Oracle性能调优过程中如何观察缓存命中率

在Oracle数据库性能调优的过程中，当需要观察缓存命中率(Measure the Buffer Cache Hit Ratio)时，我们可以使用下面的语句:

rem-------------------------------------------

rem 测量缓存命中率

rem ------------------------------------------

-- 获取初始缓存命中率...

SELECT ROUND((1-(phy.value / (cur.value + con.value)))*100,2) "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'

/

-- 我们人为来增加缓存命中率...

DECLARE

v_dummy dual.dummy%TYPE;

BEGIN

FOR I IN 1..1000 LOOP

SELECT dummy INTO v_dummy FROM dual;

END LOOP;

END;

/

-- 我们再来测量...

SELECT ROUND((1-(phy.value / (cur.value + con.value)))*100,2) "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'

/