Re: Aggregate leads to superfluous projection from the scan

Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com> writes:
> I give a quick look and I think in case whenever data is extracted from the
> heap it shows all the columns. Therefore when columns are extracted from
> the index only it shows the indexed column only.

This is operating as designed, and I don't think that the proposed
patch is an improvement. The point of use_physical_tlist() is that
returning all the columns is cheaper because it avoids a projection
step. That's true for any case where we have to fetch the heap
tuple, so IndexScan is included though IndexOnlyScan is not.

Now, that's something that was true a decade or more ago.
There's been considerable discussion recently about cases where
it's not true anymore, for example with columnar storage or FDWs,
and so we ought to invent a way to prevent createplan.c from
doing it when it would be counterproductive. But just summarily
turning it off is not an improvement.

regards, tom lane