DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma;
	h=message-id:date:from:to:subject:cc:in-reply-to:mime-version
	:content-type:content-transfer-encoding:content-disposition
	:references;
	b=aoqNABNc9FPgKwCLWuiBmVt7wkOWywsE//JlWrMmCZlX/gm+vG6ec0Zms6X+jbGXn5
	Zzoyw3XL5qIop+ozt+mdlhMGXraRej56egsZRYlF0ez5TbPywUoPsvyemCQHAKkVy5cH
	aA7kpghEvUVgEp5YNDkqr2MJ0HM8srtiMZYMY=
Message-ID: <dcc563d10807141009y422ce863v38d45a40ab720962@mail.gmail.com>
Date: Mon, 14 Jul 2008 11:09:39 -0600
From: "Scott Marlowe" <scott.marlowe@gmail.com>
To: "Paul Libbrecht" <paul@activemath.org>
Subject: Re: accidental drop table recoverable?
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>, pgsql-admin@postgresql.org
In-Reply-To: <792684B3-32A7-4F9F-ACA2-A682BF35F9E0@activemath.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
References: <53CDF98F-0AE1-49ED-A2A3-C3B1E2AF2E2E@activemath.org>
	<8259.1216046847@sss.pgh.pa.us>
	<792684B3-32A7-4F9F-ACA2-A682BF35F9E0@activemath.org>

On Mon, Jul 14, 2008 at 9:29 AM, Paul Libbrecht <paul@activemath.org> wrote=
:
>
> Le 14-juil.-08 =E0 16:47, Tom Lane a =E9crit :
>
>> You can't really "rollback" a DROP TABLE --- that corresponds directly
>> to a filesystem remove() call, and no amount of fooling around with the
>> database state will undo that.
>
> That is dark.
> I read yesterday night that actually a vacuum was advised everyday since
> otherwise there was no actual deletion. So you are telling me that, howev=
er,
> drop-table does really go to deletion right away?
>
> I'm running 7.4.5 btw.

First off, if you're gonna run 7.4.x then you should REALLY be running
the latest 7.4 version, which is 7.4.21.  You are missing almost 4
years worth of updates, and there ARE dataloss bugs in 7.4.5 which
could bite you.  But that's not the core of your issue here.

When you delete tuples in a table, postgresql doesn't delete the
actual row, it just marks it as deleted / not visible anymore.  Same
goes for the corresponding entries in an index.

Dropping or truncating a table is something else.  Now, if you do:

begin;
drop table yada;
rollback;

you'll still have your table. Same thing goes for truncate.  But once
you commit such a transaction, the table is gone.  Keep in mind that
if you don't start a transaction explicitly, then each command you
type in is a transaction unto itself, and that means that a simple
drop table statement commits as soon as it finishes.