Just as the architecture of the database buffer cache has changed dramatically from release to release, so too have the effectiveness of the tools Oracle supplies to assist with tuning the database buffer cache. In Oracle 7 Release 7.3, the DBA needed to be aware of two X$ tables used for SGA database block buffer tuning - the X$KCBRBH and X$KCBCBH tables. These tables are populated when the initialization parameters DB_BLOCK_LRU_EXTENDED_STATISTICS and DB_BLOCK_LRU_STATISTICS respectively are set and the instance is restarted. The X$KCBRBH table's COUNT column displays the number of additional cache hits gained by adding additional cache blocks (when summed over a contiguous interval of blocks). The X$KCBCBH table's COUNT column displays the number of lost cache hits gained by adding additional cache blocks (when summed over a contiguous interval of blocks).
This is a companion discussion topic for the original entry at https://blog.toadworld.com/Tune_the_Database_Buffer_Cache_Size