Apart from maybe the last one, none of them are classical algo problems.
They're basic math problems.
Query takes N milliseconds which is too long, mainly consisting of z & c when I run my profiler. It does x * y = z of these things and a * b = c of these things.
As z is the biggest number, can I reduce x or y?
And even the last one you're better off actually trying out the technologies to trying to armchair theorize which tech is a better fit as without reading all their code you can't really see what they're really doing compared to what they say they do. Heroku being a pertinent case in point.
Unless you know "classical algorithms" and their typical performance characteristics, you are bound to waste time tweaking and may even rediscover a few complexity theorems, reductions and even complexity classes all on your own.
Oh you could just know the basics and classical algorithms and able to do a smell test of algorithmic performance.