From: VJK <vjkmail@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-performance@postgresql.org
Subject: Re: Deleting bytea, autovacuum, and 8.2/8.4 differences
Date: Mon, 15 Mar 2010 12:37:57 -0400
Message-ID: <600ad6df1003150937t68b6c1d4k976fb5504e448f3c@mail.gmail.com> (raw)
In-Reply-To: <17919.1268664802@sss.pgh.pa.us>
References: <20100313211742.GC2178@comppasch2>
<600ad6df1003141822u297522dbvf1f7187d0eee803@mail.gmail.com>
<600ad6df1003150654if287c53k301f5763e95a3540@mail.gmail.com>
<4B9E4762.7060703@2ndquadrant.com>
<17919.1268664802@sss.pgh.pa.us>
On Mon, Mar 15, 2010 at 10:53 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Greg Smith <greg@2ndquadrant.com> writes:
> > VJK wrote:
> >> Since Pg does not use the concept of rollback segments, it is unclear
> >> why deletion produces so much disk IO (4GB).
>
> For an example like this one, you have to keep in mind that the
> toast-table rows for the large bytea value have to be marked deleted,
> too. Also, since I/O happens in units of pages, the I/O volume to
> delete a tuple is just as much as the I/O to create it.
>
That makes sense.
> regards, tom lane
>
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: vjkmail@gmail.com, tgl@sss.pgh.pa.us
Subject: Re: Deleting bytea, autovacuum, and 8.2/8.4 differences
In-Reply-To: <600ad6df1003150937t68b6c1d4k976fb5504e448f3c@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox