Why a 99%+ Database Buffer Cache Hit Ratio is Not Ok
Many tuning professionals and textbook authors sell advice encouraging their customers to enjoy the performancevirtues of Oracle database buffer cache hit ratios that approach 100%. However, database buffer cache hit ratio is
not a reliable system performance metric. Buffer cache hit ratios above 99% usually indicate particularly serious
SQL inefficiencies. Repairs of these inefficiencies often yield 100× or greater performance improvements, yet the
optimizations result in reduced database buffer cache hit ratios. This paper shows why a 99%+ buffer cache hit ratio
almost always signals performance inefficiencies, including real-life examples. It shows how to detect the
inefficiencies and how to repair them. It concludes with recommendations about what metrics the performance
analyst should use instead of the venerable but unreliable database buffer cache hit ratio.
Well，this essay will show u the tricky side.
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