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Home -> Community -> Mailing Lists -> Oracle-L -> RE: db_file_mutliblock_read_count and physical IO
I agree with your use of the word at the level of abstraction that =
resides
one level beneath the Oracle DBMS. And the Concepts Guide for 10.1.0.2 =
does
use the name "data blocks" for all Oracle blocks, regardless of segment
type. So you are correct.
(I would argue, by the way, that the name of a block should reflect the =
type
of its potential content, not its actual present content, so I would say
that even an empty block is a "data block.")
My concern is that people who have learned ridiculous nonsense like the
"80/20 rule of indexing" and that "Oracle reads records from disk into =
RAM"
might also not understand that the blocks being read can be from =
segments of
different types. In particular, I find people to be somewhat surprised =
on
occasion when they see an undo block being read via one of the kernel's =
read
events.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
Upcoming events:
- Performance Diagnosis 101: 9/14 San Francisco, 10/5 Charlotte, 10/26
Toronto
- SQL Optimization 101: 8/16 Minneapolis, 9/20 Hartford, 10/18 New =
Orleans
- Hotsos Symposium 2005: March 6-10 Dallas
- Visit www.hotsos.com for schedule details...
-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Niall Litchfield
Sent: Thursday, August 19, 2004 3:47 AM
To: oracle-l_at_freelists.org
Subject: Re: db_file_mutliblock_read_count and physical IO
On Wed, 18 Aug 2004 11:54:33 -0500, Cary Millsap
<cary.millsap_at_hotsos.com> wrote:
> I think it's important to realize that even the Oracle Reference =
manual =3D
> is
> subtly wrong in two ways.
<snip>
> The errors:
>=20
> 1. It's not just data blocks. It's index blocks, undo blocks, and so =
on.
> It's Oracle blocks.
<pet rant>
I'm not sure I count this as an *error* - sure it is a common way of
looking at things DATA vs INDEX tablespaces anyone? It might even be
the accepted term and so we will probably have to live with it, but to
my mind data is data regardless of the type of logical object it
belongs to. An index contains data, an undo segment contains data, the
stored code of for example packages contains data. The only blocks to
my mind that do not contain data are empty blocks. Unless the reading
of empty blocks is also counted (which it might be I'm ignorant on
this) then I don't like the distinction in this case. I'd say that the
documentation was subtly correct and the rest of us were wrong.
=20
</pet rant>
--=20
Niall Litchfield
Oracle DBA
http://www.niall.litchfield.dial.pipex.com
-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Thu Aug 19 2004 - 09:32:08 CDT
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