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Re: Revitalising VACUUM FULL for 8.3

From: Hannu Krosing <hannu(at)skype(dot)net>
To: Zeugswetter Andreas ADI SD <ZeugswetterA(at)spardat(dot)at>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Revitalising VACUUM FULL for 8.3
Date: 2007-03-01 14:54:44
Message-ID: 1172760884.3216.37.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
Ühel kenal päeval, N, 2007-03-01 kell 15:03, kirjutas Zeugswetter
Andreas ADI SD:
> > > > 		-- start the VACUUM from the first non-filled block
> > > > 
> > > > So if we do this, we wouldn't need to worry about HOT tuples at
> all, 
> > > > nor would we need to wait until all transactions are gone.
> > > 
> > > You need to wait until you are allowed to truncate if you want 
> > > concurrency.
> > > Or a concurrent scan might miss a row, because the visible tuple got
> 
> > > truncated away.
> > 
> > I was not suggesting that we remove visible rows through truncation.
> 
> Sure, unless you suggest to not truncate during this vacuum run ?
> But we are talking about vacuum full, so truncation is essential.
> 
> It was suggested to do a dummy null update to move live tuples up front.
> The old version is still visible for serializable txns.

There should probably be a wait-other-trxs to finish stage between
COMPACT and 2nd VACUUM if truncation at this cycle is absolutely needed

> Andreas
> 
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----------------
Hannu Krosing
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