Re: How and at what stage to stop FDW to generate plan with JOIN.

On Wed, Apr 24, 2019 at 1:15 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com> writes:
> > I am working on an FDW where the database does not support any operator
> > other than "=" in JOIN condition. Some queries are genrating the plan
> with
> > JOIN having "<" operator. How and at what stage I can stop FDW to not
> make
> > such a plan. Here is my sample query.
>
> What exactly do you think should happen instead? You can't just tell
> users not to ask such a query. (Well, you can try, but they'll probably
> go looking for a less broken FDW.)
>
> I know that.

> If what you really mean is you don't want to generate pushed-down
> foreign join paths containing non-equality conditions, the answer is
> to just not do that. That'd be the FDW's own fault, not that of
> the core planner, if it creates a path representing a join it
> can't actually implement. You'll end up running the join locally,
> which might not be great, but if you have no other alternative
> then that's what you gotta do.
>
> Yes, that's what I am thinking. In case of non-equality condition join
them locally is
the only solution. I was just confirming.

> If what you mean is you don't know how to inspect the join quals
> to see if you can implement them, take a look at postgres_fdw
> to see how it handles the same issue.
>
> I really don't know postgres_fdw have the same issue, but yes postgres_fdw
is always my starting point.

> regards, tom lane
>

--
Ibrar Ahmed