Oracle Tuning And Performance Analysis

Computing the Hit Ratio

Source: http://www.oreilly.com/catalog/oracle2/chapter/ch10.html

SELECT 
   SUM(DECODE(name, 'consistent gets',value, 0))  "Consis Gets",
   SUM(DECODE(name, 'db block gets',value, 0))    "DB Blk Gets",
   SUM(DECODE(name, 'physical reads',value, 0))   "Phys Reads",
  (SUM(DECODE(name, 'consistent gets',value, 0))  
    + SUM(DECODE(name, 'db block gets',value, 0))  
    -  SUM(DECODE(name, 'physical reads',value, 0)))
    / (SUM(DECODE(name, 'consistent gets',value, 0)) 
    + SUM(DECODE(name, 'db block gets',value, 0))  )  * 100 "Hit Ratio" 
FROM v$sysstat;