USER HIT RATIO: -
Username - Name of the user
Consistent Gets - The number of accesses made to the block buffer to retrieve data in a consistent mode.
DB Blk Gets - The number of blocks accessed via single block gets (i.e. not through the consistent get mechanism).
Physical Reads - The cumulative number of blocks read from disk.
Logical reads are the sum of consistent gets and db block gets.
The db block gets statistic value is incremented when a block is read for update and when segment header blocks are accessed.
Hit ratio should be > 90%
((CONSISTENT_GETS+BLOCK_GETS-PHYSICAL_READS) / (CONSISTENT_GETS+BLOCK_GETS)) Ratio
from v$session, v$sess_io
where v$session.SID = v$sess_io.SID
and (CONSISTENT_GETS+BLOCK_GETS) > 0
and USERNAME is not null