Re: Another Oracle "Myth"?

"Geomancer" <pharfromhome_at_hotmail.com> wrote in message news:cf90fb89.0311201853.126b1516_at_posting.google.com...
> Cary Millsap makes the assertion that a buffer hit ratio of > 99%
> OFTEN indicates inefficient SQL:
>
> http://www.hotsos.com/dnloads/1.Millsap2001.02.26-CacheRatio.pdf
>
> According to Mr. Millsap:
>
> "A hit ratio in excess of 99% often indicates the existence of
> extremely inefficient SQL that robs your system's LIO capacity."
>
> With 30 gigabyte data buffer becoming more common and RAM caches
> approaching 100% for small systems, I wonder if it is true that a
> 99.9% data buffer hit ratio is due to high caching of frequently
> referenced objects than some mysterous un-tuned SQL.
>
> To me, this does not make any sense, because many well-tuned systems
> benefit from additional RAM. The v$db_cache_advice view was
> introduced in 9i for this very reason.
>
> Is this another Myth, or am I missing something?

You are taking the statement a little too literally.

I quickly read the document and believe its an excellent written article. Cary seems to be trying to prove the point by introducing a certain shock value to it :)

He does not say that 99.9% hit ratio is always bad (which you seem to be interpreting). However he does seem to be saying one should NOT rely on 99.9% hit ratio to make the judgment that the database performance is good. The fact might just be the opposite. A statement which I will agree with fully.

Did I say its an excellent article!

Anurag Received on Thu Nov 20 2003 - 21:28:30 CST