本文主要介紹了如何查找運行系統裡bad sql,需要大家注意的是我們需要根據自己的實際情況來具體分析。而不應該照搬下面介紹的這些方法。當我們使用這些SQL語句時，會對系統表產生分組操作，當然也增大了系統的負載。希望大家在系統啟動了一段時間後，在半夜負載較輕的時間定時(比如:一個月)來仔細查看一下。
查找bad sql的方法:
select * from (select buffer_gets, sql_text
from v$sqlarea
where buffer_gets >500000
order by buffer_gets desc) where rownum<=30;
執行次數多的SQL：
select sql_text,executions from
(select sql_text,executions from
v$sqlarea order by executions desc)
where rownum<81;
讀硬盤多的SQL：
select sql_text,disk_reads from
(select sql_text,disk_reads from v$sqlarea order by disk_reads desc)
where rownum<21;
排序多的SQL：
select sql_text,sorts from
(select sql_text,sorts from v$sqlarea order by sorts desc)
where rownum<21;
分析的次數太多，執行的次數太少，要用綁變量的方法來寫sql:
set pagesize 600;
set linesize 120;
select substr(sql_text,1,80) "sql", count(*), sum(executions) "totexecs"
from v$sqlarea
where executions < 5
group by substr(sql_text,1,80)
having count(*) > 30
order by 2;
游標的觀察：
set pages 300;
select sum(a.value), b.name
from v$sesstat a, v$statname b
where a.statistic# = b.statistic#
and b.name = 'opened cursors current'
group by b.name;
select count(0) from v$open_cursor;
select user_name,sql_text,count(0) from v$open_cursor
group by user_name,sql_text having count(0)>30;
查看當前用戶&username執行的SQL：
select sql_text from v$sqltext_with_newlines
where (hash_value,address) in
(select sql_hash_value,sql_address from
v$session where username='&username')
order by address,piece;
