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Re: pg_upgrade if 'postgres' database is dropped

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_upgrade if 'postgres' database is dropped
Date: 2011-10-28 14:07:51
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Robert Haas wrote:
> >> But regardless of which database it uses to *generate* the dump, the
> >> dump itself will *always* contain this, right at the very beginning:
> >>
> >> \connect postgres
> >>
> >> That line is in fact hard-coded as a literal string in pg_dumpall.c.
> >> It seems like the easiest fix here might be to just remove that line
> >> from the dump, because AFAICS it's completely pointless. ?During the
> >> time for which that setting is in effect, we're just restoring
> >> globals, so it shouldn't matter which database we're connected to;
> >> only that we have a valid connection. ?So trying to switch the
> >> connection from whatever the user is connected to currently to
> >> postgres doesn't accomplish anything useful, but it does make it
> >> possible for dump restoration to unnecessarily fail.
> >
> > If you remove that line,
> I'm happy to do that, unless someone can see a hole in my logic.
> > I can modify pg_upgrade to use template1
> > instead of postgres, and then the user should just remove the postgres
> > database from the new cluster before the upgrade --- we can give them a
> > clear error message on that.
> What I would prefer is to have the upgrade succeed, and just ignore
> the existence of a postgres database in the new cluster.  Maybe give
> the user a notice and let them decide whether they wish to take any
> action.  I understand that failing is probably less code, but IMHO one
> of the biggest problems with pg_upgrade is that it's too fragile:
> there are too many seemingly innocent things that can make it croak
> (which isn't good, when you consider that anyone using pg_upgrade is
> probably in a hurry to get the upgrade done and the database back
> on-line).  It seems like this is an opportunity to get rid of one of
> those unnecessary failure cases.

OK, then the simplest fix, once you modify pg_dumpall, would be to
modify pg_upgrade to remove reference to the postgres database in the
new cluster if it doesn't exist in the old one.  That would allow
pg_upgrade to maintain a 1-1 matching of databases in the old and new
cluster --- it allows the change to be locallized without affecting much

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + It's impossible for everything to be true. +

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Subject: Re: pg_upgrade if 'postgres' database is dropped
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