Re: postgres_fdw bug in 9.6

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: David Steele <david(at)pgmasters(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: postgres_fdw bug in 9.6
Date: 2017-03-31 12:50:57
Message-ID: b00c8024-b4f3-470b-f911-22a9c81d71ac@lab.ntt.co.jp
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On 2017/03/30 20:16, Ashutosh Bapat wrote:
> The patch applies cleanly, compiles. make check in regress as well as
> postgres_fdw works fine. Here are few comments

Thanks for the review!

> local-join should be local join.

OK, done.

> The comments should explain why.
> + /* Should be unparameterized */
> + Assert(outer_path->param_info == NULL);
> + Assert(inner_path->param_info == NULL);

Done.

> + a suitable local join path, which can be used as the alternative local
> May be we should reword this as ... which can be used to create an alternative
> local ... This rewording is required even in the existing docs.

Done.

> + /* outer_path should not require rels from inner_path */
> + Assert(!PATH_PARAM_BY_REL(outer_path, inner_path->parent));
> Probably this should throw an error or return NULL in such case rather than
> Asserting. This function is callable from any FDW, and that FDW may provide
> such paths, may be because of an internal bug. Same case with
> + /* Neither path should require rels from the other path */
> + Assert(!PATH_PARAM_BY_REL(outer_path, inner_path->parent) ||
> + !PATH_PARAM_BY_REL(inner_path, outer_path->parent));

Good idea! I think it's better to throw an error because that is a bug
in the FDW; done that way.

> While the comment below mentions ON true, the testcase you have added is for ON
> false. Either the testcase should change or this comment. That raises another
> question, what happens when somebody does FULL JOIN ON false?
> + * If special case: for "x FULL JOIN y ON true", there

FULL JOIN ON FALSE would be handled the same way as FULL JOIN ON TRUE,
so I think we should rewrite that comment into something like this: If
special case: for "x FULL JOIN y ON true" or "x FULL JOIN y ON false"...

> Why JOIN_RIGHT is being treated differently from JOIN_LEFT? We should be able
> to create a nested loop join for JOIN_RIGHT?
> + case JOIN_RIGHT:
> + case JOIN_FULL:

I don't think so, because nestloop joins aren't supported for
JOIN_RIGHT. See ExecInitNestLoop().

Best regards,
Etsuro Fujita

Attachment Content-Type Size
epqpath-for-foreignjoin-7.patch text/x-patch 46.1 KB

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