Re: Patch for pg_upgrade to turn off autovacuum

Bruce Momjian wrote:
> Tom Lane wrote:
> > Bruce Momjian <bruce@momjian.us> writes:
> > > I thought some more about this and I don't want autovacuum to run on the
> > > old server.  This is because pg_dumpall --binary-upgrade --schema-only
> > > grabs the datfrozenxid for all the databases at the start, then connects
> > > to each database to gets the relfrozenxids.  I don't want to risk any
> > > advancement of either of those during the pg_dumpall run.
> > 
> > Why?  It doesn't really matter --- if you grab a value that is older
> > than the latest, it's still valid.  As Robert said, you're
> > over-engineering this, and thereby introducing potential failure modes,
> > for no gain.
> 
> Uh, I am kind of paranoid about pg_upgrade because it is trying to do
> something Postgres was never designed to do.  I am a little worried that
> we would be assuming that pg_dumpall always does the datfrozenxid first
> and if we ever did it last we would have relfrozenxids before the
> datfrozenxid.  I am worried if we don't prevent autovacuum on the old
> server that pg_upgrade will be more fragile to changes in other parts of
> the system.

Hold, I overstated the fragility issue above.  I now realize that the
old system is not going to change and that I only need to worry about
future changes, where are handled by the new -b flag, so maybe we can
get away with only stopping autovacuum on the new server, but I would
need someone to verify that, and this would be a change in the way 9.0
pg_upgrade operated because it did disable autovacuum on the old and new
servers with 99.9% reliability.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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