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Home -> Community -> Mailing Lists -> Oracle-L -> Correct way to accuse BCHR tuning method (Was: Hit ratio)
[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My last message is not meant to revive the outdated and probably never correct tuning method.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
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