On Fri, Jul 8, 2022 at 12:30 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > Ibrar Ahmed <ibrar.ah...@gmail.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 > Hi, In createplan.c, there is `change_plan_targetlist`
Plan * change_plan_targetlist(Plan *subplan, List *tlist, bool tlist_parallel_safe) But it doesn't have `Path` as parameter. So I am not sure whether the check of non-returnable columns should be done in change_plan_targetlist(). bq. for example with columnar storage or FDWs, Yeah. The above is the case where I want to optimize. Cheers
