Re: Super PathKeys (Allowing sort order through precision loss functions)

Robert Haas <robertmhaas@gmail.com> writes:
> This kinda reminds me of commit
> 8f9fe6edce358f7904e0db119416b4d1080a83aa.  We needed a way to provide
> the planner with knowledge about the behavior of specific functions.
> In that case, the specific need was to be able to tell the planner
> that a certain function call could be omitted or strength-reduced, and
> we did that by having the planner call a function that encoded the
> necessary knowledge.  Here, we want to evaluate a function call and
> see whether it is order preserving, which could depend on a whole
> bunch of stuff that isn't easily parameterized by catalog entries, but
> could be figured out by a C function written for that purpose.

+1.  If we're otherwise going to need multiple pg_proc columns, this
is a better answer just from the standpoint of avoiding pg_proc bloat:
we'd only need to add one OID column.  And I concur with your point
that we're going to have a really hard time parameterizing the mechanism
adequately if there isn't dedicated per-function code.

            regards, tom lane