Re: Fed Up with being a DBA

"Alan" <alan_at_erols.com> wrote in message news:<bjt4db$mouue$1_at_ID-114862.news.uni-berlin.de>...
> I haven't run any tests to prove this, but I was told by Someone Who Should
> Know (a certfied Oracle Instructor) that CBO can't optimize a query any
> better than a _properly_ optimized RBO query. If that is true, and one is
> adept at optimizing RBO, then why go to CBO (except for reallly certain
> cases such as large queries that are too time consuming to optimize
> manually)? Just asking, not trying to make a point...
>

That's right!! -- whoever told you that was absolutely 100% correct. CBO does the right thing when you're joining entire tables, and is useful for picking up on a function-based index -- RULE cannot "see" a function-based index -- just one example. RULE also cannot see new 8i/9i features such as bitmap-join indexes -- you'll have to use COST for those with specific hints to force the plan you want. CBO by itself does not always generate the best plan. Some DBAs seem to think that all you have to do is run the stats and let Oracle do the rest -- WRONG. The other problem with CBO is that your execution plans can change drastically if somebody does something to the stats, and when you upgrade from one version of Oracle to the next.

Domenic. Received on Fri Sep 12 2003 - 17:50:51 CDT