RE: optimizer_ ???
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: "Niall Litchfield" <niall.litchfield@xxxxxxxxx>
- Date: Tue, 26 Apr 2005 23:01:38 +0200
Niall
>showing me that if you change a parameter the plan will change tells
>me very little about performance - it does tell me about a bit about
>behaviour, showing me response time does and - so far as I can tell -
>there aren't any examples of improved response time from setting these
>parameters. Its as if the tuning goal has become 'favour nested loops'
>rather than 'impove end-user experience'.
In the example I posted some hours ago shows that:
SQL> ALTER SESSION SET OPTIMIZER_INDEX_CACHING=3D0;
SQL> SELECT count(*)
2 FROM t t1, t t2
3 WHERE t1.id =3D3D t2.col1(+) AND t2.col1(+) > 900;
Elapsed: 00:00:00.07
SQL> ALTER SESSION SET OPTIMIZER_INDEX_CACHING=3D90;
SQL> SELECT count(*)
2 FROM t t1, t t2
3 WHERE t1.id =3D3D t2.col1(+) AND t2.col1(+) > 900;
Elapsed: 00:00:01.05
This means that just by setting OIC there is a difference of factor =
*15*.
Chris
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