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