Database Buffer Cache should be sufficiently large to accommodate the blocks that are frequently and repeatedly used. However, it should not be excessively large to the extent that it accommodates blocks that are only used once.

Generally, a database administrator can use the Database Buffer Cache Advisor to help determine the optimal size for the Database Buffer Cache. However, to properly use the advisor, the STATISTIC_LEVEL parameter must be set to either ALL or TYPICAL.

The Database Buffer Cache Advisor can be accessed through V$DB_CACHE_ADVICE or via the Enterprise Manager.