Oracle 11.2.0.1.0下ACS测试

ewr212

   在版本11.2.0.1.0，ACS（adaptiver cursor sharing）测试的结果是：
    1. 在绑定窥探有效的情况下，使用绑定变量，在直方图准确的情况下，相同的SQL,CBO会对比之前的执行计划,以前执行过此SQL,如果第一次发现效率比以前低，第二次会重新生成执行计划。
    2. 在绑定窥探失效的情况下，使用绑定变量，CBO完全忽略直方图。
SQL> select * from v$version;
BANNER
----------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

SQL> show parameter _optimizer_adaptive_cursor_sharing;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ----------------------
_optimizer_adaptive_cursor_sharing   boolean     TRUE
SQL> show parameter _optimizer_extended_cursor_sharing;
NAME                                      TYPE        VALUE
------------------------------------   ----------- ---------------------
_optimizer_extended_cursor_sharing       string      UDO
_optimizer_extended_cursor_sharing_rel   string      SIMPLE

--制造数据
drop table test purge;
create table test(id number,name varchar2(10),descri varchar2(1000));
begin
for i in 1 .. 100000 loop
  insert into test values(i,'100',lpad('a',900,'b'));
  end loop;
  commit;
end;
/
update test set name='200' where rownum=1;
commit;
create index ind_name on TEST(name) nologging;
--由于在11.2.0.1.0版本下用dbms_stats收集直方图不准确，所以用analyze
--在Oracle 11.2.0.1.0下dbms_stats.gather_table_stats收集直方图不准
SQL> analyze table test compute statistics for table for columns name size 2;
--exec dbms_stats.gather_table_stats(user,'test',cascade => true,method_opt =>'for all columns size skewonly');
--数据分布
SQL> select name,count(1) from test group by name;
NAME         COUNT(1)
---------- ----------
100             99999
200                 1
SQL> set autotrace traceonly
SQL> select * from test where name='100';
已选择99999行。
执行计划
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      | 99999 |    86M|  2664   (1)| 00:00:38 |
|*  1 |  TABLE ACCESS FULL| TEST | 99999 |    86M|  2664   (1)| 00:00:38 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("NAME"='100')
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
      13515  consistent gets
        133  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73663  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> select * from test where name='200';
执行计划
----------------------------------------------------------
Plan hash value: 688048857
----------------------------------------------------------------------------------------
| Id  | Operation                   | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |     1 |   909 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST     |     1 |   909 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("NAME"='200')
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
       1342  bytes sent via SQL*Net to client
        337  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off
--使用绑定窥探，先使用查大部分数据的条件，可以看到两个都是全表扫描

--先看到绑定窥探是有效的
SQL> show parameter _optim_peek_user_binds;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_optim_peek_user_binds               boolean     TRUE
SQL> alter system flush shared_pool;
SQL> alter system flush buffer_cache;
SQL> var ccc varchar2(10);
SQL> exec :ccc:='100';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
已选择99999行。
统计信息
----------------------------------------------------------
        354  recursive calls
          0  db block gets
      13565  consistent gets
       6853  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73664  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          7  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0
SQL> select * from table(dbms_xplan.display_cursor(1301684711,0));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
HASH_VALUE  1301684711, child number 0
--------------------------------------
select * from test where name=:ccc
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |  2664 (100)|          |
|*  1 |  TABLE ACCESS FULL| TEST | 99999 |    86M|  2664   (1)| 00:00:38 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("NAME"=:CCC)
第一次执行:ccc:='200'
SQL> exec :ccc:='200';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       6849  consistent gets
          0  physical reads
          0  redo size
       1342  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0

第二次执行:ccc:='200'

SQL> exec :ccc:='200';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          3  consistent gets
          8  physical reads
          0  redo size
       1342  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0
1301684711            1

SQL> select * from table(dbms_xplan.display_cursor(1301684711,1));
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------
HASH_VALUE  1301684711, child number 1
--------------------------------------
select * from test where name=:ccc
Plan hash value: 688048857
----------------------------------------------------------------------------------------
| Id  | Operation                   | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST     |     1 |   909 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("NAME"=:CCC)


--使用绑定窥探，先使用查小部分数据的条件

SQL> alter system flush shared_pool;
SQL> alter system flush buffer_cache;
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
未选定行
SQL> exec :ccc:='200';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
统计信息
----------------------------------------------------------
        354  recursive calls
          0  db block gets
         54  consistent gets
         27  physical reads
          0  redo size
       1342  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          7  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0

SQL> select * from table(dbms_xplan.display_cursor(1301684711,0));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------
HASH_VALUE  1301684711, child number 0
--------------------------------------
select * from test where name=:ccc
Plan hash value: 688048857
----------------------------------------------------------------------------------------
| Id  | Operation                   | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |       |       |     2 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST     |     1 |   909 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("NAME"=:CCC)
第一次执行ccc:='100'
SQL> exec :ccc:='100';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
已选择99999行。
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      20106  consistent gets
       6884  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73664  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0
第二次执行ccc:='100'
SQL> exec :ccc:='100';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
已选择99999行。
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
      13515  consistent gets
        133  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73664  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0
1301684711            1
SQL> select * from table(dbms_xplan.display_cursor(1301684711,1));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------
HASH_VALUE  1301684711, child number 1
--------------------------------------
select * from test where name=:ccc
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |  2664 (100)|          |
|*  1 |  TABLE ACCESS FULL| TEST | 99999 |    86M|  2664   (1)| 00:00:38 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("NAME"=:CCC)

--不使用绑定窥探，先使用查小部分数据的条件

SQL> alter session set "_optim_peek_user_binds"=false;
SQL> alter system flush shared_pool;
SQL> alter system flush buffer_cache;
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
SQL> exec :ccc:='200';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
统计信息
----------------------------------------------------------
        354  recursive calls
          0  db block gets
       6899  consistent gets
       6853  physical reads
          0  redo size
       1342  bytes sent via SQL*Net to client
        338  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          7  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0
--看到是全表扫描，正确的是索引扫描
SQL> select * from table(dbms_xplan.display_cursor(1301684711,0));
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------
HASH_VALUE  1301684711, child number 0
--------------------------------------
select * from test where name=:ccc
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |  2663 (100)|          |
|*  1 |  TABLE ACCESS FULL| TEST | 50000 |    43M|  2663   (1)| 00:00:38 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("NAME"=:CCC)
SQL> exec :ccc:='100';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
已选择99999行。
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      13515  consistent gets
          0  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73664  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0

SQL> exec :ccc:='100';
SQL> set autotrace trace stat
SQL> select * from test where name=:ccc;
已选择99999行。
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      13515  consistent gets
          0  physical reads
          0  redo size
    1564422  bytes sent via SQL*Net to client
      73664  bytes received via SQL*Net from client
       6668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      99999  rows processed
SQL> set autotrace off
SQL> select hash_value, child_number from v$sql
    where sql_text = 'select * from test where name=:ccc';
HASH_VALUE CHILD_NUMBER
---------- ------------
1301684711            0