RE: Which plan is better - what COST really means ?

Jonathan also mentioned to me that the cost estimate should be = multiplied by 'sreadtim'
when running 9i with system statistics (cpu costing) enabled. The cost = multiplied by this
value is the assumed time to complete.

Cost is not the time estimate itself and this is what I was trying to = discern from
Jonathan's earlier post. What I understand Jonathan was trying to say = was that cost is
the value that should be multiplied by a time value estimate to = determine the estimated
time to complete.

The issue I still find for myself is that I rarely see this estimated = value be reliably
close to the actual value for response time. Perhaps in the perfect = world, and I guess
that's where the optimizer thinks it lives :), it would. But, even on a = test database
where I am the only user executing a single query, I don't often see the = costed time
estimate match the actual.

I just wish the optimizer was perfect....then again, if that were the = case, many of us
would have to find other ways to fill our time currently allotted to = query optimization.
:)

Karen Morton
Hotsos Enterprises, Ltd.
http://www.hotsos.com
Upcoming events at http://www.hotsos.com/education/schedule.html

=20

-----Original Message-----
From: Mladen Gogala [mailto:gogala_at_sbcglobal.net]=20 Sent: Friday, January 14, 2005 3:23 PM
To: karen.morton_at_hotsos.com
Cc: oracle-l_at_freelists.org
Subject: Re: Which plan is better - what COST really means ?

On 01/14/2005 05:43:53 PM, Karen Morton wrote:

> In what time measurement is the cost? Seconds, centiseconds, =3D=20
> microseconds? =3D20

The measurements are in centiseconds, that is soft clock ticks. That is = one of the few
things that wasn't converted to microseconds with =20 oracle9i
--=20
Mladen Gogala
Oracle DBA

--
http://www.freelists.org/webpage/oracle-l