Another Oracle "Myth"?

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? Received on Thu Nov 20 2003 - 20:53:02 CST