Re: More on dbms_stats
- From: Mladen Gogala <gogala@xxxxxxxxxxxxx>
- To: mgogala@xxxxxxxxxxxxxxxxxxxx
- Date: Wed, 10 Aug 2005 23:19:01 +0000
On 08/10/2005 05:48:23 PM, Mladen Gogala wrote:
> Wolfgang Breitling wrote:
>
> > It potentially, and likely, creates an awful lot of histograms exactly
> > BECAUSE the method_opt setting of 'for all columns size 1' is ignored
> > and replaced with 'for all columns size auto'.
> >
> I prefer skewed columns, that is the columns from SYS.COL_USAGE$.
As was gently and privately pointed out, I badly mixed things up yet again.
The table SYS.COL_USAGE$ is used by 'FOR ALL COLUMNS SIZE AUTO' method while
FOR ALL COLUMNS SIZE SKEWONLY computes histograms for all columns. I tried
accusing the manuals, but they did a good job explaining that:
- integer : Number of histogram buckets. Must be in the range [1,254].
- REPEAT : Collects histograms only on the columns that already have histograms.
- AUTO : Oracle determines the columns to collect histograms based on data
distribution and the workload of the columns.
- SKEWONLY : Oracle determines the columns to collect histograms based on the
data distribution of the columns.
I must be growing old.
--
Mladen Gogala
http://www.mgogala.com
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