Received: from maia.hub.org (unknown [200.46.208.211])
	by mail.postgresql.org (Postfix) with ESMTP id EFD89631E46
	for <pgsql-hackers-postgresql.org@mail.postgresql.org>;
	Sun, 25 Apr 2010 16:02:36 -0300 (ADT)
Received: from mail.postgresql.org ([200.46.204.86])
	by maia.hub.org (mx1.hub.org [200.46.208.211]) (amavisd-maia,
	port 10024) with ESMTP id 75652-01
	for <pgsql-hackers-postgresql.org@mail.postgresql.org>;
	Sun, 25 Apr 2010 19:02:14 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.7.6
Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130])
	by mail.postgresql.org (Postfix) with ESMTP id C846B63269C
	for <pgsql-hackers@postgresql.org>;
	Sun, 25 Apr 2010 16:02:25 -0300 (ADT)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
	by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id o3PJ2Njs007080;
	Sun, 25 Apr 2010 15:02:23 -0400 (EDT)
To: Jim Nasby <decibel@decibel.org>
cc: Robert Haas <robertmhaas@gmail.com>,
	Greg Sabino Mullane <greg@turnstep.com>, pgsql-hackers@postgresql.org
Subject: Re: global temporary tables 
In-reply-to: <14A49FEC-5671-4961-88CB-0A7A6A0C58A4@decibel.org> 
References: <fca910820578d251cc1d5647793c9a67@biglumber.com>
	<7796.1272125493@sss.pgh.pa.us>
	<k2y603c8f071004241016w48b9d39an2dbf6d9df2bad495@mail.gmail.com>
	<9319.1272130283@sss.pgh.pa.us>
	<FD5C55A5-5003-4C4E-8DC6-E124A13E0B68@decibel.org>
	<y2u603c8f071004241814x10e29bc8pb46cad5edc0e2a5b@mail.gmail.com>
	<18126.1272159451@sss.pgh.pa.us>
	<u2y603c8f071004241859j8317f9cai665cf3d75317930c@mail.gmail.com>
	<s2i603c8f071004241922ze1498adah728dcb8d88d59980@mail.gmail.com>
	<19198.1272162480@sss.pgh.pa.us>
	<u2h603c8f071004241957xb93a989ct5c78ff8e0f15c47b@mail.gmail.com>
	<19874.1272164562@sss.pgh.pa.us>
	<14A49FEC-5671-4961-88CB-0A7A6A0C58A4@decibel.org>
Comments: In-reply-to Jim Nasby <decibel@decibel.org>
	message dated "Sun, 25 Apr 2010 09:26:37 -0500"
Date: Sun, 25 Apr 2010 15:02:23 -0400
Message-ID: <7079.1272222143@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Virus-Scanned: Maia Mailguard 1.0.1
X-Spam-Status: No, hits=-2.105 tagged_above=-10 required=5 tests=AWL=-0.195,
	BAYES_00=-1.9, T_RP_MATCHES_RCVD=-0.01
X-Spam-Level: 
X-Archive-Number: 201004/1172
X-Sequence-Number: 161284

Jim Nasby <decibel@decibel.org> writes:
> On Apr 24, 2010, at 10:02 PM, Tom Lane wrote:
>> Yeah.  I think we also use RelFileNode as a hash tag in places, and
>> so adding a bool to it would be problematic for a couple of reasons:
>> possibly uninitialized pad bytes, and uselessly incorporating more bytes
>> into the hash calculation.

> Do we need to hash it that frequently?

Every buffer access, for instance.

> Do we insert tons of them into WAL?

Yes; the vast majority of WAL records contain one.

			regards, tom lane