Subject: d844cd75a and postgres_fdw

From: Devrim Gündüz <[email-masked]>
Date: Tue, 24 Oct 2023 12:46:40 +0100

Hi,

I'm seeing an issue after upgrading from 12.13 to 15.4. This happens
when we run a query against a foreign table (fdw on the same instance to
a different database) -- but does not appear when we get rid of
postgres_fdw:

ERROR:  cursor can only scan forward
HINT:  Declare it with SCROLL option to enable backward scan.
CONTEXT:  remote SQL command: MOVE BACKWARD ALL IN c1

SQL state: 55000

I attached the query. The name of the foreign table is
"foobar.sys_user".

Looks like the bug #17889, and this is the last email in that thread: 
https://www.postgresql.org/message-id/1852635.1682808624%40sss.pgh.pa.us

OTOH, same query works (against the FDW) when we remove the following
WHERE clause:

WHERE
    tbl.table_status = 'A'
    AND tbl.table_id <> 1
    AND tbl.table_id <> - 2

Any hints?

Regards,

-- 
Devrim Gündüz
Open Source Solution Architect, PostgreSQL Major Contributor
Twitter: @DevrimGunduz , @DevrimGunduzTR

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From: Etsuro Fujita <[email-masked]>
Date: Fri, 5 Jul 2024 21:56:28 +0900

> OTOH, same query works (against the FDW) when we remove the following

The error occurs when rescanning a postgres_fdw foreign relation, so I
think the reason why the query works would be that the planner chose a
join plan other than a nestloop join plan.

I proposed a fix for this in [1].

Best regards,
Etsuro Fujita

[1] https://www.postgresql.org/message-id/CAPmGK149UubRQGLH6QaBkhJvas%2BGz%2BT6tx2MBX9MTJpxDRKPBA%40mail.gmail.com

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From: Etsuro Fujita <[email-masked]>
Date: Fri, 19 Jul 2024 14:01:54 +0900

> I proposed a fix for this in [1].

I pushed the fix and back-patched to v15.  Thanks for the report!

Best regards,
Etsuro Fujita

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From: Devrim Gündüz <[email-masked]>
Date: Fri, 19 Jul 2024 14:29:41 +0300

Hi,

> I pushed the fix and back-patched to v15.  Thanks for the report!

Thanks a lot!

Regards,