Re: improve DEBUG1 logging of parallel workers for CREATE INDEX?

From: Sami Imseih <samimseih(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Guillaume Lelarge <guillaume(at)lelarge(dot)info>, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: improve DEBUG1 logging of parallel workers for CREATE INDEX?
Date: 2025-01-19 05:40:32
Message-ID: CAA5RZ0tTpqUjNc3FcegjW9njZWSPSE0tFN9d4BCLh_c+whgZwA@mail.gmail.com
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> Hmm. I am reading Tom's opinion that goes toward not going in this
> direction for more commands, with the point to extend EXPLAIN to show
> this kind of information:
> https://www.postgresql.org/message-id/1692530.1736369905@sss.pgh.pa.us

That sounds like the ability to do something like EXPLAIN CREATE INDEX ...
is that correct?

> So do we really want to do what's proposed here? I'm +-0 about the
> VERBOSE option attached to more commands, as it is a bit harder for
> clients to catch the information wanted. So here comes my question:
> how do we want to consume this information at the end from the
> perspective of the client?

For interactive usage in psql or pgadmin, it's trivial to capture this
information. The
information can also be written to the server log with log_min_messages=INFO

A bit more work is required to redirect messages to an out file from psql, as
you need to ensure that stderr is redirected to a file.
It's also a bit more work to capture this information from something like a
JDBC application.

IMO the interactive use-case is where this is the most useful as you can start a
CREATE INDEX (VERBOSE) and ensure that it's going to launch all the parallel
workers that it planned before letting it it continue; or control-c and figure
out why not all planned workers launched.

Regards,

Sami

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