Oracle在线重定义

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<10001;

10000 rows created.

SQL> 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<1001;

1000 rows created.

SQL> 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 <=24;

24 rows created.

SQL> 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 <=10;

ID FID C
---------- ---------- ----------
1 1 0
2 2 0
3 3 0
4 4 0
5 5 0
6 6 0
7 7 0
8 8 0
9 9 0
10 10 0

10 rows selected.

--删除过渡表了，收工。这时也可以考虑修改索引，约束触发器的名称与原来保持一致

SQL> drop table inter_test cascade constraints purge;

Table dropped.

本文转自MIKE老毕 51CTO博客，原文链接：http://blog.51cto.com/boylook/1298615，如需转载请自行联系原作者