Re: SQL Tuning question

Ryan Gaffuri wrote:

> First off, my explanation is going to be a bit vague since I dont have
> alot of details. However, I hope its enough to get an opinion.
>
> I was talking to a couple of DBA's and on their project they stated
> that they often have to use a hint to force the RBO. They said that
> this happens when querying off of layered views. My best guess on why
> this is so, is that the analyzer will gather statistics off the
> tables, these statistics may not be entirely valid for views made on
> top of views, so when the CBO is used, it is using poor statistics.
>
> I have seen in some books that if this happens you should consider
> re-writing your queries so that they directly access the tables. This
> could be very time consuming.
>
> Just looking for some general comments on this?

No version so I will assume 8i or 9i.

RBO is close to dead. Time to move to CBO which means having current valid statistics.

Never layer views on top of views unless performance doesn't matter. Of course it takes time
to rewrite them. It takes time to tune layered views too.

Daniel Morgan Received on Fri Jan 17 2003 - 10:51:55 CST