如何显示执行计划的真实开销?
执行计划如何显示e-rows,a-rows？
今天一个学生问我在执行计划如何显示E-rows,A-rows
通常有两种方式：
1. 加入hint:
SQL> create table daodao (a integer);
表已创建。
SQL> insert into daodao select object_idfrom dba_objects;
已创建 76167 行。
SQL> commit;
提交完成。
SQL> create index daodao_idx ondaodao(a);
索引已创建。
SQL> select /*+ gather_plan_statistics*/ * from daodao where a= 5;
A
----------
5
SQL> select * fromtable(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
SQL_ID gqtauwwjxp3tv, child number 0
-------------------------------------
select /*+ gather_plan_statistics */ * from daodao where a= 5
Plan hash value: 671796503
--------------------------------------------------------------------------------
---------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time |
Buffers |
--------------------------------------------------------------------------------
---------
| 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.01 |
3 |
|* 1| INDEX RANGE SCAN| DAODAO_IDX | 1 | 1 | 1 |00:00:00.01 |
3 |
--------------------------------------------------------------------------------
---------
Predicate Information (identified byoperation id):
---------------------------------------------------
1- access("A"=5)
Note
-----
-dynamic sampling used for this statement (level=2)；
2. 修改会话参数:
SQL> show parameter statis
optimizer_use_pending_statistics boolean FALSE
statistics_level string TYPICAL
timed_os_statistics integer 0
timed_statistics boolean TRUE
SQL> alter session setstatistics_level=all;
会话已更改。
SQL> select * from daodao where a= 5;
5
SQL> select * fromtable(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
SQL_ID autxwkucwhux6, child number 0
-------------------------------------
select * from daodao where a= 5
Plan hash value: 671796503
--------------------------------------------------------------------------------
---------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time |
Buffers |
--------------------------------------------------------------------------------
---------
| 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.01 |
3 |
|* 1| INDEX RANGE SCAN| DAODAO_IDX | 1 | 1 | 1 |00:00:00.01 |
3 |
--------------------------------------------------------------------------------
---------
Predicate Information (identified byoperation id):
---------------------------------------------------
1- access("A"=5)
Note
-----
-dynamic sampling used for this statement (level=2)
已选择22行。