If the buffer cache is too smalll for your system,
you will see "free buffer waits" in the v$system_event table. And that is the better place to check.
1.You observe that a database performance has degraded over
a period of time. While investigating the reason, you find the size of
the database buffer cache is not large enough to cache all the needed data
blocks. Which advisory component wold you refer to, in order todetermine
that required size of the database buffer cache?
A. Memory Advisor
B. Segment Advisor
C. SQL Tuning Advisor
D. SQL Access Advisor
E. Automatic Database Diagnostic Monitor(ADDM)
Answer: A