v$sql中的executions以多长时间来计算的？

v$sql中的executions以多长时间来计算的？

如题，执行次数(executions)是从数据库启动后就开始计算的，还是只是最近几个小时的执行次数？能清除v$sql里面的信息重新来过吗？

http://www.itpub.net/thread-959103-1-1.html

SQL> create table test as select * from dba_objects;

表已创建。

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> select EXECUTIONS
  2   from v$sql where sql_text='select count(*) from test';

EXECUTIONS
----------
         1

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> select EXECUTIONS
  2   from v$sql where sql_text='select count(*) from test';

EXECUTIONS
----------
         2

SQL>  select count(*) from test;

  COUNT(*)
----------
     50437

SQL>  select EXECUTIONS
  2    from v$sql where sql_text='select count(*) from test';

EXECUTIONS
----------
         2

SQL> grant select on test to scott;　　//invalidation cursor

授权成功。

SQL> select EXECUTIONS
  2   from v$sql where sql_text='select count(*) from test';

未选定行

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> select EXECUTIONS
  2   from v$sql where sql_text='select count(*) from test';

EXECUTIONS
----------
         1

一个小测试

SQL> alter system flush shared_pool;

系统已更改。

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> /

  COUNT(*)
----------
     50437

SQL> alter session set optimizer_mode=rule;　//产生新version
会话已更改。

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> /

  COUNT(*)
----------
     50437

SQL> alter session set optimizer_mode=choose;　//产生新version


会话已更改。

SQL> select count(*) from test;

  COUNT(*)
----------
     50437

SQL> select child_number,executions from v$sql where sql_text='select count(*) from test';

CHILD_NUMBER EXECUTIONS
------------ ----------
           0          2
           1          2
           2          1

SQL> select sql_id from v$sql where sql_text='select count(*) from test';

SQL_ID
-------------
7b2twsn8vgfsc
7b2twsn8vgfsc
7b2twsn8vgfsc

SQL> select * from v$sql_shared_cursor where sql_id='7b2twsn8vgfsc';

SQL_ID        ADDRESS  CHILD_AD CHILD_NUMBER U S O O S L S E B P I S T A B D L T
------------- -------- -------- ------------ - - - - - - - - - - - - - - - - - -
R I I R L I O S M U T N F A I T D L D B P C S R P T M B M R O P M F L
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
7b2twsn8vgfsc 1F5CA95C 226E0CB8            0 N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N

7b2twsn8vgfsc 1F5CA95C 226DEFA8            1 N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N Y N N N N

7b2twsn8vgfsc 1F5CA95C 226DABD8            2 N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N Y N N N N  

查文档倒数第５个
OPTIMIZER_MODE_MISMATCH VARCHAR2(1) Parameter OPTIMIZER_MODE mismatch (for example, all_rows versus first_rows_1)