Re: Foreign Join pushdowns not working properly for outer joins

On 7 March 2017 at 01:22, Ashutosh Bapat
<ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> On Mon, Mar 6, 2017 at 1:29 PM, David Rowley
> <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> On 6 March 2017 at 18:51, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> On 2017/03/06 11:05, David Rowley wrote:
>> It seems like a much better idea to keep the server option processing
>> in one location, which is what I did.
>
> I agree with this. However
> 1. apply_server_options() is parsing the options strings again and
> again, which seems wastage of CPU cycles. It should probably pick up
> the options from one of the joining relations. Also, the patch calls
> GetForeignServer(), which is not needed; in foreign_join_ok(), it will
> copy it from the outer relation anyway.
> 2. Some server options like use_remote_estimate and fetch_size are
> overridden by corresponding table level options. For a join relation
> the values of these options are derived by some combination of
> table-level options.

This seems much more sane. I'd failed to find the code which takes the
largest fetch_size.

> I think we should write a separate function
> apply_fdw_options_for_joinrel() and pass the fpinfos of joinrel, outer
> and inner relation. The function will copy the values of server level
> options and derive values for table level options. We would add a note
> there to keep this function in sync with apply_*_options(). I don't
> think there's any better way to keep the options in sync for base
> relations and join relations.
>
> Here's the patch attached.

Agreed. It seems like a good idea to keep that logic in a single location

I've beaten your patch around a bit and come up with the attached.

The changes from yours are mostly cosmetic, but I've also added a
regression test too.

What do you think?

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services