Re: indxpath.c's references to IndexOptInfo.ncolumns are all wrong, no?

On Sun, Feb 10, 2019 at 5:18 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Apparently, whoever went through indxpath.c to substitute nkeycolumns
> for ncolumns was not paying attention. As far as I can tell, the
> *only* place in there where it's correct to reference ncolumns is in
> check_index_only, where we determine which columns can be extracted from
> an index-only scan.

Ugh. Yeah, it's rather inconsistent.

> I've got mixed feelings about whether to try to fix this before
> tomorrow's wraps. The attached patch seems correct and passes
> check-world, but there's sure not a lot of margin for error now.
> Thoughts?

I think that it should be fixed in the next point release if at all
possible. The bug is a simple omission. I have a hard time imagining
how your patch could possibly destabilize things, since nkeycolumns is
already used in numerous other places in indxpath.c.

--
Peter Geoghegan