[antonchekhov]

It's been many years since I've had to use an Oracle db, but they definitely allowed SQL developers to forcibly specify a query-plan - called "query hints", wherein you could specify it to prefer using (or avoiding) certain indexes, certain join-strategies (hash, loop, etc) - this was done via comments immediately before the SQL query - see https://docs.oracle.com/cd/B13789_01/server.101/b10752/hints...

Postgresql doesn't have this, however, I've rarely missed this feature - tables with good indexes, regular db hygiene, etc, almost always perform excellently. The query planner is very, very smart nowadays.

[aldonius]

The query hints thing is actually quite useful in an educational context.

There's DB internals/performance course which I'm a TA for and we lean heavily on being able to force Oracle's rule-based or cost-based optimisers --- because then we can get the students to analyse and compare the plans.