Dictionary Cache Hit Ratio
The dictionary hit ratio displays the percentage of memory reads for the data dictionary and other objects.
Query for dictionary hit ratio
SQL>select (1-(sum(getmisses)/sum(gets))) * 100 "Hit Ratio" from v$rowcache
Library Cache Hit Ratio
The library cache hit ratio reveals the percentage of memory reads for actual statements and PL/SQL objects. Note that a high hit ratio is not always good; see Chapter 4 for a detailed explanation.
Query for library hit ratio
select Sum(Pins) / (Sum(Pins) + Sum(Reloads)) * 100 "Hit Ratio"