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

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Mon, 01 Mar 2004 21:29:55 -0700
Message-Id: <6.0.3.0.2.20040301212334.02b19138@pop.centrexcc.com>

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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Received on Mon Mar 01 2004 - 22:26:56 CST