Re: Tid scan improvements

Edmund Horner <ejrh00(at)gmail(dot)com> writes:
> Ok. I think that will simplify things. So if I follow you correctly,
> we should do:

> 1. If has_useful_pathkeys is true: generate pathkeys (for CTID ASC),
> and use truncate_useless_pathkeys on them.
> 2. If we have tid quals or pathkeys, emit a TID scan path.

Check.

> For the (optional) backwards scan support patch, should we separately
> emit another path, in the reverse direction?

What indxpath.c does is, if has_useful_pathkeys is true, to generate
pathkeys both ways and then build paths if the pathkeys get past
truncate_useless_pathkeys. That seems sufficient in this case too.
There are various heuristics about whether it's really useful to
consider both sort directions, but that intelligence is already
built into truncate_useless_pathkeys. tid quals with no pathkeys
would be reason to generate a forward path, but not reason to
generate a reverse path, because then that would be duplicative.

regards, tom lane