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References: <19473-92f01422b9220412@postgresql.org>
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From: Fujii Masao <masao.fujii@gmail.com>
Date: Tue, 12 May 2026 22:47:24 +0900
Message-ID: 
 <CAHGQGwGnPPLL_yEnkeYfbQ5waCAdF3i3TLD0PODeJFGgYb8WRg@mail.gmail.com>
Subject: Re: BUG #19473: regression error in dblink: another command is
 already in progress
To: o15611@gmail.com, pgsql-bugs@lists.postgresql.org
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On Sat, May 9, 2026 at 4:43=E2=80=AFAM PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference:      19473
> Logged by:          Oleg Ivanov
> Email address:      o15611@gmail.com
> PostgreSQL version: 18.3
> Operating system:   Linux
> Description:
>
> Testcase:
> SELECT * FROM dblink('dbname=3Dpostgres user=3Dpostgres', $$ select 7; $$=
 ) as
> (col1 int);
> SELECT * FROM dblink_connect('connection1', 'host=3D/var/run/postgresql
> port=3D5432');
> SELECT * FROM dblink_send_query('connection1', $$ select 8 from pg_sleep(=
1);
> $$ );
> SELECT dblink_is_busy('connection1');
> SELECT * FROM dblink_get_result('connection1') as t(col1 int);
> --- SELECT dblink_is_busy('connection1');
> SELECT * FROM dblink_exec('connection1', $$ CHECKPOINT; $$);
> SELECT * FROM dblink_disconnect('connection1');
>
>  col1
> ------
>     7
> (1 row)
>
>  dblink_connect
> ----------------
>  OK
> (1 row)
>
>  dblink_send_query
> -------------------
>                  1
> (1 row)
>
>  dblink_is_busy
> ----------------
>               1
> (1 row)
>
>  col1
> ------
>     8
> (1 row)
>
> ERROR:  another command is already in progress
> CONTEXT:  while executing command on dblink connection named "connection1=
"
>  dblink_disconnect
> -------------------
>  OK
> (1 row)
>
> There was no error in 16 version. The error appeared in 17 version. It
> seems, there is a regression bug.
> The workaround is to uncomment a commented statement.

The documentation for dblink_get_result() notes "It must be called once for
each query sent, and one additional time to obtain an empty set result,
before the connection can be used again". So in your case, it seems that
dblink_get_result() needs to be called one more time before calling
dblink_exec(). If you do that, I think that the error "another command is
already in progress" should not occur. Therefore, this does not seem to be
a bug to me. Thought?

Regards,

--=20
Fujii Masao