all depends on your use case. If you started with a Standard plan and monitored your CPU and memory usage, as well as your disk space, you could decide which direction you needed to go from there in terms of your plan size.

Thanks.

Disk space is not a matter for me, what I concern about is the average performance.

My understanding is there are fewer VM ratio on Dedicated CPU Plans than Standard/High Memory Plans, so the chance of having noisy neighbours who eaten my disk I/O also reduced. Is that correct?

From what I understand there isn't a difference regarding the ratio for Dedicated vs. Standard/High Memory Plans. If you were primarily concerned about CPU steal, then a Dedicated Plan would be ideal. As for I/O steal, it's very rare that we see this. So if this is your primary concern, then either the Standard or High Memory Plans should work just fine for you :)