可愛的週六日又到了,今天分享一份珍藏的筆記,關於Oracle中各個命中率的計算以及相關的調優。
1)Library Cache的命中率:
.計算公式:Library Cache Hit Ratio = sum(pinhits) / sum(pins)
SQL>SELECT SUM(pinhits)/sum(pins) FROM V$LIBRARYCACHE;
通常在98%以上,否則,需要要考慮加大共享池,綁定變量,修改cursor_sharing等參數。
2)計算共享池內存使用率:
SQL>SELECT (1 - ROUND(BYTES / (&TSP_IN_M * 1024 * 1024), 2)) * 100 || '%'
FROM V$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)
共享池內存使用率,應該穩定在75%-90%間,太小浪費內存,太大則內存不足。
查詢空閒的共享池內存:
SQL>SELECT * FROM V$SGASTAT
WHERE NAME = 'free memory' AND POOL = 'shared pool';
3)db buffer cache命中率:
計算公式:Hit ratio = 1 - [physical reads/(block gets + consistent gets)]
SQL>SELECT NAME, PHYSICAL_READS, DB_BLOCK_GETS, CONSISTENT_GETS,
1 - (PHYSICAL_READS / (DB_BLOCK_GETS + CONSISTENT_GETS)) "Hit Ratio"
FROM V$BUFFER_POOL_STATISTICS
WHERE NAME='DEFAULT';
通常應在90%以上,否則,需要調整,加大DB_CACHE_SIZE
4)數據緩衝區命中率:
SQL> select value from v$sysstat where name ='physical reads';
SQL> select value from v$sysstat where name ='physical reads direct';
SQL> select value from v$sysstat where name ='physical reads direct (lob)';
SQL> select value from v$sysstat where name ='consistent gets';
SQL> select value from v$sysstat where name = 'db block gets';
這裡命中率的計算應該是
令 x = physical reads direct + physical reads direct (lob)
命中率 =100 - ( physical reads - x) / (consistent gets + db block gets - x)*100
通常如果發現命中率低於90%,則應該調整應用可可以考慮是否增大數據緩衝區
5)共享池的命中率:
SQL> select sum(pinhits-reloads)/sum(pins)*100 "hit radio" from v$librarycache;
假如共享池的命中率低於95%,就要考慮調整應用(通常是沒使用bind var )或者增加內存
6)計算在內存中排序的比率:
SQL>SELECT * FROM v$sysstat t WHERE NAME='sorts (memory)';—查詢內存排序數
SQL>SELECT * FROM v$sysstat t WHERE NAME='sorts (disk)';—查詢磁盤排序數
--caculate sort in memory ratio
SQL>SELECT round(&sort_in_memory/(&sort_in_memory+&sort_in_disk),4)*100||'%' FROM dual;
此比率越大越好,太小整要考慮調整,加大PGA
7)PGA的命中率:
計算公式:BP x 100 / (BP + EBP)
BP: bytes processed
EBP: extra bytes read/written
SQL>SELECT * FROM V$PGASTAT WHERE NAME='cache hit percentage';
或者從OEM的圖形界面中查看
我們可以查看一個視圖以獲取Oracle的建議值:
8)共享區字典緩存區命中率
計算公式:SUM(gets - getmisses - usage -fixed) / SUM(gets)
命中率應大於0.85
SQL>select sum(gets-getmisses-usage-fixed)/sum(gets) from v$rowcache;
9)數據高速緩存區命中率
計算公式:
1-(physical reads / (db block gets + consistent gets))命中率應大於0.90最好
SQL>select name,value from v$sysstat where name in ('physical reads','db block gets','consistent gets');
10)共享區庫緩存區命中率
計算公式:SUM(pins - reloads) / SUM(pins)
命中率應大於0.99
SQL>select sum(pins-reloads)/sum(pins) from v$librarycache;
11)檢測回滾段的爭用
SUM(waits)值應小於SUM(gets)值的1%
SQL>select sum(gets),sum(waits),sum(waits)/sum(gets) from v$rollstat;
12)檢測回滾段收縮次數
SQL>select name,shrinks from v$rollstat, v$rollname where v$rollstat.usn = v$rollname.usn;
覺得有用的幫忙轉發下哦~
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