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14; OWNER OBJECT_NAME SUBOBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE CREATED LAST_DDL_TIME TIMESTAMP STATUS T G S NAMESPACE EDITION_NAME ------------------------------ -------------------------------------------------------------------------------------------------------------------------------- ------------------------------ ---------- -------------- ------------------- -------------- -------------- ------------------- ------- - - - ---------- ------------------------------ HR T 76714 76714 TABLE 22-4月 -15 22-4月 -15 2015-04-22:12:39:06 VALID N N N 1

我们在重建索引时，为了不影响系统性能，往往：
alter index index_name rebuild online;
但是我们为什么不：alter index index_name rebuild
下面简单操作示范：
SQL> create table ttt as select * from dba_objects;
表已创建。

SQL> select count(*) from dba_objects;


COUNT(*)
----------
72746
SQL> create index index_id on TTT(OBJECT_ID);

索引已创建。

SQL> set autotrace traceonly;
SQL> SELECT * FROM TTT;

已选择72746行。

执行计划

----------------------------------------------------------
Plan hash value: 774701505


--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51569 | 10M| 283 (1)| 00:00:04 |
| 1 | TABLE ACCESS FULL| TTT | 51569 | 10M| 283 (1)| 00:00:04 |
--------------------------------------------------------------------------


Note
-----
- dynamic sampling used for this statement (level=2)

统计信息

----------------------------------------------------------
308 recursive calls
0 db block gets
5909 consistent gets
1035 physical reads
0 redo size
8067725 bytes sent via SQL*Net to client
53755 bytes received via SQL*Net from client
4851 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
72746 rows processed

SQL> alter index index_id rebuild;

索引已更改。
SQL> SELECT * FROM TTT;

已选择72746行。

执行计划

----------------------------------------------------------
Plan hash value: 774701505


--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 51569 | 10M| 283 (1)| 00:00:04 |
| 1 | TABLE ACCESS FULL| TTT | 51569 | 10M| 283 (1)| 00:00:04 |
--------------------------------------------------------------------------


Note
-----
- dynamic sampling used for this statement (level=2)

统计信息

----------------------------------------------------------
36 recursive calls
0 db block gets
5886 consistent gets
0 physical reads
0 redo size
8067725 bytes sent via SQL*Net to client
53755 bytes received via SQL*Net from client
4851 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
72746 rows processed

SQL> alter index index_id rebuild online;

索引已更改。

SQL> SELECT * FROM TTT;

已选择72746行。

执行计划

----------------------------------------------------------
Plan hash value: 774701505


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

lock(二)