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From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Jim C. Nasby <jnasby@pervasive.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PFC <lists@peufeu.com>
Cc: Mitchell Skinner <mitch@arctur.us>
Cc: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Big IN() clauses etc : feature proposal
Date: Thu, 11 May 2006 13:02:57 -0500
Message-ID: <1147370576.9755.81.camel@state.g2switchworks.com> (raw)
In-Reply-To: <20060511171806.GJ99570@pervasive.com>
References: <op.s8916gm6cigqcu@apollo13>
	<20060509113337.M90693@vesihiisi.cksoft.de>
	<op.s893vzcpcigqcu@apollo13>
	<20060509103632.GD29652@svana.org>
	<op.s897j60qcigqcu@apollo13>
	<1147190285.32304.43.camel@firebolt>
	<op.s9alu1vhcigqcu@apollo13>
	<16680.1147201981@sss.pgh.pa.us>
	<20060510190011.GO99570@pervasive.com>
	<22558.1147307514@sss.pgh.pa.us>
	<20060511171806.GJ99570@pervasive.com>

On Thu, 2006-05-11 at 12:18, Jim C. Nasby wrote:
> On Wed, May 10, 2006 at 08:31:54PM -0400, Tom Lane wrote:
> > "Jim C. Nasby" <jnasby@pervasive.com> writes:
> > > On Tue, May 09, 2006 at 03:13:01PM -0400, Tom Lane wrote:
> > >> PFC <lists@peufeu.com> writes:
> > >>> Fun thing is, the rowcount from a temp table (which is the problem here)  
> > >>> should be available without ANALYZE ; as the temp table is not concurrent,  
> > >>> it would be simple to inc/decrement a counter on INSERT/DELETE...
> > >> 
> > >> No, because MVCC rules still apply.
> > 
> > > But can anything ever see more than one version of what's in the table?
> > 
> > Yes, because there can be more than one active snapshot within a single
> > transaction (think about volatile functions in particular).
> 
> Any documentation on how snapshot's work? They're a big mystery to me.
> :(

http://www.postgresql.org/docs/8.1/interactive/mvcc.html

Does the concurrency doc not cover this subject well enough (I'm not
being sarcastic, it's a real question)

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