Oracle 中定位重要(消耗資源多)的SQL

在分析SQL效能的時候，經常需要確定資源消耗多的SQL，總結如下：

1 查看值得懷疑的SQL
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;

2 查看消耗記憶體多的sql

select b.username ,a.buffer_gets ,a.executions,

       a.disk_reads/decode(a.executions,0,1,a.executions),a.sql_text SQL

from v$sqlarea a,dba_users b

where a.parsing_user_id = b.user_id

 and a.disk_reads >10000

order by disk_reads desc;

3 查看邏輯讀多的SQL
select*

from(select buffer_gets, sql_text

     from v$sqlarea

     where buffer_gets>500000

     order by buffer_gets desc)

where rownum<=30;

4 查看執行次數多的SQL

select sql_text, executions

from(select sql_text, executions from v$sqlarea order by executions desc)

where rownum<81;

5 查看讀硬碟多的SQL

select sql_text, disk_reads

from(select sql_text, disk_reads from v$sqlarea order by disk_reads desc)

where rownum<21;

6 查看排序多的SQL

select sql_text, sorts

from(select sql_text, sorts from v$sqlarea order by sorts desc)

where rownum<21;

7 分析的次數太多，執行的次數太少，要用綁變數的方法來寫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;

8 遊標的觀察
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;

9 查看目前使用者&username執行的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;