Re: Oracle Development - Best Practice
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 9 Feb 2004 19:59:52 -0000
Tim,
The question on trust was slightly tongue in cheek,
and slightly rhetorical. There is one other possible
error though. Although autotrace clearly selects
from v$sesstat, does it tell you what it's selected,
or does it massage it first ? I get the impression
that it is adjusting the CUR gets before reporting them,
which is partly why I gave up on it some time ago
and just run a before/after snapshot of the correct
v$sesstat set from another session when I want to
be picky.
If you commit after each insert, I would have predicted
four CUR gets.
One seg header to change transaction table slot
Two undo block to record undo record
Three table block to make change
Four seg header to clear transaction table slot
and possibly
Five because commit cleanout should take place
if all you've changed is one user-data block.
But I'm not sure that commit cleanout uses CUR gets -
or maybe it does, but forgets to record them. I'll have
to run some tests.
Autotrace is very devious about not introducing measurement
error, by the way. I don't know when it happened, but in
recent versions your SQL*Plus connection starts a second
session to query the v$sesstat for the first session - so whatever
work is done taking the stats does not get included in the stats.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The educated person is not the person
who can answer the questions, but the
person who can question the answers -- T. Schick Jr
Next public appearances:
March 2004 Hotsos Symposium - The Burden of Proof
March 2004 Charlotte NC OUG - CBO Tutorial
April 2004 Iceland
One-day tutorials:
http://www.jlcomp.demon.co.uk/tutorial.html
Three-day seminar:
see http://www.jlcomp.demon.co.uk/seminar.html
____UK___February
____UK___June
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
----- Original Message -----
From: "Tim Gorman" <tim@xxxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Sunday, February 08, 2004 9:37 PM
Subject: Re: Oracle Development - Best Practice
Jonathan,
I've been worried all along :-) , that's why I posted this description of
my testing, because I may have missed or misunderstood something...
---
When you ask how much I trust AUTOTRACE, we have to remember that it is only
a before/after query of V$SESSTAT for ten specific statistics. So, if I
trust AUTOTRACE, I am trusting:
* the information in V$SESSTAT
* that these ten specific statistics are the worthwhile ones
* how much collection error is the mechanism introducing
----------------------------------------------------------------
Please see the official ORACLE-L FAQ: http://www.orafaq.com
----------------------------------------------------------------
To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx
put 'unsubscribe' in the subject line.
--
Archives are at //www.freelists.org/archives/oracle-l/
FAQ is at //www.freelists.org/help/fom-serve/cache/1.html
-----------------------------------------------------------------
Other related posts:
