Re: Database Buffer Cache Hit Ratio

Number 1 question around your issue with BCHR - why does this matter?

There have been a number of discussions around topic, and several proofs have been offered that a good DBA can basically create any ratio value desired.

Conclusion is simple - don't use Buffer Cache Hit Ratio as a meaningful indicator by itself. First determine that there is indeed a problem that needs to be tuned (user are complaining), then find out what is waiting and why it's waiting.

A lot of DBA energy has been wasted over the years in achieving good BCHRs with absolutely no, or minimal, impact on performance. Sadly, the only benefit of this mode of operation is 'CYA' and incorrectly prove that either Oracle sucks or the hardware sucks. Even Oracle's 9i tuning course says 'tune BCHR only after other tuning has been accomplished', something that many DBAs (and instructors) overlook.

You might wish to read Oracle's Perforrmance Tuning Guide, in the Oracle9i documentation set. It is a lot more meaningful than the 8i tuning guide.

Also, if not already, you may want to get familiar with stats pack AND http://www.oraperf.com for assistance in analyzing statspack info.

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Hans Forbrich                            
Canada-wide Oracle training and consulting
mailto: Fuzzy.GreyBeard_at_gmail.com   
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