在之前的文章中，我们看到了如何处理单表在线重定义过程。本篇我们来看一下如何进行关联表的重定义过程。

4、外键关系表重定义

我们先创建出实验数据表。

SQL> create table t_master as select owner, table_name, tablespace_name, status from dba_tables where 1=0;

Table created

SQL> alter table t_master add constraint pk_t_master primary key (owner, table_name);

Table altered

Executed in 0.125 seconds

SQL> create table t_slave as select owner, table_name, column_name from dba_tab_columns where 1=0;

Table created

SQL> alter table T_SLAVE

2    add constraint pk_t_slave primary key (OWNER, TABLE_NAME, COLUMN_NAME);

Table altered

Executed in 0.422 seconds

T_MASTER和T_SLAVE构成主子表关系，插入数据。

SQL> insert into t_master select owner, table_name, tablespace_name, status from dba_tables;

2841 rows inserted

Executed in 0.157 seconds

SQL> commit;

Commit complete

Executed in 0 seconds

SQL> insert into t_slave select owner, table_name, column_name from dba_tab_cols where (owner, table_name) in (select owner, table_name from dba_tables);

32388 rows inserted

Executed in 2.328 seconds

SQL> commit;

Commit complete

Executed in 0 seconds

SQL> alter table T_SLAVE

2    add constraint fk_t_slave_master foreign key (OWNER, TABLE_NAME)

3    references t_master (OWNER, TABLE_NAME);

Table altered

Executed in 0.266 seconds

创建interim中间表对象，主要目标是将数据表按照owner进行分区，转化为分区表。

SQL> create table t_master_interim

2  (owner varchar2(30),

3   TABLE_NAME      VARCHAR2(30),

4   TABLESPACE_NAME VARCHAR2(30),

5   STATUS          VARCHAR2(8)

6  )

7  partition by list(owner)

8  (

9     partition p1 values ('SYS'),

10     partition p2 values (default)

11  )

12  ;

Table created

Executed in 0.156 seconds

SQL> create table t_slave_interim

2  (owner varchar2(30),

3   table_name varchar2(30),

4   column_name varchar2(30)

5  )

6  partition by list(owner)

7  (

8     partition p1 values ('SYS'),

9     partition p2 values (default)

10  )

11  ;

Table created

Executed in 0.032 seconds

进入正式的重定义流程。这个过程，如果处于安全和顺序关系看，应该是先子表后主表似乎好一点。笔者选择了先主表后子表的方法。

--判断是否可以进行在线重定义过程；

SQL> set serveroutput on;

SQL> exec dbms_redefinition.can_redef_table('SCOTT','T_MASTER',options_flag => dbms_redefinition.cons_use_pk);

PL/SQL procedure successfully completed

Executed in 0.172 seconds

SQL> exec dbms_redefinition.can_redef_table('SCOTT','T_SLAVE',options_flag => dbms_redefinition.cons_use_pk);

PL/SQL procedure successfully completed

Executed in 0.015 seconds

T_MASTER表进行重定义过程。

SQL> exec dbms_redefinition.start_redef_table('SCOTT','T_MASTER','T_MASTER_INTERIM',col_mapping => 'owner owner, table_name table_name, tablespace_name tablespace_name, status status',options_flag => dbms_redefinition.cons_use_pk);

PL/SQL procedure successfully completed

Executed in 1.125 seconds

SQL> exec dbms_redefinition.sync_interim_table('SCOTT','T_MASTER','T_MASTER_INTERIM');

PL/SQL procedure successfully completed

Executed in 0.047 seconds

SQL>

SQL> set serveroutput on;

SQL> declare

2    error_count number:=0;

3  begin

4    dbms_redefinition.copy_table_dependents(uname => 'SCOTT',orig_table => 'T_MASTER',

5                                            int_table => 'T_MASTER_INTERIM',

6                                            copy_indexes => dbms_redefinition.cons_orig_params,

7                                            num_errors => error_count);

8    dbms_output.put_line(to_char(error_count));

9  end;

10  /

0

PL/SQL procedure successfully completed

Executed in 6.766 seconds

SQL> exec dbms_redefinition.finish_redef_table('SCOTT','T_MASTER','T_MASTER_INTERIM');

PL/SQL procedure successfully completed

Executed in 1.75 seconds

进行T_SLAVE表重定义过程。

SQL> exec dbms_redefinition.start_redef_table('SCOTT','T_SLAVE','T_SLAVE_INTERIM',col_mapping => 'owner owner, table_name table_name, column_name column_name',options_flag => dbms_redefinition.cons_use_pk);

PL/SQL procedure successfully completed

Executed in 1.484 seconds

SQL> exec dbms_redefinition.sync_interim_table('SCOTT','T_SLAVE','T_SLAVE_INTERIM');

PL/SQL procedure successfully completed

Executed in 0.047 seconds

SQL>

SQL> set serveroutput on;

SQL> declare

2    error_count number:=0;

3  begin

4    dbms_redefinition.copy_table_dependents(uname => 'SCOTT',orig_table => 'T_SLAVE',

5                                            int_table => 'T_SLAVE_INTERIM',

6                                            copy_indexes => dbms_redefinition.cons_orig_params,

7                                            num_errors => error_count);

8    dbms_output.put_line(to_char(error_count));

9  end;

10  /

0

PL/SQL procedure successfully completed

Executed in 6.718 seconds

SQL> exec dbms_redefinition.finish_redef_table('SCOTT','T_SLAVE','T_SLAVE_INTERIM');

PL/SQL procedure successfully completed

Executed in 1.75 seconds

最后，我们检查处理结果。

--分区处理成功；

SQL> select table_name, partition_name from dba_tab_partitions where table_owner='SCOTT' and table_name in ('T_MASTER','T_SLAVE');

TABLE_NAME                     PARTITION_NAME

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

T_MASTER                       P1

T_MASTER                       P2

T_SLAVE                        P1

T_SLAVE                        P2

Executed in 0.031 seconds

约束中存在一些需要额外处理的地方。

SQL> select constraint_name, constraint_type, R_CONSTRAINT_NAME from dba_constraints where wner='SCOTT' and table_name in ('T_MASTER','T_SLAVE');

CONSTRAINT_NAME                CONSTRAINT_TYPE R_CONSTRAINT_NAME

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

TMP$$_FK_T_SLAVE_MASTER0       R               TMP$$_PK_T_MASTER0

SYS_C0011276                   C

SYS_C0011275                   C

SYS_C0011274                   C

PK_T_SLAVE                     P

FK_T_SLAVE_MASTER              R               PK_T_MASTER

SYS_C0011272                   C

SYS_C0011271                   C

PK_T_MASTER                    P

9 rows selected

Executed in 0.141 seconds

由于是分别进行的重定义动作，中间可能有关联裹挟的情况，所以需要额外进行一些处理。主要目标是将Interim数据表删除掉。

SQL> drop table t_slave_interim;

Table dropped

Executed in 0.438 seconds

SQL> alter table t_slave drop constraint "TMP$$_FK_T_SLAVE_MASTER0";

Table altered

Executed in 0.031 seconds

SQL> drop table t_master_interim purge;

Table dropped

Executed in 0.094 seconds

检查约束情况。

SQL> select constraint_name, constraint_type, R_CONSTRAINT_NAME from dba_constraints where wner='SCOTT' and table_name in ('T_MASTER','T_SLAVE');

CONSTRAINT_NAME                CONSTRAINT_TYPE R_CONSTRAINT_NAME

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

PK_T_MASTER                    P

PK_T_SLAVE                     P

FK_T_SLAVE_MASTER              R               PK_T_MASTER

SYS_C0011271                   C

SYS_C0011272                   C

SYS_C0011274                   C

SYS_C0011275                   C

SYS_C0011276                   C

8 rows selected

Executed in 0.125 seconds

重定义成功。

5、结论和讨论

Oracle在线重定义是一种非常强大的定义工具。这个系列只是介绍了该特性中最常用的一些流程和方法。其他一些诸如register对象和重命名的方法，在一些特定场合下有比较好的使用空间。

应该说，Oracle在线重定义是一种平滑性能、减少锁定、提高系统整体可用性的解决方案。从操作时间和空间消耗上，在线重定义并不具有很高的优势。对于7*24小时的系统，该特性是一种不错的选择。