RE: Optimizer change from 8i-9i

  • From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
  • To: "Wolfgang Breitling" <breitliw@xxxxxxxxxxxxx>
  • Date: Wed, 11 May 2005 15:43:13 +0200

Hi Wolfgang

>while I agree with you that setting optimizer_features_enable to a back
>release is not the same as running the optimizer at that release level,
>this is actually not a good example in this context as
>complex_view_merging is set to false by =

The aim of my example was simply to show that even if you run the RBO =
different execution plans can be generated during the migration from 8i =
to 9i. Of course in this special case you could probably disable =
complex_view_merging in 9i to get the old behaviour. Nevertheless, with =
default configuration the RBO is different in the two versions. =
Therefore saying that the RBO hasn't changed since 7.3 is a tale!


PS: My guess is that the core of the RBO itself has not changed (except, =
perhaps, to fix bugs). But, before a statement is send to it, some =
transformation can be applied (like complex view merging). Therefore =
another execution plan is generated because the RBO works on a different =
statement and not because the RBO itself has changed.

Other related posts: