Re: Another Oracle "Myth"?

pharfromhome_at_hotmail.com (Geomancer) wrote:
> 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

Er, more common than what?

> 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?

I think you are missing this quote from the same paper:

"However, even this correlation is not reliable, because even extraordinary high hit ratios can be generated by databases with legitimately optimized SQL workload."

Morons can turn anything into a myth. That certainly isn't Millsap's fault.

Xho

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