alter index rebuild和alter index rebuild online的区别

SQL> explain plan for alter index t_index3 rebuild;

已解释。

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

PLAN_TABLE_OUTPUT

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

Plan hash value: 2701019691

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

----

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

|

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

----

PLAN_TABLE_OUTPUT

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

| 0 | ALTER INDEX STATEMENT | | 1000 | 2000 | 1 (0)| 00:00:

01 |

| 1 | INDEX BUILD NON UNIQUE | T_INDEX3 | | | |

|

| 2 | BITMAP COMPACTION | | | | |

|

| 3 | SORT CREATE INDEX | | 1000 | 2000 | |

|

PLAN_TABLE_OUTPUT

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

| 4 | INDEX FAST FULL SCAN| T_INDEX3 | 1000 | 2000 | 1 (0)| 00:00:

01 |

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

----

已选择11行。

可以看到是对索引进行扫描。

SQL> explain plan for alter index t_index3 rebuild online;

已解释。

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

PLAN_TABLE_OUTPUT

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

Plan hash value: 3732900664

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

----

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

|

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

----

PLAN_TABLE_OUTPUT

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

| 0 | ALTER INDEX STATEMENT | | 1000 | 2000 | 1 (0)| 00:00:

01 |

| 1 | INDEX BUILD NON UNIQUE | T_INDEX3 | | | |

|

| 2 | BITMAP COMPACTION | | | | |

|

| 3 | SORT CREATE INDEX | | 1000 | 2000 | |

|

PLAN_TABLE_OUTPUT

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

| 4 | BITMAP CONSTRUCTION | | | | |

|

| 5 | TABLE ACCESS FULL | T | 1000 | 2000 | 1 (0)| 00:00:

01 |

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

----

已选择12行。

可以看到是对表进行扫描。

结论：

主要区别：是否阻塞DML操作和扫描数据的不同

在OLTP系统中，rebuild online比较合适。