From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: Erik Rijkers <er@xs4all.nl>, Kevin Grittner <kgrittn@mail.com>,
	pgsql-hackers@postgresql.org, Andres Freund <andres@2ndquadrant.com>
Subject: Re: foreign key locks
In-reply-to: <20130118200204.GH4063@alvh.no-ip.org>
References: <20121129152326.69330@gmx.com>
	<20121129160220.GA4942@alvh.no-ip.org>
	<20121129161654.GB4942@alvh.no-ip.org>
	<b1a78c715f9195e6f96546c8e723afd8.squirrel@webmail.xs4all.nl>
	<20121228204847.GD4150@alvh.no-ip.org>
	<20130110210040.GB4110@alvh.no-ip.org>
	<20130118200204.GH4063@alvh.no-ip.org>
Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
	message dated "Fri, 18 Jan 2013 17:02:04 -0300"
Date: Fri, 18 Jan 2013 15:37:47 -0500
Message-ID: <28623.1358541467@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> The reason is that there is an (unknown to me) rule that there must be
> some data not associated with a buffer:

> 	/*
> 	 * NOTE: We disallow len == 0 because it provides a useful bit of extra
> 	 * error checking in ReadRecord.  This means that all callers of
> 	 * XLogInsert must supply at least some not-in-a-buffer data. [...]
> 	 */

> This seems pretty strange to me.  And having the rule be spelled out
> only in a comment within XLogInsert and not at its top, and not nearby
> the XLogRecData struct definition either, seems pretty strange to me.
> I wonder how come every PG hacker except me knows this.

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.

			regards, tom lane


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