Oracle 局部前缀索引和局部非前缀索引

  局部前缀索引和局部非前缀索引是对于分区表而言的，那到底选择哪种索引呢？先做一个实验：

1.制造数据

create table TEST_P

(
  OWNER          VARCHAR2(30),
  OBJECT_NAME    VARCHAR2(128),
  SUBOBJECT_NAME VARCHAR2(30),
  OBJECT_ID      NUMBER,
  DATA_OBJECT_ID NUMBER,
  OBJECT_TYPE    VARCHAR2(19),
  CREATED        DATE,
  LAST_DDL_TIME  DATE,
  TIMESTAMP      VARCHAR2(19),
  STATUS         VARCHAR2(7),
  TEMPORARY      VARCHAR2(1),
  GENERATED      VARCHAR2(1),
  SECONDARY      VARCHAR2(1),
  NAMESPACE      NUMBER,
  EDITION_NAME   VARCHAR2(30)
)partition by list(owner)(
  partition  p1 values('SYS'),
  partition  p2 values('PUBLIC'),
  partition  p3 values('SYSMAN'),
  partition  p4 values('APEX_030200'),
  partition  p5 values('ORDSYS'),
  partition  p6 values('MDSYS'),
  partition  p7 values('XDB'),
  partition  p8 values('OLAPSYS'),
  partition  p9 values('SYSTEM'),
  partition  p_default values(DEFAULT) 
);
insert into TEST_P select * from dba_objects;

commit;

2.局部前缀索引(local nonprefixed index)

create index ind_local_prfixed on TEST_P(owner,object_id) local nologging;
exec dbms_stats.gather_table_stats(user,'TEST_P',cascade => true);
SQL> set autotrace traceonly
SQL> select * from TEST_P where object_id = 4903;
执行计划
----------------------------------------------------------
Plan hash value: 3793878917
------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                          | Name              | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                   |                   |     1 |    97 |    28   (0)| 00:00:01 |       |       |
|   1 |  PARTITION LIST ALL                |                   |     1 |    97 |    28   (0)| 00:00:01 |     1 |    10 |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST_P            |     1 |    97 |    28   (0)| 00:00:01 |     1 |    10 |
|*  3 |    INDEX SKIP SCAN                 | IND_LOCAL_PRFIXED |     1 |       |    27   (0)| 00:00:01 |     1 |    10 |
------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("OBJECT_ID"=4903)
       filter("OBJECT_ID"=4903)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
         38  consistent gets
          0  physical reads
          0  redo size
       1294  bytes sent via SQL*Net to client
        472  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed


SQL> select * from TEST_P where object_id = 4903 and owner='SYS';
执行计划
----------------------------------------------------------
Plan hash value: 1414917495
------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                          | Name              | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                   |                   |     1 |    96 |     2   (0)| 00:00:01 |       |       |
|   1 |  PARTITION LIST SINGLE             |                   |     1 |    96 |     2   (0)| 00:00:01 |   KEY |   KEY |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST_P            |     1 |    96 |     2   (0)| 00:00:01 |     1 |     1 |
|*  3 |    INDEX RANGE SCAN                | IND_LOCAL_PRFIXED |     1 |       |     1   (0)| 00:00:01 |     1 |     1 |
------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("OWNER"='SYS' AND "OBJECT_ID"=4903)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
       1294  bytes sent via SQL*Net to client
        472  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> drop index ind_local_prfixed;

3.局部非前缀索引(local nonprefixed index)

SQL> create index ind_local_nonprfixed on TEST_P(object_id) local nologging;
SQL> select * from TEST_P where object_id = 4903;
执行计划
----------------------------------------------------------
Plan hash value: 449164761
---------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                          | Name                 | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
---------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                   |                      |     1 |    97 |    12   (0)| 00:00:01 |       |       |
|   1 |  PARTITION LIST ALL                |                      |     1 |    97 |    12   (0)| 00:00:01 |     1 |    10 |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST_P               |     1 |    97 |    12   (0)| 00:00:01 |     1 |    10 |
|*  3 |    INDEX RANGE SCAN                | IND_LOCAL_NONPRFIXED |     1 |       |    11   (0)| 00:00:01 |     1 |    10 |
---------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("OBJECT_ID"=4903)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
         22  consistent gets
         44  physical reads
          0  redo size
       1294  bytes sent via SQL*Net to client
        472  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> select * from TEST_P where object_id = 4903 and owner='SYS';
执行计划
----------------------------------------------------------
Plan hash value: 747180801
---------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                          | Name                 | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
---------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                   |                      |     1 |    96 |     2   (0)| 00:00:01 |       |       |
|   1 |  PARTITION LIST SINGLE             |                      |     1 |    96 |     2   (0)| 00:00:01 |   KEY |   KEY |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST_P               |     1 |    96 |     2   (0)| 00:00:01 |     1 |     1 |
|*  3 |    INDEX RANGE SCAN                | IND_LOCAL_NONPRFIXED |     1 |       |     1   (0)| 00:00:01 |     1 |     1 |
---------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("OBJECT_ID"=4903)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
       1294  bytes sent via SQL*Net to client
        472  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)

          1  rows processed

    结论：从实验来看，不管是使用哪种索引，SQL条件中都要使用分区条件，要不然两种索引都要全分区扫描。加了分区条件后，两种索引都可以消除分区，所以我建议还是用局部非前缀索引。