> Seems like a lotta work for a partial solution :-(. Probably the path
> of least resistance is to teach the planner that only some index AMs can
> do backwards scan. That would result in a Materialize buffer getting
> placed in front of the query if the user demanded scroll capability,
> but it would cost nothing in the more typical case where backwards scan
> isn't needed.
Probably, it will be a better solution. In this case GiST code could be
simplified - remove support of backward scan (in any case not fully workable)
>
> It should be sufficient to specify this in pg_am, right? Or could the
> opclass or indexkey details affect it?
I don't see any examples where it depends on opclass or index key, that's is a
AM property.
>
> BTW, can GIN do backwards scan?
No, at all.
--
Teodor Sigaev E-mail: teodor@sigaev.ru
WWW: http://www.sigaev.ru/