RE: Poor performance with Histogram
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 12 Dec 2006 18:49:22 +0100
> Note that you need to force the creation of the (silly) histogram
> because "size skewonly" or "size auto" do not gather histograms for
> unique columns.
Sorry Wolfgang, on this specific point I cannot agree... In fact it
really depends on the distribution. Below you find an example.
Cheers,
Chris
SQL> create table t as select rownum n from all_objects;
Table created.
SQL> insert into t select n+1000000 from t;
51832 rows created.
SQL> commit;
Commit complete.
SQL> create unique index i on t (n);
Index created.
SQL> exec dbms_stats.gather_table_stats(user,'t',method_opt=>'for all
columns size skewonly',cascade=>true)
PL/SQL procedure successfully completed.
SQL> select count(*) from user_tab_histograms where table_name = 'T';
COUNT(*)
----------
255
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