Re: Correct way to accuse BCHR tuning method (Was: Hit ratio)

And I think it's important to realise that ratios are useless as a starting point in the tuning process on any system, not only Oracle. Most OS'es and databases use not instrumented correctly to deal with response time measurements (makes you wonder: If response TIME is what matters, how can you then not measure exactly that - time?) - so in the other worlds (Unix, VMS, Windows, SQL Server, MySQL, DB2....) people still beleive in the ratios because they have nothing better.

Mogens

Anjo Kolk wrote:

>BCHR tuning is useless as a starting point in the tuning process.
>
>Anjo.
>
>-----Original Message-----
>Yong Huang
>Sent: Wednesday, December 24, 2003 6:09 PM
>To: Multiple recipients of list ORACLE-L
>
>
>[This message is not technical, but educational. Readers interested in
>technical info only may want to skip]
>
>Hi, Cary and Gopal,
>
>My last message is misunderstood. Nowadays most DBAs that still use
>buffer cache hit ratio as a primary performance tuning method are those
>that rarely browse public forums. When we convince them that's a wrong
>method, we should not say "Look. I can bump up BCHR to an arbitrary
>value". If he doesn't think, he'll say "Indeed. If I can get any value,
>it must be rubbish". But if he's a logical person and thinks for a few
>minutes, he'll say "It's unfair to run that choose_a_hit_ratio program
>to get an arbitrary hit ratio and say the method is wrong, because you
>can use the same logic to write a program to get an arbitrary library
>cache hit ratio, OS in-core inode cache hit ratio or directory name
>cache hit..."
>
>My last message is not meant to revive the outdated and probably never
>correct tuning method. Instead it's meant to let oracle-l members know
>that when you need to convince those DBAs that still use that method,
>you need to accuse the BCHR method for correct reason, namely, BCHR does
>not contain sufficient information for tuning, not because you can raise
>its value by constantly scanning a table in Oracle; you won't be able to
>convince some stubbon DBAs who enjoy thinking in a quiet place.
>
>I agree that "It's not the ratio that needs condemning, it's the advice
>about..." What I disagree is the wrong educational tool people on public
>forums have recently used again and again to show the inadequacy of the
>BCHR tuning method.
>
>Yong Huang
>
>__________________________________
>Do you Yahoo!?
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>
>

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