I came here to mention the exact same line: > if you want to build a really fast program What's meant here? Is "want to build" a requirement? And what does "r

I came here to mention the exact same line: > if you want to build a really fast program What's meant here? Is "want to build" a requirement? And what does "really fast mean? I'd say you need to look at this per project. Sometimes "fast enough" means you can store most things in an RDMS, sometimes it means you need Redis. Sometimes fast enough means you can use Ruby, sometimes it means you need C/C++/Rust. It's all trade offs. Having all data in RDBMS makes a lot of things easier (manage infra, manage local dev setups, transactions, joins, etc). Having Rails for web dev can get you from zero to wow pretty fast (lots of plugins, quick rebuilds, REPLs on errors, a console with db connectivity for trying the code yr about to add). These two can save a lot resources on development. But dont expect to out perform an app that uses Rust+Redis. Know your project, and know what is commonly picked to attack such a project. This is much better advise than "dont compromise on performance".