Query to find current cache hit ratio in database
Below query represents the exact cache hit ratio happening currently in database
The minimum figure of 89% is quoted below, but depending on the type of environment this need to be changed.
PROMPT
PROMPT Hit ratio should exceed 89%
SELECT Sum(Decode(a.name, 'consistent gets', a.value, 0)) "Consistent Gets",
Sum(Decode(a.name, 'db block gets', a.value, 0)) "DB Block Gets",
Sum(Decode(a.name, 'physical reads', a.value, 0)) "Physical Reads",
Round(((Sum(Decode(a.name, 'consistent gets', a.value, 0)) +
Sum(Decode(a.name, 'db block gets', a.value, 0)) -
Sum(Decode(a.name, 'physical reads', a.value, 0)) )/
(Sum(Decode(a.name, 'consistent gets', a.value, 0)) +
Sum(Decode(a.name, 'db block gets', a.value, 0))))
*100,2) "Hit Ratio %"
FROM v$sysstat a;