actually with this parameter description I pointed
you to, there were pointers to perf tuning guide:
<quote about optimizer_dynamic_sampling
parameter>
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 -----
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.
> --
> Please see
the official ORACLE-L FAQ: http://www.orafaq.net> --
> Author: Jamadagni, Rajendra
> INET:
Rajendra.Jamadagni@espn.com>
> Fat City Network Services -- 858-538-5051 http://www.fatcity.com> San
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Received on Tue Dec 30 2003 - 17:29:35 CST
