RE: CBO problem
- From: "Laimutis Nedzinskas" <Laimutis.Nedzinskas@xxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 17 Jul 2006 17:38:58 -0000
You have to read Note:212809.1 Limitations of the Oracle Cost Based Optimizer
and notes on bind variable peeking and notes on histograms. Apart of bugs there
are some fundamental problems in optimization business, in short:
-Bind variables basically eliminate histograms. Bind variable peeking is just
a plain guess.
-Histograms do not always represent accurate data distribution.
-In many cases multi column predicate cardinalities is just a plain guess.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Nirmalya Das
Sent: 17. júlí 2006 17:20
To: David Sharples
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: CBO problem
I thought the "stats" collection is one of the most important events to help
CBO finding the best QEP......
Are you sure you want me to turn it off?
Quoting David Sharples <davidsharples@xxxxxxxxx>:
> do you need to collect stats, if not turn it off
>
> On 17/07/06, Nirmalya Das <nirmalya@xxxxxxx> wrote:
>>
>>
>> I remember a while back there was a thread on this particular issue
>> the "Automatic Statistics Gathering" can sometimes produce
>> undesirable results and QEP. I tried to search the archives of this
>> list but could not locate the thread.
>>
>> Does any one remember that or have some suggestions on using the
>> "Automatic Statistics Gathering".
>>
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