ORACLE如何查找运行系统里可能有问题的sql

最新推荐文章于 2021-04-09 22:04:58 发布

java_hai_147

最新推荐文章于 2021-04-09 22:04:58 发布

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分类专栏： pl/sql

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本文介绍了一系列用于Oracle数据库SQL性能调优的方法，包括查找执行次数多、读硬盘多及排序多的SQL语句，同时提供了分析SQL执行效率低下的原因及改进措施。

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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<=10;

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<10;

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<10;

排序多的SQL：
select sql_text,sorts from
(select sql_text,sorts from v$sqlarea order by sorts desc)
where rownum<10;

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 1000;
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 100;
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)>40;

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;