分类：
2008-10-28 17:46:32
SQL> explain plan for
2 alter index test.IND_OBJECT_ID rebuild;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost |
-------------------------------------------------------------------------
| 0 | ALTER INDEX STATEMENT | | 6235 | 18705 | 10 |
| 1 | INDEX BUILD NON UNIQUE| IND_OBJECT_ID | | | |
| 2 | SORT CREATE INDEX | | 6235 | 18705 | |
| 3 | INDEX FAST FULL SCAN| IND_OBJECT_ID | 6235 | 18705 | |
-------------------------------------------------------------------------
Note: cpu costing is off
11 rows selected.
SQL> explain plan for
2 alter index test.IND_OBJECT_ID rebuild online;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost |
-------------------------------------------------------------------------
| 0 | ALTER INDEX STATEMENT | | 6235 | 18705 | 10 |
| 1 | INDEX BUILD NON UNIQUE| IND_OBJECT_ID | | | |
| 2 | SORT CREATE INDEX | | 6235 | 18705 | |
| 3 | TABLE ACCESS FULL | T | 6235 | 18705 | 10 |
-------------------------------------------------------------------------
Note: cpu costing is off
11 rows selected.
SQL>
可见rebuild 和rebuild online的扫描方式不同，但都会发生sort.
在rebuild online 时会报错
ORA-08120: Need to create SYS.IND_ONLINE$ table in order to (re)build index
Cause: Alter index Build/Rebuild online require existing of SYS.IND_ONLINE$ table.
Action: User/DBA needs to create sys.ind_online$ before alter the index /rdbms/admin/catcio.sql contains script to create ind_online$.
解决方法就是运行catcio.sql 创建SYS.IND_ONLINE$表
SQL> conn / as sysdba
Connected.
SQL> @D:oracleora92rdbmsadmincatcio
除了扫描方式不同外，rebuild 会阻塞dml语句而rebuild online则不会。
rebuild online时系统会产生一个SYS_JOURNAL_xxx的IOT类型的系统临时日志表，所有rebuild online时索引的变化都记录在这个表中，当新的索引创建完成后，把这个表的记录维护到新的索引中去，然后drop掉旧的索引，rebuild online就完成了。
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