Subject: Re: BUG #17344: Assert failed on queiring async_capable foreign table
 with inheritance
To: Etsuro Fujita <etsuro.fujita@gmail.com>,
 Dmitry Dolgov <9erthalion6@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org
References: <17344-226b78b00de73a7e@postgresql.org>
 <20211225232625.5xuplnlegneh42cw@erthalion.local>
 <CAPmGK15F_oKapcDmrBeRD5bOiyTPhN+8UPPz6r0ANKwGei3hsQ@mail.gmail.com>
 <CAPmGK16n1VHbJHTRdrJ3vS8ZEv2vkFsNT_mf00kKffS04uctMw@mail.gmail.com>
From: Alexander Lakhin <exclusion@gmail.com>
Message-ID: <d10cbf5d-d45a-d3b4-51b3-0a80f5039ed3@gmail.com>
Date: Sun, 2 Jan 2022 22:00:00 +0300
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Hello Etsuro-san,
31.12.2021 10:36, Etsuro Fujita wrote:
> On Tue, Dec 28, 2021 at 10:14 PM Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
>> The root cause of the
>> assertion failure in the first case might be something other than the
>> limitation.  I’ll look into this in more detail.
> To fix, I modified postgresReScanForeignScan() so that we always
> process a pending async request (if any) before restarting the foreign
> scan.  Attached is a patch for that.  I tested the patch with the
> first case, and it addresses the assertion failure.
Thanks for the fix! I can confirm that it eliminates the failure and
propose a simple test case for the issue. Maybe you will find it useful.

Best regards,
Alexander

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diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index ee9ab37d56..9cc13475f6 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1935,6 +1935,15 @@ explain (verbose, costs off)
 select * from bar where f1 in (select f1 from foo) for share;
 select * from bar where f1 in (select f1 from foo) for share;
 
+-- Check asynchronous fetch with inheritance
+alter server loopback options (add async_capable 'true');
+create foreign table foo3 (f3 int)
+  server loopback options (table_name 'loct1');
+create foreign table bar3 () inherits(foo3)
+  server loopback options (table_name 'loct2');
+select f1 from foo where f1 in (select f1 from foo3);
+alter server loopback options (drop async_capable);
+
 -- Now check SELECT FOR UPDATE/SHARE with an inherited source table,
 -- where the parent is itself a foreign table
 create table loct4 (f1 int, f2 int, f3 int);

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