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。 Trackback: http://tb.blog.csdn.net/TrackBack.ASPx?PostId=1479533
