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

Etsuro Fujita <etsuro.fujita@gmail.com>

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From: Etsuro Fujita <etsuro.fujita@gmail.com>
To: Nishant Sharma <nishant.sharma@enterprisedb.com>
Cc: Richard Guo <guofenglinux@gmail.com>, Suraj Kharage <suraj.kharage@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2023-06-08T10:36:48Z
Lists: pgsql-hackers 
Hi,

On Wed, Jun 7, 2023 at 7:28 PM Nishant Sharma
<nishant.sharma@enterprisedb.com> wrote:
> Etsuro's patch is also showing the correct output for "set enable_nestloop=off". Looks good to me for back branches due to backport issues.
>
> But below are a few observations for the same:-
> 1) I looked into the query plan for both "set enable_nestloop" on & off case and observe that they are the same. That is, what we see with "set enable_nestloop=on".
> 2) In back branches for "set enable_nestloop" on & off value, at least this type of query execution won't make any difference. No comparison of plans to be selected based on total cost of two plans old (Nested Loop with Foreign Scans) & new (Only Foreign Scan) will be done, because we are avoiding the call to "postgresGetForeignJoinPaths()" up front when we have pseudo constants.

Thanks for looking!

Best regards,
Etsuro Fujita

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+