Re: Should we stop analyzing?

Tanel Poder Tue, 30 Dec 2003 16:37:08 -0800

actually with this parameter description I pointed you to, there were pointers to perf tuning guide:

You control dynamic sampling with the OPTIMIZER_DYNAMIC_SAMPLING parameter, which can be set to a value from 0 to 10.

A value of 0 means dynamic sampling will not be done.
A value of 1 (the default) means dynamic sampling will be performed if all of the following conditions are true:
- There is more than one table in the query.
- Some table has not been analyzed and has no indexes.
- The optimizer determines that a relatively expensive table scan would be required for this unanalyzed table.
Increasing the value of the parameter results in more aggressive application of dynamic sampling, in terms of both the type of tables sampled (analyzed or unanalyzed) and the amount of I/O spent on sampling.

</quote>

I haven't tested what happens when you already have statistics and specify dynamic sampling hint, then which stats are used after all... but it's very easy to check out with 10053 trace, it has a lines about dynamic sampling in it when Oracle uses or tries to use dynamic sampling.

Tanel.

----- Original Message -----

From: "Jamadagni, Rajendra" <[EMAIL PROTECTED]>

To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>

Sent: Wednesday, December 31, 2003 12:24 AM

Subject: RE: Should we stop analyzing?

> Tanel,
>
> I know the values, you are missing my question ... let me re-phrase it ...
>
> 1. To have CBO use dynamic sampling do you have to specify the hint?
> or
> 2. CBO will do that automatically?
>
> Just to let you know, Oracle 9ir2 docs main page is my home page on Mozilla firebird browser and Metalink is my homepage on IE.
> Raj
> --------------------------------------------------------------------------------
> Rajendra dot Jamadagni at nospamespn dot com
> All Views expressed in this email are strictly personal.
> QOTD: Any clod can have facts, having an opinion is an art !
>
>
> -----Original Message-----
> Sent: Tuesday, December 30, 2003 2:44 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Go to tahiti.oracle.com and search for the optimizer_dynamic_sampling
> parameter, you'll see descriptions for it's different values there.
>
> Tanel.
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> Author: Jamadagni, Rajendra
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Re: Should we stop analyzing?

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