Home Database Mysql Tutorial Oracle如何查看sql的真实执行计划

Oracle如何查看sql的真实执行计划

Jun 07, 2016 pm 05:34 PM

平常我们用explan plan for,set autotrace,utlxplan等方式查看执行计划都是optimizer模拟生成的执行计划,并不完全符合oracle内部

知识普及:

1 平常我们用explan plan for,set autotrace,utlxplan等方式查看执行计划都是optimizer模拟生成的执行计划,并不完全符合Oracle内部对sql语句的执行路径。

2 v$sqlarea中放置的父游标,放置sql的sql_id和address

3 v$sql中对应v$sqlarea中的sql的子游标,address和child_number代表唯一的子游标

查询sql在数据库中实际的sql执行计划方法:

1 set autotrace on

如果语句返回的行很多,那么结果会非常庞大,,在sqlplus里边是一个困难的选择。

set autotrace traceonly  --并不能每次显示正确的执行计划,造成对sql优化的误导。

2 查询v$sql_plan是真实执行路径,但阅读比较困难。

3 使用如下语句可以查询sql的真实执行路径,并且格式化执行路径输出

set linesize 400

set pagesize 60

SELECT * FROM TABLE (SELECT DBMS_XPLAN.DISPLAY_CURSOR('a8tumy29tf0za','0') from dual);

--第一个为sql_id

--第二个为child_number

linux

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