Re: Push down more full joins in postgres_fdw

>
>
> Ashutosh proposed this to do the comparison:
>
> On 2016/11/22 18:28, Ashutosh Bapat wrote:
>>
>> I guess, the reason why you are doing it this way, is SELECT clause for
>> the
>> outermost query gets deparsed before FROM clause. For later we call
>> deparseRangeTblRef(), which builds the tlist. So, while deparsing SELECT
>> clause, we do not have tlist to build from. In that case, I guess, we have
>> to
>> build the tlist in get_subselect_alias_id() if it's not available and
>> stick it
>> in fpinfo. Subsequent calls to get_subselect_alias_id() should find tlist
>> there. Then in deparseRangeTblRef() assert that there's a tlist in fpinfo
>> and use it to build the SELECT clause of subquery. That way, we don't
>> build
>> tlist unless it's needed and also use the same tlist for all searches.
>> Please
>> use tlist_member() to search into the tlist.
>
>
> This would probably work, but seems to me a bit complicated. Instead, I'd
> like to propose that we build the tlist for each relation being deparsed as
> a subquery in a given join tree, right before deparsing the SELECT clause in
> deparseSelectStmtForRel, if is_subquery is false and lower_subquery_rels
> isn't NULL, and store the tlist into the relation's fpinfo. That would
> allow us to build the tlist only when we need it, and to use tlist_member
> for the exact comparison. I think it would be much easier to implement
> that.
>

IIRC, this is inline with my original proposal of creating tlists
before deparsing anything. Along-with that I also proposed to bubble
this array of tlist up the join hierarchy to avoid recursion [1] point
#15, further elaborated in [2]

[1] https://www.postgresql.org/message-id/ad449b25-66ee-4c06-568c-0eb2e1bef9f9%40lab.ntt.co.jp
[2] https://www.postgresql.org/message-id/CAFjFpRcn7%3DDNOXm-PJ_jVDqAmghKVf6tApQC%2B_RgMZ8tOPExcA%40mail.gmail.com

We seem to be moving towards that solution, but as discussed we have
left it to committer's judgement.
--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company