查找bad sql的方法

冷不防 2022-01-15 07:15 168阅读 0赞

查找bad sql的方法

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:

column sql\_text format a80;  
\-- 值得怀疑的SQL 来自[http://www.ixora.com.au/][http_www.ixora.com.au]  
select  
  substr(to\_char(s.pct, '99.00'), 2) '%'  load,  
  s.executions  executes,  
  p.sql\_text  
from  
  (  
    select  
      address,  
      disk\_reads,  
      executions,  
      pct,  
      rank() over (order by disk\_reads desc)  ranking  
    from  
      (  
        select  
          address,  
          disk\_reads,  
          executions,  
          100 \* ratio\_to\_report(disk\_reads) over ()  pct  
        from  
          sys.v\_$sql  
        where  
          command\_type != 47  
      )  
    where  
      disk\_reads > 50 \* executions  
  )  s,  
  sys.v\_$sqltext  p  
where  
  s.ranking <= 5 and  
  p.address = s.address  
order by  
  1, s.address, p.piece  
/

\-- 逻辑读多的SQL  
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;

[http_www.ixora.com.au]: http://www.ixora.com.au/