Oracle FAQ | Your Portal to the Oracle Knowledge Grid |
![]() |
![]() |
Home -> Community -> Usenet -> c.d.o.server -> Re: CBO Subquery Limitations
> I think the point is that most people are not having problems with CBO
> and subquery performance in 9i, or at least that is my experience. Most
> performance problems, particularly those associated with database
> agnostic applications, come from bad schema design and inefficiently
> constructed queries rather than the CBO itself.
Agreed.
> Appropriate statistics
> also play a big part, as can the optimizer init parameters. I believe
> PS with CBO has these set to attempt to emulate RBO plans.
>
True. One problem we had was that AUTO_SAMPLE_SIZE has a bug which grossly underestimates certain stats for skewed data.
> Without a real example and explain plan, and preferably a TKPROF
> output, it is not really possible to tell.
I wanted to avoid posting plans because I am seeing this behaviour for a large number of queries. It was more of a general question.
Thanks for the feedback.
Matt Received on Thu Aug 11 2005 - 07:59:27 CDT
![]() |
![]() |