如何查找运行在系统里的"bad sql"语句

来源：赛迪网    作者：shuijing

本文中我们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