Yes, all of those databases allocate query memory for queries at connection time, and consequently don't scale efficiently for large number of idle clients. Tha

Yes, all of those databases allocate query memory for queries at connection time, and consequently don't scale efficiently for large number of idle clients. That's not all databases. Some don't do that. Some don't even do connections period. Connection pools are a necessary work around for a specific design decision with the system software. They can be helpful other problems as well, but they aren't necessarily a requirement.