Oracle 利用10053处理不走索引语句一则

语句：

select count(1) from DW_PAGE_VIEW_FACT a where a.cookie_id='dd2a760b704e3936';

执行计划：

SQL> explain plan for select count(1) from DW_PAGE_VIEW_FACT a where a.cookie_id='dd2a760b704e3936';

Explained.

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
Plan hash value: 53213563

-----------------------------------------------------------------------------------------------
| Id  | Operation      | Name   | Rows  | Bytes | Cost (%CPU)| Time  | Pstart| Pstop |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |    |     1 |    17 | 37862   (1)| 00:07:35 |  |  |
|   1 |  SORT AGGREGATE      |    |     1 |    17 |       |   |  |  |
|   2 |   PARTITION RANGE ALL|    |    12 |   204 | 37862   (1)| 00:07:35 |     1 |   630 |
|*  3 |    TABLE ACCESS FULL | DW_PAGE_VIEW_FACT |    12 |   204 | 37862   (1)| 00:07:35 |     1 |   630 |
-----------------------------------------------------------------------------------------------
PLAN_TABLE_OUTPUT
---------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------

3 - filter("A"."COOKIE_ID"='dd2a760b704e3936')

15 rows selected.

可以看到虽然通过cookie_id查找，但仍然走的全表扫描，看下表上索引的情况

SQL> select index_name,table_name,column_name from dba_ind_columns where table_name='DW_PAGE_VIEW_FACT';

INDEX_NAME     TABLE_NAME          COLUMN_NAM
--------------- -------------------- ----------
IND_PAGE_VIEW   DW_PAGE_VIEW_FACT    SESSION_ID
IDX_PAGE_COOKIE DW_PAGE_VIEW_FACT    COOKIE_ID

设置10053跟踪计划生成

SQL> alter session set events '10053 trace name context forever,level 1';
Session altered.

SQL> select count(1) from zybi.DW_PAGE_VIEW_FACT a where a.cookie_id='dd2a760b704e3936';
COUNT(1)
----------
26
SQL> alter session set events '10053 trace name context off';
Session altered.

查看跟踪文件：

***************************************

BASE STATISTICAL INFORMATION

***********************

Table Stats::

  Table: DW_PAGE_VIEW_FACT  Alias:  A  (Using composite stats)

    #Rows: 4141249  #Blks:  139516  AvgRowLen:  223.00

Index Stats::
  Index: IDX_PAGE_COOKIE  Col#: 8

    LVLS: 2  #LB: 14804  #DK: 258768  LB/K: 1.00  DB/K: 1.00  CLUF: 515320.00

    UNUSABLE

  Index: IND_PAGE_VIEW  Col#: 10

    USING COMPOSITE STATS

    LVLS: 2  #LB: 36272  #DK: 448128  LB/K: 1.00  DB/K: 1.00  CLUF: 281753.00

Access path analysis for DW_PAGE_VIEW_FACT

***************************************

SINGLE TABLE ACCESS PATH

  Single Table Cardinality Estimation for DW_PAGE_VIEW_FACT[A]

  Column (#8):

    NewDensity:0.000003, OldDensity:0.000133 BktCnt:254, PopBktCnt:30, PopValCnt:1, NDV:291648

  Table: DW_PAGE_VIEW_FACT  Alias: A

    Card: Original: 4141249.000000  Rounded: 13  Computed: 12.52  Non Adjusted: 12.52

  Access Path: TableScan

    Cost:  37862.32  Resp: 37862.32  Degree: 0

      Cost_io: 37787.00  Cost_cpu: 2401579483

      Resp_io: 37787.00  Resp_cpu: 2401579483
  Best:: AccessPath: TableScan

         Cost: 37862.32  Degree: 1  Resp: 37862.32  Card: 12.52  Bytes: 0

***************************************

很不幸IDX_PAGE_COOKIE处于UNUSABLE状态，当前库之所以关于该表的语句能正常执行，是因为skip_unusable_indexes=true，

修改后会报错：

SQL> insert into zybi.DW_PAGE_VIEW_FACT select * from zybi.DW_PAGE_VIEW_FACT where rownum=1;
insert into zybi.DW_PAGE_VIEW_FACT select * from zybi.DW_PAGE_VIEW_FACT where rownum=1
*
ERROR at line 1:
ORA-01502: index 'ZYBI.IDX_PAGE_COOKIE' or partition of such index is in
unusable state

这个索引失效很可能是移动表或表压缩造成的，需要重建索引：

SQL> alter index zybi.IDX_PAGE_COOKIE rebuild;

Index altered.

SQL> select degree from dba_indexes where index_name='IDX_PAGE_COOKIE';

DEGREE
------------------------------
1

再次查看执行计划：

 

SQL>  explain plan for select count(1) from zybi.DW_PAGE_VIEW_FACT a where a.cookie_id='dd2a760b704e3936';

Explained.

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------
Plan hash value: 3653499665

------------------------------------------------------------------------------
| Id  | Operation   | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |   1 |  17 |   3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE   |      |   1 |  17 |   |     |
|*  2 |   INDEX RANGE SCAN| IDX_PAGE_COOKIE |  12 | 204 |   3   (0)| 00:00:01 |
------------------------------------------------------------------------------

Predicate Information (identified by operation id):

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------

2 - access("A"."COOKIE_ID"='dd2a760b704e3936')

14 rows selected.