RE: RE: query slow in 9i, but not slow in 8i

  • From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 2 Mar 2004 20:36:10 -0600

I don't have access to the data to back this up, but I have seen PARSE
call response time move from over a minute to less than a second by
eliminating histograms from the equation. I think when I last saw this,
it was an Oracle8 system.


Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

Upcoming events:
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Wolfgang Breitling
Sent: Monday, March 01, 2004 10:30 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: RE: query slow in 9i, but not slow in 8i

There surely is some "cost" involved in evaluating a histogram during
the 
parse phase, but I doubt that it will be significant enough to be 
measurable. But histograms change the estimates of the CBO and it is
quite 
possible that the presence of a histogram on a column where the content
is 
not skewed enough to really warrant a histogram can change the estimates

enough to cause the optimizer to use a different, slower access path
than 
without the histogram.

At 09:14 PM 3/1/2004, you wrote:

>I am unfortunately speaking from heresay, however I heard once that
having
>histograms all over the place can slow down parsing as they have to be
>inspected.  I was left with the impression that unless the data is
skewed
>enough to warrant a histogram then there actually is a negative cost
>associated with having too many histograms.
>
>Surely someone on this list can either support me or shoot me down on
this
>one?

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com 

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