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; |
