From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@2ndquadrant.com>
cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Erik Rijkers <er@xs4all.nl>,
	Kevin Grittner <kgrittn@mail.com>, pgsql-hackers@postgresql.org
Subject: Re: foreign key locks
In-reply-to: <20130118204643.GA4359@awork2.anarazel.de>
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	<20121228204847.GD4150@alvh.no-ip.org>
	<20130110210040.GB4110@alvh.no-ip.org>
	<20130118200204.GH4063@alvh.no-ip.org>
	<28623.1358541467@sss.pgh.pa.us>
	<20130118204643.GA4359@awork2.anarazel.de>
Comments: In-reply-to Andres Freund <andres@2ndquadrant.com>
	message dated "Fri, 18 Jan 2013 21:46:43 +0100"
Date: Fri, 18 Jan 2013 16:01:18 -0500
Message-ID: <693.1358542878@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Andres Freund <andres@2ndquadrant.com> writes:
> On 2013-01-18 15:37:47 -0500, Tom Lane wrote:
>> I doubt it ever came up before.  What use is logging only the content of
>> a buffer page?  Surely you'd need to know, for example, which relation
>> and page number it is from.

> It only got to be a length of 0 because the the data got removed due to
> a logged full page write. And the backup block contains the data about
> which blocks it is logging in itself.

And if the full-page-image case *hadn't* been invoked, what then?  I
still don't see a very good argument for xlog records with no fixed
data.

> I wonder if the check shouldn't just check write_len instead, directly
> below the loop that ads backup blocks.

We're not changing this unless you can convince me that the read-side
error check mentioned in the comment is useless.

			regards, tom lane


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