cache hit ratio

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;