一、创建索引注意事项

1、预估索引大小

2、查看索引表空间可用空间大小

3、查看临时表空间大小

4、业务空闲期创建

5、可以考虑在线、并行、nologging模式

二、预估索引方法

操作步骤如下：

SQL> explain plan for create index idx_object_id on tt(object_id) ;

Explained.

SQL> set lines 200 pages 1000

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

PLAN_TABLE_OUTPUT

-------------------------------------------------------------------------------------------------------------------------------

Plan hash value: 3757763116

----------------------------------------------------------------------------------------

| Id  | Operation              | Name          | Rows  | Bytes | Cost (%CPU)| Time     |

----------------------------------------------------------------------------------------

|   0 | CREATE INDEX STATEMENT |               |  2762K|    13M| 22958   (1)| 00:04:36 |

|   1 |  INDEX BUILD NON UNIQUE| IDX_OBJECT_ID |       |       |            |          |

|   2 |   SORT CREATE INDEX    |               |  2762K|    13M|            |          |

|   3 |    TABLE ACCESS FULL   | TT            |  2762K|    13M| 21560   (1)| 00:04:19 |

----------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Note

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   - estimated index size: 67M bytes

14 rows selected.

Elapsed: 00:00:00.01

SQL>