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Re: Fed Up with being a DBA

From: Joel Garry <joel-garry_at_home.com>
Date: 12 Sep 2003 15:59:19 -0700
Message-ID: <91884734.0309121459.3440f29c@posting.google.com>


"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...

CBO can optimize _some_ queries better than RBO. To get an idea which ones, look at all the hints. However, the OP has a good point, and that is, those are rarely relevant to OLTP queries in commercial packages that have been wrung out for years. What I've seen happen is (assuming proper statistics), most queries have about the same performance, some have better performance, and a few (perhaps oddly written from an Oracle viewpoint) have much worse performance. Those few can be painful, especially if the commercial package has some sort of layer such as an OCI generator between the SQL engine and the code that disallows passing hints. But even without that issue, thousands of tables with concomitant code to deal with them makes it quite a big deal to run an explain plan on every query, as Daniel says is necessary. I say, jeez, if CBO is so great, why can't it reduce to RBO? All RBO is, after all, is definite rules on how to access the db given certain sql. CBO has had bugs in the past, although now it is mostly good (but check out those release notes). But there is no easy way up, and I think it is a mistake for Oracle to be so flippant about backwards compatibility. Software for the ages needs to be designed and written for the ages.

I get paid by the hour too, but that doesn't mean it's an easy sell to convince people to give you hours to do maintenance they consider unnecessary overhead. Much easier to just accept non-O salespeople's word that the latest and greatest buzz is better, so throw out the old and replace it with evil incarnate.

>
>
> "Domenic G." <domenicg_at_hotmail.com> wrote in message
> news:c7e08a19.0309111612.69697120_at_posting.google.com...
> > I don't know about all of you, but I'm fed up with being a DBA and
> > working in the IT industry. I've been an Oracle DBA for several years
> > now and pride myself on knowing Oracle like the back of my hand.
> >
> > Here are my gripes ...
> >
> > - third party apps that run on Oracle and designed like junk.
> > - third party apps that insist on "GRANT DBA TO ..."
> > - schemas with FKs that aren't indexed (man do I hate that!)
> > - poorly written queries (EXISTS and IN are like cryptonite!)
> > - the COST based optimizer which outsmarts itself more often than not
> > so that I have to to /*+ ORDERED INDEX(a b) USE_NL (w x y z) */ to
> > achieve the same thing as /*+ RULE */
> > - schemas that still use CHAR(x)
> > - DBAs who use DBCA to create a DB and it adds in all that unwanted
> > JUNK!!
> >
> > Cheers ...
> > Domenic

jg

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Received on Fri Sep 12 2003 - 17:59:19 CDT

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