Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Stephen Frost <sfrost@snowman.net>, Amit Kapila <amit.kapila16@gmail.com>, Ian Barwick <ian.barwick@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-08-02T23:05:24Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2019-08-02 18:47:07 -0400, Tom Lane wrote:
>> I don't find that to be necessary or even desirable.  Many (most?) of the
>> situations where this would be important wouldn't have access to a running
>> backend, and maybe not to any PG code at all --- what if your tool isn't
>> written in C?

> I think a commandline tool to perform the equivalent of ALTER SYSTEM on
> a shutdown cluster would be a great tool.

Perhaps, but ...

> Obviously this is widely out of scope for v12.

... this.  It's entirely insane to think we're going to produce any such
thing for v12 (much less back-patch it into prior versions).  In the short
term I don't think there's any workable alternative except to decree that
"just append to the end" is a supported way to alter pg.auto.conf.

But, as you said, it's also not sane for ALTER SYSTEM to behave that way,
because it won't cope for long with repetitive modifications.  I think
we can get away with the "just append" recommendation for most external
drivers because they won't be doing that.  If they are, they'll need to
be smarter, and maybe some command-line tool would make their lives
simpler down the line.  But we aren't providing that in this cycle.

			regards, tom lane

Commits

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

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