Oracle 锁定临时表统计信息及锁住后是否能用动态采集的hint

全局临时表的统计信息是不能被收集的，如果被收集，它的统计信息肯定为0，会造成执行计划不准，所以要锁定它的统计信息，禁止系统自动收集。

--先解锁表的统计信息，然后删除表的统计信息，最后锁住表的统计信息

declare

  v_sqlvarchar2(500);

  cursor rowList1 is

  select'begin dbms_stats.unlock_table_stats(user,''' || table_name ||'''); end;'

    from user_tables s

  where s.temporary = 'Y'; 

  cursor rowList2 is

  select'begin dbms_stats.delete_table_stats(user,''' || table_name ||'''); end;'

    from user_tables s

  where s.temporary = 'Y';

  cursor rowList3 is

  select'begin dbms_stats.lock_table_stats(user,''' || table_name ||'''); end;'

    from user_tables s

  where s.temporary = 'Y'; 

begin

  open rowList1;

  open rowList2;

  open rowList3;

  loop

    fetch rowList1  into v_sql;

      executeimmediate v_sql;

    exitwhen rowList1%notfound;

  endloop;

  loop

    fetch rowList2  into v_sql;

      executeimmediate v_sql;

    exitwhen rowList2%notfound;

  endloop;

  loop

    fetch rowList3  into v_sql;

      executeimmediate v_sql;

    exitwhen rowList3%notfound;

  endloop; 

  close rowList1;

  close rowList2;

  close rowList3;

end;

-- STATTYPE_LOCKED='ALL'意思是表的统计信息被锁

select s.table_name,s.STATTYPE_LOCKED  from user_TAB_STATISTICS s  where s.STATTYPE_LOCKED='ALL';

--当表的统计信息被锁后，用动态采集的hint是否生效，实验结果是hint是生效的

SQL> drop table test purge;
SQL> create table test as select * from dba_objects;
SQL> exec dbms_stats.lock_table_stats(user,'test');
SQL> select s.num_rows, s.last_analyzed
      from user_tables s
    where s.table_name = 'TEST';
  NUM_ROWS LAST_ANALYZED
---------- --------------

--说明表被锁了
SQL> select s.STATTYPE_LOCKED from user_TAB_STATISTICS s
    where s.table_name='TEST';
STATTYPE_L
----------
ALL
SQL> select count(*) from test;
  COUNT(*)
----------
    70384
SQL> set autotrace traceonly
SQL> select /*+ dynamic_sampling(test 1) */ * from test;
已选择70384行。
执行计划
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time    |
--------------------------------------------------------------------------
|  0 | SELECT STATEMENT  |      |  160K|    31M|  199  (3)| 00:00:03 |
|  1 |  TABLE ACCESS FULL| TEST |  160K|    31M|  199  (3)| 00:00:03 |
--------------------------------------------------------------------------
Note
-----
  - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          4  recursive calls
          0  db block gets
      5239  consistent gets
          0  physical reads
          0  redo size
    3186713  bytes sent via SQL*Net to client
      51949  bytes received via SQL*Net from client
      4694  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      70384  rows processed

SQL> select /*+ dynamic_sampling(test 5) */ * from test;
已选择70384行。
执行计划
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time    |
--------------------------------------------------------------------------
|  0 | SELECT STATEMENT  |      |  9747 |  1970K|  195  (0)| 00:00:03 |
|  1 |  TABLE ACCESS FULL| TEST |  9747 |  1970K|  195  (0)| 00:00:03 |
--------------------------------------------------------------------------
Note
-----
  - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          4  recursive calls
          0  db block gets
      5239  consistent gets
          0  physical reads
          0  redo size
    3186713  bytes sent via SQL*Net to client
      51949  bytes received via SQL*Net from client
      4694  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      70384  rows processed

SQL> select /*+ dynamic_sampling(test 10) */ * from test;
已选择70384行。
执行计划
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation        | Name | Rows  | Bytes | Cost (%CPU)| Time    |
--------------------------------------------------------------------------
|  0 | SELECT STATEMENT  |      | 70384 |    13M|  197  (2)| 00:00:03 |
|  1 |  TABLE ACCESS FULL| TEST | 70384 |    13M|  197  (2)| 00:00:03 |
--------------------------------------------------------------------------
Note
-----
  - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      5165  consistent gets
          0  physical reads
          0  redo size
    3186713  bytes sent via SQL*Net to client
      51949  bytes received via SQL*Net from client
      4694  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      70384  rows processed