Saying "Premature optimization" is fine, as long as you leave yourself a way out. And the way out is clear here - when your database no longer can handle the lo

Saying "Premature optimization" is fine, as long as you leave yourself a way out. And the way out is clear here - when your database no longer can handle the load, drop the DB check constraints and move them over to application layer. Could you please elaborate on the "security" part of your comment? To me it seems database level checks would be more secure, as they would work with every possible way to update data, rather than just the blessed paths going through the app layer. And as far as scalability goes... it depends. If your ambition is to take on twitter, you probably need to take scaling seriously on every step along the way. However, I've been building mainly B2B systems for 15 years now, and just about all of them have been purring away happily on the low end of AWS RDS offerings. There are orders of magnitude more performance available at the click of a button. Database scalability is not something that keeps me up at night.