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Re: Dead Space Map

From: Hannu Krosing <hannu(at)skype(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dead Space Map
Date: 2006-02-28 07:52:24
Message-ID: 1141113144.3775.13.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
Ühel kenal päeval, E, 2006-02-27 kell 13:17, kirjutas Tom Lane:
> Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> > Vacuum will need to be modified to use index lookups to find index tuples 
> > corresponding the dead heap tuples. Otherwise you have to scan through 
> > all the indexes anyway.
> 
> This strikes me as a fairly bad idea, because it makes VACUUM dependent
> on correct functioning of user-written code --- consider a functional
> index involving a user-written function that was claimed to be immutable
> and is not.  There are concurrency-safety issues too, I think, having to
> do with the way that btree ensures we don't delete any index tuple that
> some scan is stopped on.
> 
> > * vacuuming pages one by one as they're written by bgwriter
> 
> That's not happening.  VACUUM has to be a transaction 

WHY does vacuum need to be a tranasction ? I thought it was a programmer
workload optimisation (aka. lazyness :) ) to require ordinary lazy
vacuum to be in transaction.

There is no fundamental reason, why vacuum needs to run in a transaction
itselt.

-----------------
Hannu



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