Horton

Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions

Stephen Frost <sfrost@snowman.net>

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From: Stephen Frost <sfrost@snowman.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Ian Barwick <ian.barwick@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-06-24T19:20:14Z
Lists: pgsql-hackers 
Greetings,

* Tom Lane (tgl@sss.pgh.pa.us) wrote:
> Stephen Frost <sfrost@snowman.net> writes:
> > Stephen and Magnus want a warning, because it's an indication that a
> > tool author, or *something* modified the file in an unexpected way, and
> > that we are having to do some kind of cleanup on the file because of it.
> 
> But you're presuming something that not everybody agrees with, which
> is that this situation should be considered unexpected.

And, at least at present, not everyone seems to be agreeing that having
duplicates should be considered expected, either.  Using only ALTER
SYSTEM, you'd never end up with duplicates either.

> In particular, in order to consider it unexpected, you have to suppose
> that the content rules for postgresql.auto.conf are different from those
> for postgresql.conf (wherein we clearly allow last-one-wins).  Can you
> point to any user-facing documentation that says that?

The backend and frontend tools don't modify postgresql.conf, and we
don't document how to modify postgresql.auto.conf at *all*, even though
we clearly now expect tool authors to go modifying it so that they can
provide the same capabilities that pg_basebackup does and which they
used to through recovery.conf, so I don't really see that as being
comparable.

The only thing we used to have to go on was what ALTER SYSTEM did, and
then pg_basebackup went and did something different, and enough so that
they ended up conflicting with each other, leading to this discussion.

Thanks,

Stephen

Commits

  1. Doc: improve documentation about postgresql.auto.conf.

  2. Fix ALTER SYSTEM to cope with duplicate entries in postgresql.auto.conf.