i agree that oracle was a solid choice 30 years ago, though they were already notorious for taking advantage of their customers
also postgres's query optimizer has gotten a lot better
i wouldn't say any open source database. it depends on your index. there are recondite but not unreasonable queries for which mariadb and sqlite still produce pathologically poor query plans which won't complete in a reasonable time even with all the data in ram. and a few years ago i had postgres totally fall over on important queries because we'd forgotten to add an index, and it took us days to figure it out because we were using amazon's outsourced postgres thing and didn't know how to admin it
also postgres's query optimizer has gotten a lot better
i wouldn't say any open source database. it depends on your index. there are recondite but not unreasonable queries for which mariadb and sqlite still produce pathologically poor query plans which won't complete in a reasonable time even with all the data in ram. and a few years ago i had postgres totally fall over on important queries because we'd forgotten to add an index, and it took us days to figure it out because we were using amazon's outsourced postgres thing and didn't know how to admin it