Date: Mon, 19 Apr 2021 19:16:37 -0400
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Robert Haas <robertmhaas@gmail.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: when the startup process doesn't
Message-ID: <20210419231637.GA24815@alvherre.pgsql>
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On 2021-Apr-19, Robert Haas wrote:

> Another possible approach would be to accept connections for
> monitoring purposes even during crash recovery. We can't allow access
> to any database at that point, since the system might not be
> consistent, but we could allow something like a replication connection
> (the non-database-associated variant).

Hmm.  We already have pg_isready, which is pretty simplistic -- it tries
to connect to the server and derive a status in a very simplistic way.
Can we perhaps improve on that?  I think your idea of using the
non-database-connected replication mode would let the server return a
tuple with some status information with a new command.  And then
pg_isready could interpret that, or just print it.

-- 
Álvaro Herrera                            39°49'30"S 73°17'W
Subversion to GIT: the shortest path to happiness I've ever heard of
                                                (Alexey Klyukin)