ORACLE 表移动后必须做的事

概述

移动一张表实际上是一个重组过程，数据库会将原来的数据复制到新的地方。但是如果你发现这个表在移动后性能下降了，可能是你的索引没有重建。本文将指导您找到依赖索引并重建它们。

将表从示例移动到用户

SQL> select tablespace_name from dba_tables where owner = 'HR' and table_name = 'EMPLOYEES';

TABLESPACE_NAME
------------------------------
EXAMPLE

SQL> alter table hr.employees move tablespace users;

Table altered.

SQL> select tablespace_name from dba_tables where owner = 'HR' and table_name = 'EMPLOYEES';

TABLESPACE_NAME
------------------------------
USERS

查看哪些索引取决于此表

SQL> column index_name format a30;
SQL> column tablespace_name format a30;
SQL> column status format a10;
SQL> select index_name, tablespace_name, status from dba_indexes where owner = 'HR' and table_name = 'EMPLOYEES';

INDEX_NAME                     TABLESPACE_NAME                STATUS
------------------------------ ------------------------------ ----------
EMP_JOB_IX                     EXAMPLE                        UNUSABLE
EMP_DEPARTMENT_IX              EXAMPLE                        UNUSABLE
EMP_MANAGER_IX                 EXAMPLE                        UNUSABLE
EMP_NAME_IX                    EXAMPLE                        UNUSABLE
EMP_EMAIL_UK                   EXAMPLE                        UNUSABLE
EMP_EMP_ID_PK                  EXAMPLE                        UNUSABLE

6 rows selected.

如您所见，所有依赖索引都是UNUSABLE。这意味着，数据库不会自动重建它们。你必须自己做。

编写所有重建语句，然后执行它们

SQL> select 'alter index ' || owner || '.' ||index_name || ' rebuild tablespace users;' as SQL_TO_BE_EXECUTED from dba_indexes where owner = 'HR' and table_name = 'EMPLOYEES';

SQL_TO_BE_EXECUTED
--------------------------------------------------------------------------------
alter index EMP_JOB_IX rebuild tablespace users;
alter index EMP_DEPARTMENT_IX rebuild tablespace users;
alter index EMP_MANAGER_IX rebuild tablespace users;
alter index EMP_NAME_IX rebuild tablespace users;
alter index EMP_EMAIL_UK rebuild tablespace users;
alter index EMP_EMP_ID_PK rebuild tablespace users;

6 rows selected.

或者您可以重建原始表空间的索引。

SQL> select 'alter index ' || owner || '.' ||index_name || ' rebuild tablespace ' || tablespace_name || ';' as SQL_TO_BE_EXECUTED from dba_indexes where owner = 'HR' and table_name = 'EMPLOYEES';

SQL_TO_BE_EXECUTED
--------------------------------------------------------------------------------
alter index HR.EMP_DEPARTMENT_IX rebuild tablespace EXAMPLE;
alter index HR.EMP_NAME_IX rebuild tablespace EXAMPLE;
alter index HR.EMP_MANAGER_IX rebuild tablespace EXAMPLE;
alter index HR.EMP_EMP_ID_PK rebuild tablespace EXAMPLE;
alter index HR.EMP_EMAIL_UK rebuild tablespace EXAMPLE;
alter index HR.EMP_JOB_IX rebuild tablespace EXAMPLE;

6 rows selected.

请注意，我们在新表空间USERS中重建索引。也就是说，对于索引，REBUILD相当于表中的MOVE

重建后检查状态

SQL> select index_name, tablespace_name, status from dba_indexes where owner = 'HR' and table_name = 'EMPLOYEES';

INDEX_NAME                     TABLESPACE_NAME                STATUS
------------------------------ ------------------------------ ----------
EMP_JOB_IX                     USERS                          VALID
EMP_DEPARTMENT_IX              USERS                          VALID
EMP_MANAGER_IX                 USERS                          VALID
EMP_NAME_IX                    USERS                          VALID
EMP_EMAIL_UK                   USERS                          VALID
EMP_EMP_ID_PK                  USERS                          VALID

6 rows selected.

所有索引都变为VALID，表明所重建的索引有效。