From: Jim C. Nasby <jnasby@pervasive.com>
To: 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 12:18:06 -0500
Message-ID: <20060511171806.GJ99570@pervasive.com> (raw)
In-Reply-To: <22558.1147307514@sss.pgh.pa.us>
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>
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.
:(
> > Speaking of which, if a temp table is defined as ON COMMIT DROP or
> > DELETE ROWS, there shouldn't be any need to store xmin/xmax, only
> > cmin/cmax, correct?
>
> No; you forgot about subtransactions.
Oh, I thought those were done with cmin and cmax... if that's not what
cmin/cmax are for, then what is?
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, tgl@sss.pgh.pa.us, lists@peufeu.com, mitch@arctur.us, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Big IN() clauses etc : feature proposal
In-Reply-To: <20060511171806.GJ99570@pervasive.com>
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