I find it interesting, as recently I was reading about how complex it would/could be to create an index suggester.

https://www.depesz.com/2021/10/22/why-is-it-hard-to-automati...

I did something similar for a NoSQL database [1]. The biggest surprise was how much the query performance can change for an index when the data distribution changes slightly. For example using a real distribution for an 'age' field instead of just using a random number like in the test data.

[1] https://rxdb.info/query-optimizer.html

This sounds really cool!

I've sometimes wondered why server-based RDBMSs don't offer something like this. Is it too hard to implement? Or did people just not think of it? Or do they have something like this and I just never learned about it?

In Postgres land, hypopg:

https://github.com/HypoPG/hypopg