From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jim C. Nasby <jnasby@pervasive.com>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: WAL logging of SELECT ... INTO command
Date: Wed, 22 Mar 2006 10:06:05 -0500
Message-ID: <16480.1143039965@sss.pgh.pa.us> (raw)
In-Reply-To: <20060322131910.GC15742@pervasive.com>
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>
"Jim C. Nasby" <jnasby@pervasive.com> writes:
>> PITR wants all changes. Without PITR we can optimise 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.
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, jnasby@pervasive.com, simon@2ndquadrant.com
Subject: Re: WAL logging of SELECT ... INTO command
In-Reply-To: <16480.1143039965@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox