Hit Ratios

free memory in shared pool:
select * from v$sgastat
where name='free memory'
and pool='shared pool'

Library cache hit ratio:
select sum(pinhits)/sum(pins) from v$librarycache

Dictionary cache hit ratio:
select (sum(gets-getmisses-fixed))/sum(gets)"row cache" from v$rowcache


select parameter,sum(gets),sum(getmisses),100*sum(gets-getmisses)/sum(gets) pct_succ_gets,sum(modifications) updates
from v$rowcache
where gets>0
group by parameter