Re: cost
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Tue, 06 Apr 2004 04:15:48 -0600
Does not appears to make a difference in this case:
SQL> alter session set "_new_initial_join_orders"=false;
Session altered.
SQL> explain plan set statement_id='00002' for
2 select e.ename, d.dname
3 from emp e inner join dept d
4 using (deptno)
5 where d.dname = 'RESEARCH'
6 /
Explained.
SQL> @xplain 00002
-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 110 | 6 (34)|
|* 1 | HASH JOIN | | 5 | 110 | 6 (34)|
|* 2 | TABLE ACCESS FULL | DEPT | 1 | 13 | 3 (34)|
| 3 | TABLE ACCESS FULL | EMP | 14 | 126 | 3 (34)|
-------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("E"."DEPTNO"="D"."DEPTNO")
2 - filter("D"."DNAME"='RESEARCH')
At 02:16 AM 4/6/2004, you wrote:
> > My guess would be that this is a deliberate
> > heuristic introduced some time around 9
> > to avoid nested loop full tablescans when
> > the numbers are small.
>
>I wonder could this behaviour be changed with _new_initial_join_orders
>parameter? (Don't have a chance to test it myself right now)
>
>Tanel.
>
>
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Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com
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