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From: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Date: Fri, 7 Mar 2025 09:08:51 +0100
Message-ID: 
 <CAO6_XqpTYH0MsYGqPG4Y0pQdNdrdXVO-K_1zws-LfN9wtWUTPQ@mail.gmail.com>
Subject: Re: Add Pipelining support in psql
To: Jelte Fennema-Nio <postgres@jeltef.nl>
Cc: Michael Paquier <michael@paquier.xyz>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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On Thu, Mar 6, 2025 at 5:20=E2=80=AFAM Michael Paquier <michael@paquier.xyz=
> wrote:
> That was not a test case we had in mind originally here, but if it is
> possible to keep the implementation simple while supporting your
> demand, well, let's do it.  If it's not that straight-forward, let's
> use the new meta-command, forbidding \g and \gx based on your
> arguments from upthread.

I think the new meta-command is a separate issue from allowing ';' to
push in a pipeline. Any time there's a change or an additional format
option added to \g, it will need to be forbidden for pipelining. The
\sendpipeline meta-command will help keep those exceptions low since
the whole \g will be forbidden.

Another possible option would be to allow both \g and \gx, but send a
warning like "printing options within a pipeline will be ignored" if
those options are used, similar to "SET LOCAL" warning when done
outside of a transaction block. That would have the benefit of making
existing scripts using \g and \gx compatible.

For using ';' to push commands in a pipeline, I think it should be
fairly straightforward. I can try to work on that next week (I'm
currently chasing a weird memory context bug that I need to finish
first).

On Fri, Mar 7, 2025 at 1:05=E2=80=AFAM Jelte Fennema-Nio <postgres@jeltef.n=
l> wrote:
> One thing I've noticed is that \startpipeline throws warnings when
> copy pasting multiple lines. It seems to still execute everything as
> expected though. As an example you can copy paste this tiny script:
>
> \startpipeline
> select pg_sleep(5) \bind \g
> \endpipeline
>
> And then it will show these "extra argument ... ignored" warnings
>
> \startpipeline: extra argument "select" ignored
> \startpipeline: extra argument "pg_sleep(5)" ignored

It looks like an issue with libreadline. At least, I've been able to
reproduce the warnings and 'readline(prompt);' returns everything as a
single line, with the \n inside the string. This explains why what is
after \startpipeline is processed as arguments. This can also be done
with:
select 1 \bind \g
select 2 \bind \g
And somehow, I couldn't reproduce the issue anymore once I've compiled
and installed libreadline with debug symbols.