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小編給大家分享一下Oracle如何調(diào)優(yōu)相關(guān)的命中率、使用率,希望大家閱讀完這篇文章之后都有所收獲,下面讓我們一起去探討吧!
http://www.ecdoer.com/post/oracle-radio.html
計(jì)算公式:Library Cache Hit Ratio = sum(pinhits) / sum(pins)
SELECT SUM(pinhits) / sum(pins) FROM V$LIBRARYCACHE;
通常在98%以上,否則,需要要考慮加大共享池,綁定變量,修改cursor_sharing等參數(shù)。
SELECT (1 - ROUND(BYTES / (&TSP_IN_M * 1024 * 1024), 2)) * 100 || '%'
FROM V$SGASTAT
WHERE NAME = 'free memory'
AND POOL = 'shared pool';
其中: &TSP_IN_M是你的總的共享池的SIZE(M)
共享池內(nèi)存使用率,應(yīng)該穩(wěn)定在75%-90%間,太小浪費(fèi)內(nèi)存,太大則內(nèi)存不足。
查詢空閑的共享池內(nèi)存:
SELECT * FROM V$SGASTAT
WHERE NAME = 'free memory'
AND POOL = 'shared pool';
計(jì)算公式:Hit ratio = 1 - [physical reads/(block gets + consistent gets)]
SELECT NAME,
PHYSICAL_READS,
DB_BLOCK_GETS,
CONSISTENT_GETS,
1 - (PHYSICAL_READS / (DB_BLOCK_GETS + CONSISTENT_GETS)) "Hit Ratio"
FROM V$BUFFER_POOL_STATISTICS
WHERE NAME = 'DEFAULT';
通常應(yīng)在90%以上,否則,需要調(diào)整,加大DB_CACHE_SIZE。
另外一種計(jì)算命中率的方法:
命中率的計(jì)算公式為:
Hit Ratio = 1 - ((physical reads - physical reads direct - physical reads direct (lob)) / (db block gets+ consistent gets - physical reads direct - physical reads direct (lob))
分別代入上一查詢中的結(jié)果值,就得出了Buffer cache的命中率
SELECT NAME, VALUE
FROM V$SYSSTAT
WHERE NAME IN ('session logical reads',
'physical reads',
'physical reads direct',
'physical reads direct (lob)',
'db block gets',
'consistent gets');
select value from v$sysstat where name ='physical reads';
select value from v$sysstat where name ='physical reads direct';
select value from v$sysstat where name ='physical reads direct (lob)';
select value from v$sysstat where name ='consistent gets';
select value from v$sysstat where name = 'db block gets';
這里命中率的計(jì)算應(yīng)該是令 x = physical reads direct + physical reads direct (lob)
命中率 =100 - ( physical reads - x) / (consistent gets + db block gets - x)*100
通常如果發(fā)現(xiàn)命中率低于90%,則應(yīng)該調(diào)整應(yīng)用可可以考慮是否增大數(shù)據(jù)緩沖區(qū)
select sum(pinhits - reloads) / sum(pins) * 100 "hit radio" from v$librarycache;
假如共享池的命中率低于95%,就要考慮調(diào)整應(yīng)用(通常是沒使用bind var )或者增加內(nèi)存
計(jì)算CPU消耗首先要借助Linux的TOP命令尋找CPU使用量高的session,找到高占用的PID。然后借助v$process的addr字段跟v$session的paddr找到sql_id、hash_value,然后結(jié)合v$sqltext然后找相應(yīng)的SQL語句,找到之后分析執(zhí)行計(jì)劃,進(jìn)行相應(yīng)調(diào)優(yōu)。
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