Re: Another Oracle "Myth"?

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 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?

There are systems out there that genuinely require high frequency access to a small set of data - thus resulting in a 99.9% cache usage.

(In my opinion) there are a far greater number of systems out there that needlessly waste CPU by excessively pounding away at objects resulting in a 99.9% cache usage.

hth
connor Received on Fri Nov 21 2003 - 05:48:51 CST