Re: Push down more full joins in postgres_fdw

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Push down more full joins in postgres_fdw
Date: 2016-10-27 07:16:41
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On 2016/10/26 19:53, Ashutosh Bapat wrote:
> On Wed, Oct 26, 2016 at 3:35 PM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:

>> In practice, the search cost would be negligible compared to the cost of
>> explaining/executing the query.
>> My concern about your proposal is: it might not be worth complicating the
>> code to solve a problem that is actually not a problem in practice.

> To me the current code looks complicated esp. because of the recursion
> involved and usage of out parameters to isSubqueryExpr().

I don't think so. isSubqueryExpr is prety small, written in less than
50 lines, and the code looks rather simple to me.

> My
> suggestion goes inline with the current method of deparsing a Var.

Yeah, I think your approach makes it easy to search for the alias to a
given Var from the array you proposed. I think the complexity of your
approach would be in extra work for building and maintaining the array
while deparsing the query. I think that would probably need more
invasive and much larger changes to the existing code than what I proposed.

I think this issue is optional, so I'd like to propose to leave this for
the committer's judge.

Best regards,
Etsuro Fujita

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