在线重定义[@more@]Oracle9i之前，表数据的整理是通过 alter table XXX move [tablespace XX]进行的。如果表非常大，IO又不快的时候，move的过程可能相当漫长，不能算是HA特性。因此在HA的在线维护中，基本不会利用move来重组大型表，而且move后的表需要重建索引。而在9i引入的dbms_redefinition。该过程的内部原理其实就是采用了MV的机制，类似在原表建立一个prebuilt的MV然后一直增量刷新到数据差别最小。Oracle在很小的停顿中，完成最后一点的增量同步，达到完全同步后，把原表与新表换个名字，由于换名操作仅仅是数据字典，所以最终切换时间非常短。
--首先建立一个用来测试外键约束的表test_refed
SQL> create table test_refed(id number primary key);
Table created.
SQL> insert into test_refed select rownum from dba_objects where rownum commit;
Commit complete.
--创建我们准备修改表定义的表test，未分区
SQL> create table test(id number,fid number);
Table created.
SQL> insert into test select rownum,rownum from dba_objects where rownum commit;
Commit complete.
--添加主键约束以及外键约束，并在外键上建立索引
SQL> alter table test add constraint pk_test primary key(id);
Table altered.
SQL> alter table test add constraint fk_test_refed_id foreign key(fid) references test_refed(id);
Table altered.
SQL> create index idx_test_fid on test(fid);
Index created.
--创建基于test表的触发器
SQL> create trigger tr_test
2 before insert on test for each row
3 begin
4 null;
5 end;
6 /
Trigger created.
--准备工作：调用dbms_redefinition.can_redef_table来验证boylook.test是否可以在线重定义。一般情况没有主键等会报错。
SQL> begin
2 dbms_redefinition.can_redef_table('BOYLOOK','TEST');
3 end;
4 /
PL/SQL procedure successfully completed.
--创建需要重新定义的过渡表inter_test，这是一个分区表，以后将把原表所有数据在线转移到该表当中。注意到，该表比原表test还多一个字段c
SQL> create table inter_test(id number,fid number,c number)
2 partition by range(id)
3 (partition p1 values less than(400),
4 partition p2 values less than(800),
5 partition p3 values less than(maxvalue));
Table created.
SQL> alter table inter_test add constraint pk_inter_test primary key(id);
Table altered.
--执行在线重定义
注：调用这个存储过程需要create/alter/drop/lock/select any table权限
SQL> exec dbms_redefinition.start_redef_table('BOYLOOK','TEST','INTER_TEST','id id,fid fid,0 c');
PL/SQL procedure successfully completed.
--验证数据是否刷了过去
SQL> select count(*) from inter_test;
COUNT(*)
----------
1000
--继续对原表test进行操作
SQL> insert into test select rownum+1000,rownum+1000 from dba_objects where rownum commit;
Commit complete.
SQL> select count(*) from test;
COUNT(*)
----------
1024
SQL> select count(*) from inter_test;
COUNT(*)
----------
1000
--执行表同步
注：这一步不是必须的，但是对于比较大的表，中间运行增量同步有助于减少切换时间。
SQL> exec dbms_redefinition.sync_interim_table('BOYLOOK','TEST','INTER_TEST');
PL/SQL procedure successfully completed.
--我们发现数据同步的过来
SQL> select count(*) from inter_test;
COUNT(*)
----------
1024
--将原表test的约束，索引，触发器迁移过来
注：这里最好要检查一下授权。检查test以前的权限，并给中间表inter_test赋予同样的权限。否则原表的权限不会转移到新表
SQL> alter table inter_test add constraint fk_inter_refed_id foreign key(fid) references test_refed(id);
Table altered.
SQL> create index idx_inter_test_fid on inter_test(fid);
Index created.
SQL> create or replace trigger tr_inter_test
2 before insert on inter_test for each row
3 begin
4 null;
5 end;
6 /
Trigger created.
--执行重定义完成的过程。Oracle完成了表test到表inter_test的换名工作，只是所有的约束，索引或触发器名称还是保持着原来表上面的名称
SQL> exec dbms_redefinition.finish_redef_table('BOYLOOK','TEST','INTER_TEST');
PL/SQL procedure successfully completed.
SQL> desc test;
Name Null? Type
----------------------------------------- -------- ----------------------------
ID NOT NULL NUMBER
FID NUMBER
C NUMBER
SQL> desc inter_test;
Name Null? Type
----------------------------------------- -------- ----------------------------
ID NOT NULL NUMBER
FID NUMBER
SQL> select table_name,partition_name from user_tab_partitions where table_name ='TEST';
TABLE_NAME PARTITION_NAME
------------------------------ ------------------------------
TEST P1
TEST P2
TEST P3
SQL> select table_name,constraint_name,status from user_constraints where table_name in('TEST','INTER_TEST');
TABLE_NAME CONSTRAINT_NAME STATUS
------------------------------ ------------------------------ --------
INTER_TEST PK_TEST ENABLED
INTER_TEST FK_TEST_REFED_ID DISABLED
TEST PK_INTER_TEST ENABLED
TEST FK_INTER_REFED_ID ENABLED
SQL> select table_name,index_name from user_indexes where table_name in('TEST','INTER_TEST');
TABLE_NAME INDEX_NAME
------------------------------ ------------------------------
TEST PK_INTER_TEST
TEST IDX_INTER_TEST_FID
INTER_TEST PK_TEST
INTER_TEST IDX_TEST_FID
SQL> select table_name,trigger_name from user_triggers where table_name in('TEST','INTER_TEST');
TABLE_NAME TRIGGER_NAME
------------------------------ ------------------------------
TEST TR_INTER_TEST
INTER_TEST TR_TEST
SQL> select * from test where rownum drop table inter_test cascade constraints purge;
Table dropped.
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