Dataabse hit ratios

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"
from V$LibraryCache