本文主要介绍了如何查找运行系统里bad sql,需要大家注意的是我们需要根据自己的实际情况来具体分析。而不应该照搬下面介绍的这些方法。当我们使用这些SQL语句时，会对系统表产生分组操作，当然也增大了系统的负载。希望大家在系统启动了一段时间后，在半夜负载较轻的时间定时(比如:一个月)来仔细查看一下。

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;
 
执行次数多的SQL：

select sql_text,executions from
(select sql_text,executions from
v$sqlarea order by executions desc)
where rownum<81;
 
读硬盘多的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;
 
分析的次数太多，执行的次数太少，要用绑变量的方法来写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;
 
游标的观察：

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;
 
查看当前用户&username执行的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;