-- The hit ratio is a Oracle database block buffer index used in -- tuning database buffer. It is expressed as a percentage. -- Hit Ratio = -- 100*(1-("physical reads"/("db block gets" + "consistent gets"))) -- -- This value should be typically close to 100% WITH q_read AS ( SELECT CAST(name AS VARCHAR2(20)) phy_read, value read_val FROM v$sysstat WHERE name = 'physical reads' ), q_dbg AS ( SELECT CAST(name AS VARCHAR2(20)) db_block_get, value dbg_val FROM v$sysstat WHERE name = 'db block gets' ), q_cg AS ( SELECT CAST(name AS VARCHAR2(20)) consistent_get, value cg_val FROM v$sysstat WHERE name = 'consistent gets' ) SELECT phy_read, read_val, db_block_get, dbg_val, consistent_get, cg_val, 100*(1-read_val/(dbg_val+cg_val)) hit_ratio FROM q_read, q_dbg, q_cg ; Hit Ratio Query Output -- Query to calculate statistics of the Buffer Cache Hit Ratio -- from v$sysstat SELECT CAST(name AS VARCHAR2(30)) name, value FROM v$sysstat WHERE name IN ( 'db block gets from cache', 'consistent gets from cache', 'physical reads cache' ); -- Query to analyze/calculate the buffer cache hit ratio using -- v$buffer_pool_statistics SELECT name, (1-(physical_reads/(db_block_gets + consistent_gets)))* 100 Hit_ratio FROM v$buffer_pool_statistics ; -- Query to get predicted I/O for default buffer pool from -- V$DB_CACHE_ADVICE SELECT size_for_estimate size_4_estmt, buffers_for_estimate buffer_4_estmt, estd_physical_read_factor estd_phy_read_factor, estd_physical_reads esdt_phy_reads FROM V$DB_CACHE_ADVICE WHERE block_size = (SELECT value FROM V$PARAMETER WHERE name = 'db_block_size') AND name = 'DEFAULT' AND advice_status = 'ON'; v$DB_Cache_Advice Default Output -- Query to get predicted I/O for the "KEEP" pool from -- V$DB_CACHE_ADVICE SELECT size_for_estimate size_4_estmt, buffers_for_estimate buffer_4_estmt, estd_physical_read_factor estd_phy_read_factor, estd_physical_reads esdt_phy_reads FROM V$DB_CACHE_ADVICE WHERE block_size = (SELECT value FROM V$PARAMETER WHERE name = 'db_block_size') AND name = 'KEEP' AND advice_status = 'ON';
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