Date: Mon, 5 Aug 2019 18:22:03 +0200
From: David Fetter <david@fetter.org>
To: Ian Barwick <ian.barwick@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Andres Freund <andres@anarazel.de>,
	Stephen Frost <sfrost@snowman.net>,
	Amit Kapila <amit.kapila16@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions
Message-ID: <20190805162203.GR31493@fetter.org>
References: <31697.1564784856@sss.pgh.pa.us>
 <CAOuzzgqNyQM_z0biEEBVBK9WcaLmbCyWrd5xTdf-Oxb_9pntLA@mail.gmail.com>
 <32681.1564786027@sss.pgh.pa.us>
 <CAOuzzgpDj4kLNh7=bfEYv4zXrLgRziMogcXFSHzrhn74xjYXyQ@mail.gmail.com>
 <20190803004558.jfkbngi6g64eaqku@alap3.anarazel.de>
 <CAOuzzgpuH+uvT3Yvw5KC=keEqGifSc4eXQ6DB=yrowYyre2YvA@mail.gmail.com>
 <20190803010802.rs3cz2kjq4dl4olu@alap3.anarazel.de>
 <20190803124111.2aaddumd7url5wmq@development>
 <16320.1564851579@sss.pgh.pa.us>
 <d294b0d6-c00b-8a38-864f-4943a9471a6e@2ndquadrant.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <d294b0d6-c00b-8a38-864f-4943a9471a6e@2ndquadrant.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Precedence: bulk

On Mon, Aug 05, 2019 at 03:52:07PM +0900, Ian Barwick wrote:
> On 8/4/19 1:59 AM, Tom Lane wrote:> Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> >> On Fri, Aug 02, 2019 at 06:08:02PM -0700, Andres Freund wrote:
> >>> We're WAY WAY past feature freeze. This isn't the time to rewrite guc.c,
> >>> guc-file.l to be suitable for running outside of a backend environment.
> >
> >> Right. And even if we had the code, it's not quite backpatchable (which
> >> we probably should do, considering this is a general ALTER SYSTEM issue,
> >> so not pg12-only).
> >
> >> Not to mention there's no clear consensus this is actually desirable.
> >> I'd argue forcing external tools (written in arbitrary language) to use
> >> this library (written in C), just to modify a "stupid" text file is a
> >> bit overkill. IMO duplicates don't make the file invalid, we should
> >> handle that correctly/gracefully, so I don't see why external tools
> >> could not simply append to the file. We can deduplicate the file when
> >> starting the server, on ALTER SYSTEM, or some other time.
> >
> > Yup.  I'd also point out that even if we had a command-line tool of this
> > sort, there would be scenarios where it's not practical or not convenient
> > to use.  We need not go further than "my tool needs to work with existing
> > PG releases" to think of good examples.
> 
> I suspect this hasn't been an issue before, simply because until the removal
> of recovery.conf AFAIK there hasn't been a general use-case where you'd need
> to modify pg.auto.conf while the server is not running. The use-case which now
> exists (i.e. for writing replication configuration) is one where the tool will
> need to be version-aware anyway (like pg_basebackup is), so I don't see that as
> a particular deal-breaker.
> 
> But...
> 
> > I think we should just accept the facts on the ground, which are that
> > some tools modify pg.auto.conf by appending to it
> 
> +1. It's just a text file...

So are crontab and /etc/passwd, but there are gizmos that help make it
difficult for people to write complete gobbledygook to those. Does it
make sense to discuss tooling of that type?

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate