How can we increase the buffer cache hit ratio. Can anybody let me know how to do this ? Thank you.
You could use Connor McDonald's script that allows you to select any Buffer Cache Hit Ratio you like: http://www.oracledba.co.uk/tips/choose.htm
Note... that's a somewhat facetious answer, but illustrates an important point, that tuning based on BCHR is misleading. An inefficient query that hits the same block repeatedly but unnecessarily would show up as being more efficient than one that only hit it once.
I'd recommend using a query tuning approach of reducing logical IOs. See "Optimizing Oracle Performance" by Millsap and Holt for good coverage of the subject.
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