select 1 - (phy.value - lob.value - dir.value) / ses.value "Cache Hit Ratio"
from v$sysstat ses, v$sysstat lob, v$sysstat dir, v$sysstat phy
where ses.name='session logical reads'
and dir.name='physical reads direct'
and lob.name= 'physical reads direct (lob)'
and phy.name='physical reads'
/

select name,physical_reads,db_block_gets,consistent_gets,
1-(physical_reads / (db_block_gets + consistent_gets)) "HITS"
from v$buffer_pool_statistics
/


결과값은 90%이상 이어야 함

90%이하면 DB_CACHE_SIZE 값을 늘려준다.