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Re: Freezing is not WAL-logged

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: Freezing is not WAL-logged
Date: 2006-10-20 13:53:08
Message-ID: 7718.1161352388@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-bugs
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> My idea was to move relminxid to a new pg_class_nt non-transactional
> catalog in 8.3, but we certainly need to give a solution for the problem
> in 8.2.

Didn't we pretty much shoot down the idea of a nontransactional
extension catalog as being not worth the trouble?

> I don't remember why I concluded that we were safe against this
> problem, but you are right that we aren't.

I think there may be another set of issues here too: what about PITR?
As things stand, neither hint-bit settings nor FrozenXID replacement
are guaranteed to get propagated to a PITR slave.

We don't propagate CLOG truncation to a slave either, which means that
to some extent it'd have the ability to re-set hint bits for itself
after coming up.  This isn't bulletproof though; most obviously in
the case where the PITR replay (or hot-slave lifespan) exceeded
4G transactions.

Can we fix it so it's sufficient to propagate FrozenXID replacement
to the slave?  If we have to turn hint-bit setting into a logged
operation, that *will* be expensive.

			regards, tom lane

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Next:From: Jim C. NasbyDate: 2006-10-20 13:58:46
Subject: Re: Freezing is not WAL-logged
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