Re: [GENERAL] pg_upgrade problem

Excerpts from hubert depesz lubaczewski's message of lun ago 29 14:49:24 -0300 2011:
> On Mon, Aug 29, 2011 at 06:54:41PM +0200, hubert depesz lubaczewski wrote:
> > On Fri, Aug 26, 2011 at 05:28:35PM +0200, hubert depesz lubaczewski wrote:
> > > On Fri, Aug 26, 2011 at 12:18:55AM -0400, Bruce Momjian wrote:
> > > >
> > > > OK, this was very helpful. I found out that there is a bug in current
> > > > 9.0.X, 9.1.X, and HEAD that I introduced recently when I excluded temp
> > > > tables. (The bug is not in any released version of pg_upgrade.) The
> > > > attached, applied patches should fix it for you. I assume you are
> > > > running 9.0.X, and not 9.0.4.
> > >
> > > pg_upgrade worked. Now I'm doing reindex and later on vacuumdb -az.
> >
> > vacuumdb failed. The fail looks very similar to the one I had on 9.0.4.
> >
> > After long vacuum I got:
> > INFO: vacuuming "pg_toast.pg_toast_106668498"
> > vacuumdb: vacuuming of database "etsy_v2" failed: ERROR: could not access status of transaction 3429738606
> > DETAIL: Could not open file "pg_clog/0CC6": No such file or directory.

I don't understand the pg_upgrade code here. It is setting the
datfrozenxid and relfrozenxid values to the latest checkpoint's NextXID,

/* set pg_class.relfrozenxid */
PQclear(executeQueryOrDie(conn,
"UPDATE pg_catalog.pg_class "
"SET relfrozenxid = '%u' "
/* only heap and TOAST are vacuumed */
"WHERE relkind IN ('r', 't')",
old_cluster.controldata.chkpnt_nxtxid));

but I don't see why this is safe. I mean, surely the previous
vacuum might have been a lot earlier than that. Are these values reset
to more correct values (i.e. older ones) later somehow? My question is,
why isn't the new cluster completely screwed?

I wonder if pg_upgrade shouldn't be doing the conservative thing here,
which AFAICT would be to set all frozenxid values as furthest in the
past as possible (without causing a shutdown-due-to-wraparound, and
maybe without causing autovacuum to enter emergency mode either).

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Álvaro Herrera <alvherre(at)commandprompt(dot)com>
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