查找运行系统里低劣的SQL方法

查找运行系统里bad sql是一个古老的话题, 我们要根据自己的实际情况来分析。绝不能教条的运用下面介绍的这些方法。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。建议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(例如:一个月)来查一查。一定要具体问题具体分析。下面是我收藏的一些查找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;