Re: Cost Base Optimizer on 3 table select

From: Gerard M. Averill <gaverill_at_chsra.wisc.edu>
Date: Fri, 23 Oct 98 15:46:45 GMT
Message-ID: <70q88s$c92$1@news.doit.wisc.edu>

In article <Pine.OSF.3.95.981022084650.2130A-100000_at_gonzo.wolfenet.com>, Jeremiah Wilton <jeremiah_at_wolfenet.com> wrote:
>On Thu, 22 Oct 1998, Billy Verreynne wrote:
>>
>> Sadly, that is not a good idea when using CBO. Experience has taught me that
>> the safest way to write SQLs that perform consistently on Oracle using the
>> same execution plan is via hints.
>
>Doesn't that defeat the whole purpose of the CBO? Admittedly, using the
>CBO is still a little cumbersome. Scripting the analyze is necessary, as

<snip>

The whole purpose of the CBO, I would think, is to alleviate the need to always concern oneself fully with the details of a given query's execution plan. When it works well, fine; but I agree with Billy, there are times when using hints is the most efficient way to ensure a consistent execution plan. The CBO is a good attempt to approximate knowledge about your data, but when one has more complete knowledge, why not make use of it?

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Gerard M. Averill, Associate Researcher CHSRA, University of Wisconsin - Madison GAverill_at_chsra.wisc.edu Received on Fri Oct 23 1998 - 10:46:45 CDT