Buffer Cache Hit Ratio ================= What means this difference of cache hit ratio: SELECT 1 -(phy.value / (cur.value + con.value)) "CACHE HIT RATIO" FROM v$sysstat cur, v$sysstat con, v$sysstat phy WHERE cur.name = 'db block gets' AND con.name = 'consistent gets' AND phy.name = 'physical reads' / CACHE HIT RATIO --------------- .993579918 SELECT name, 1-(physical_reads / (db_block_gets + consistent_gets)) "HIT_RATIO" FROM v$buffer_pool_statistics / NAME HIT_RATIO ------------------------------ ---------- KEEP .999882139 DEFAULT .687961184 Thanks Followup: one shows overall hit. the other shows the hit by buffer pool.