Hi, On 2018-09-20 17:06:36 -0700, Mark Dilger wrote: > I should think that spilling anything to a tuplestore would only be needed > if the query contains an ORDER BY expression. If you query > > FETCH FIRST 50 PERCENT * FROM foo; > > you should just return every other row, discarding the rest, right? It's > only when an explicit ordering is given that the need to store the results > arises. Even with > > FETCH FIRST 50 PERCENT name FROM foo ORDER BY name; > > you can return one row for every two rows that you get back from the > sort node, reducing the maximum number you need to store at any time to > no more than 25% of all rows.
I'm doubtful about the validity of these optimizations, particularly around being surprising. But I think more importantly, we should focus on the basic implementation that's needed anyway. Greetings, Andres Freund
