????4????????????Ч??

--?????????????
a????????????????
scott@ORA11G> @idx_info
Enter value for owner: scott
Enter value for table_name: big_table

Table Name                Index Name                CL_NAM    CL_POS Status   IDX_TYP         DSCD
------------------------- ------------------------- --------- ------ -------- --------------- ----
BIG_TABLE                 BIG_TABLE_PK              ID             1 VALID    NORMAL          ASC

scott@ORA11G> @idx_stat
Enter value for input_table_name: big_table
Enter value for owner: scott

                                                     AVG LEAF BLKS AVG DATA BLKS
BLEV IDX_NAME        LEAF_BLKS   DST_KEYS       PER KEY       PER KEY CLUST_FACT LAST_ANALYZED         TB_BLKS    TB_ROWS
---- -------------- ---------- ---------- ------------- ------------- ---------- ------------------ ---------- ----------
   1 BIG_TABLE_PK          208     100000             1             1       1483 20130524 10:45:51        1515     100000

--????????????
scott@ORA11G> show parameter optimizer_index_

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
optimizer_index_caching              integer     0
optimizer_index_cost_adj             integer     100
scott@ORA11G> show parameter optimizer_mode

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode                       string      ALL_ROWS


b?????????20%?????е?????
scott@ORA11G> alter system flush buffer_cache;                                                
scott@ORA11G> select sum(object_id)??avg(object_id) from big_table where id between 20000 and 40000;

Execution Plan
----------------------------------------------------------
Plan hash value: 3098837282                             -- ??м???У????????????Χ???
---------------------------------------------------------------------------------------------
| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |              |     1 |    18 |   341   (0)| 00:00:05 |
|   1 |  SORT AGGREGATE              |              |     1 |    18 |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| BIG_TABLE    | 20046 |   352K|   341   (0)| 00:00:05 |
|*  3 |    INDEX RANGE SCAN          | BIG_TABLE_PK | 20046 |       |    43   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("ID">=20000 AND "ID"<=40000)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        351  consistent gets
        351  physical reads
          0  redo size
        427  bytes sent via SQL*Net to client
        349  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

scott@ORA11G> alter system flush buffer_cache;
scott@ORA11G> select /*+ full(big_table) */ sum(object_id)??avg(object_id) from big_table where id between 20000 and 40000;

Execution Plan
----------------------------------------------------------
Plan hash value: 599409829                ---- ??????????????????
--------------------------------------------------------------------------------
| Id  | Operation          | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |           |     1 |    18 |   413   (1)| 00:00:05 |
|   1 |  SORT AGGREGATE    |           |     1 |    18 |            |          |
|*  2 |   TABLE ACCESS FULL| BIG_TABLE | 20046 |   352K|   413   (1)| 00:00:05 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - filter("ID"<=40000 AND "ID">=20000)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       1486  consistent gets
       1484  physical reads
          0  redo size
        427  bytes sent via SQL*Net to client
        349  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

--????????????β????е?consistent gets??physical reads


c?????????30%?????е?????
scott@ORA11G> alter system flush buffer_cache;
scott@ORA11G> select sum(object_id)??avg(object_id) from big_table where id between 20000 and 50000;

Execution Plan
----------------------------------------------------------
Plan hash value: 599409829             --->???????????????????30%???????????????????????
--------------------------------------------------------------------------------
| Id  | Operation          | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |           |     1 |    18 |   413   (1)| 00:00:05 |
|   1 |  SORT AGGREGATE    |           |     1 |    18 |            |          |
|*  2 |   TABLE ACCESS FULL| BIG_TABLE | 30012 |   527K|   413   (1)| 00:00:05 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - filter("ID"<=50000 AND "ID">=20000)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       1486  consistent gets
       1484  physical reads
          0  redo size
        427  bytes sent via SQL*Net to client
        349  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

--?????????????????????????????
scott@ORA11G> alter system flush buffer_cache;
scott@ORA11G> select /*+ index(big_table big_table_pk) */ sum(object_id)??avg(object_id)
  2  from big_table where id between 20000 and 50000;

Execution Plan
----------------------------------------------------------
Plan hash value: 3098837282
---------------------------------------------------------------------------------------------
| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |              |     1 |    18 |   511   (1)| 00:00:07 |
|   1 |  SORT AGGREGATE              |              |     1 |    18 |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| BIG_TABLE    | 30012 |   527K|   511   (1)| 00:00:07 |
|*  3 |    INDEX RANGE SCAN          | BIG_TABLE_PK | 30012 |       |    64   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("ID">=20000 AND "ID"<=50000)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        526  consistent gets
        526  physical reads
          0  redo size
        427  bytes sent via SQL*Net to client
        349  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
        
--????????β???????????????????????
--????????????????????????????????????????????????30%???Oracle ???????????????
--?????????????????????????????????30%?????Σ???????????????????????????????Ч?????????????Ч??
--????????????????????????????80%????????????????????????????ж?????
--???????????????????????????????????????????????????????￡?????????????裬??????????????????Ч??
--???
--????????????????????????????????????????????????????????o??????
--??Σ????????????????????????????粻???????????????????????
--????????????????????????????н????????????в???????????в?????sum(object_id)