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Re: Revitalising VACUUM FULL for 8.3

From: "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: "Hannu Krosing" <hannu(at)skype(dot)net>,<pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Revitalising VACUUM FULL for 8.3
Date: 2007-03-01 14:03:39
Message-ID: E1539E0ED7043848906A8FF995BDA57901CAFFE8@m0143.s-mxs.net (view raw or flat)
Thread:
Lists: pgsql-hackers
> > > 		-- 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.

Andreas

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