On 05/28/2004 10:45:39 AM, Reginald.W.Bailey_at_jpmorgan.com wrote:
>
> Mladen:
>
> What is BCHR?
>
Reginald, I apologize for making a jovial reference without explaining it. BCHR stands for
"Buffer Cache Hit Ratio" and is sometimes used as an ultimate measure of system performance,
much in the same fashion as when witch doctors predict weather. This measure was originally
introduced by Oracle, who even devoted a chapter the tuning book devoted to tuning the
BCHR. There were 2 tables (one of them was X$KCBCBH and I forgot the name of the other one)
which DBA was supposed to use to get the BCHR sufficiently high. The whole alchemy went on
until another esteemed member of this list, Mr. Anjo Kolk, asked a completely illogical and
outrageous question: how do you tune an application, if you don't know what the application
is waiting for and how the time is spent? He also developed so called "wait interface" and
there was a very thick document, available on Metalink, describing oracle wait events for
Oracle7. The whole philosophy was taken to the new heights by Cary Millsap in his book
"Optimizing Oracle Performance".
--
Mladen Gogala
Oracle DBA
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Received on Fri May 28 2004 - 10:02:37 CDT
