Date: Mon, 30 Jun 2008 17:43:18 +0200
From: Peter Schuller <peter.schuller@infidyne.com>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: VACUUM ANALYZE blocking both reads and writes to a
	table
Message-ID: <20080630154318.GB15756@hyperion.scode.org>
References: <20080630145903.GA15197@hyperion.scode.org>
	<20080630152515.GF10311@alvh.no-ip.org>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature"; boundary="ZoaI/ZTpAVc4A5k6"
Content-Disposition: inline
In-Reply-To: <20080630152515.GF10311@alvh.no-ip.org>
User-Agent: Mutt/1.5.18 (2008-05-17)


--ZoaI/ZTpAVc4A5k6
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Actually, while on the topic:

>     date: 2007-09-10 13:58:50 -0400;  author: alvherre;  state: Exp;  lin=
es: +6 -2;
>     Remove the vacuum_delay_point call in count_nondeletable_pages, becau=
se we hold
>     an exclusive lock on the table at this point, which we want to releas=
e as soon
>     as possible.  This is called in the phase of lazy vacuum where we tru=
ncate the
>     empty pages at the end of the table.

Even with the fix the lock is held. Is the operation expected to be
"fast" (for some definition of "fast") and in-memory, or is this
something that causes significant disk I/O and/or scales badly with
table size or similar?

I.e., is this enough that, even without the .4 bug, one should not
really consider VACUUM ANALYZE non-blocking with respect to other
transactions?

(I realize various exclusive locks are taken for short periods of time
even for things that are officially declared non-blocking; the
question is whether this falls into this category.)

--=20
/ Peter Schuller

PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>'
Key retrieval: Send an E-Mail to getpgpkey@scode.org
E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org


--ZoaI/ZTpAVc4A5k6
Content-Type: application/pgp-signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.9 (FreeBSD)

iEYEARECAAYFAkho/xQACgkQDNor2+l1i32D/gCeLbh7tnWdch/ScxIOIcEreulG
T4sAoJgFti+zggEqnUHz79t/sK6ma8n6
=hpoH
-----END PGP SIGNATURE-----

--ZoaI/ZTpAVc4A5k6--