> What is the specific use case for this? This sounds quite general case.
They are both general cases in some sense, but the concerns lie mostly with what happens when they're unexpectedly encountered. For example, if the expected row count or group size is off by a good bit and we effectively have to perform a sort of all (or most) possible rows.
If we can get the performance to a point where that misestimated row count or group size doesn't much matter, then ISTM including the patch becomes a much more obvious total win.
I was trying to think of ways of using external information/circumstance to knowingly avoid negative use cases. i.e. don't treat sort as a black box, use its context.
