From: Jim C. Nasby <jnasby@pervasive.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: WAL logging of SELECT ... INTO command
Date: Wed, 22 Mar 2006 09:14:34 -0600
Message-ID: <20060322151434.GG15742@pervasive.com> (raw)
In-Reply-To: <16480.1143039965@sss.pgh.pa.us>
References: <20060321122211.GU15742@pervasive.com>
<1142973230.24487.501.camel@localhost.localdomain>
<20060322124732.GA15742@pervasive.com>
<1143032914.24487.632.camel@localhost.localdomain>
<20060322131910.GC15742@pervasive.com>
<16480.1143039965@sss.pgh.pa.us>
On Wed, Mar 22, 2006 at 10:06:05AM -0500, Tom Lane wrote:
> "Jim C. Nasby" <jnasby@pervasive.com> writes:
> >> PITR wants all changes. Without PITR we can optimize certain logging
> >> actions.
>
> > The only change here is that we're creating a new table based on the
> > results of a SELECT. If that SELECT doesn't use anything that's
> > non-deterministic, then the machine doing the recovery should already
> > have all the data it needs, provided that we log the SELECT that was
> > used in the CTAS.
>
> This is based on a fundamental misconception about the way PITR
> log-shipping works. We log actions at the physical level (put this
> tuple here), not the logical here's-the-statement-we-executed level.
> The two approaches cannot mix, because as soon as there's any physical
> discrepancy at all, physical-level actions would be incorrectly applied
> to the slave database.
Oh, so in other words, SELECT * INTO temp FROM table is inherently
non-deterministic at the physical level, so the only way to be able to
allow PITR to work is to duplicate all the physical changes. Darn.
--
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, simon@2ndquadrant.com
Subject: Re: WAL logging of SELECT ... INTO command
In-Reply-To: <20060322151434.GG15742@pervasive.com>
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