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Re: postgres_fdw: wrong results with self join + enable_nestloop off

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: Nishant Sharma <nishant.sharma@enterprisedb.com>, Suraj Kharage <suraj.kharage@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2023-06-25T06:05:05Z
Lists: pgsql-hackers 
On Wed, Jun 14, 2023 at 2:49 PM Etsuro Fujita <etsuro.fujita@gmail.com>
wrote:

> On Mon, Jun 5, 2023 at 10:19 PM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
> > To avoid this issue, I am wondering if we should modify
> > add_paths_to_joinrel() in back branches so that it just disallows the
> > FDW to consider pushing down joins when the restrictlist has
> > pseudoconstant clauses.  Attached is a patch for that.
>
> I think that custom scans have the same issue, so I modified the patch
> further so that it also disallows custom-scan providers to consider
> join pushdown in add_paths_to_joinrel() if necessary.  Attached is a
> new version of the patch.


Good point.  The v2 patch looks good to me for back branches.

I'm wondering what the plan is for HEAD.  Should we also disallow
foreign/custom join pushdown in the case that there is any
pseudoconstant restriction clause, or instead still allow join pushdown
in that case?  If it is the latter, I think we can do something like my
patch upthread does.  But that patch needs to be revised to consider
custom scans, maybe by storing the restriction clauses also in
CustomPath?

Thanks
Richard

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Re-allow FDWs and custom scan providers to replace joins with pseudoconstant quals.

  2. Disallow replacing joins with scans in problematic cases.

  3. doc: PQinitOpenSSL and PQinitSSL are obsolete in OpenSSL 1.1.0+