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;
