Re: Cost Vs. Rules Based Optimizers
Date: 26 Jan 1995 00:26:20 GMT
Message-ID: <3g6q7c$ssn$1_at_mhadg.production.compuserve.com>
Interesting article regarding the CBO. We're struggling with
many of the unpredictabilities of CBO as we prepare to deliver a
warehouse app. One bad item - the CBO will be used if at least
ONE of the tables referenced in a query has statistics in the
data dictionary. The DBA needs to be on top of the statistics
issue, or your performance suffers. An application that was
tuned on delivery can slowly "go out of tune" as the data
changes.
Developers need to be sync with the DBA's ANALYZE schedule. You
can spend all night tweaking a query and get it right, only to
have it "un-tuned" by a re-ANALYZE on the referenced tables the
next day.
I would encourage anyone with additional gotchas to follow up on this post - it's a pretty significant issue.
Rich Gaston, CellularOne Received on Thu Jan 26 1995 - 01:26:20 CET