在分析SQL性能的时候，经常需要确定资源消耗多的SQL，总结如下：
1 查看值得怀疑的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 查看消耗内存多的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;
4 查看执行次数多的SQL
select sql_text, executions
from (select sql_text, executions from v$sqlarea order by executions desc)
where rownum < 81;
5 查看读硬盘多的SQL
select sql_text, disk_reads
from (select sql_text, disk_reads from v$sqlarea order by disk_reads desc)
where rownum < 21;
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;
8 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;
9 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;