数据库：ORA-01502 state unusable错误成因和解决方法(二)

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ORA-01502 state unusable错误成因和解决方法(二)

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SQL> create table t(a number);

Table created.

现在，我们建立一个唯一索引来看看：
SQL> create unique index idx_t on t(a);

Index created.

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='T';

no rows selected

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

INDEX_NAME INDEX_TYPE TABLESPACE_NAME TABLE_TYPE STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T NORMAL DATA_DYNAMIC TABLE VALID

SQL> insert into t values(1);

1 row created.

SQL> commit;

Commit complete.

将索引手工修改为unusable状态（模拟发生索引失效的情况）：
SQL> alter index idx_t unusable;

Index altered.

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

我们看到这是，已经不能正常往表中插入数据：
SQL> insert into t values(2);
insert into t values(2)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of such index is in unusable state

首先，我们通过重建索引（rebuild index）的方法来解决问题：
SQL> alter index idx_t rebuild;

Index altered.

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

SQL> insert into t values(2);

1 row created.

SQL> commit;

Commit complete.

SQL>

现在我们再次模拟索引失效(unusable状态)：
SQL> alter index idx_t unusable;

Index altered.

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

SQL> insert into t values(3);
insert into t values(3)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of such index is in unusable state

然后，看看是否可以通过设置参数skip_unusable_indexes=true来解决问题：
SQL> alter session set skip_unusable_indexes=true;

Session altered.

SQL> insert into t values(3);
insert into t values(3)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of such index is in unusable state

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

SQL> alter index idx_t rebuild;

Index altered.

SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';

SQL> insert into t values(3);

1 row created.

SQL> commit;

Commit complete.

SQL>
很显然，对于unique index，通过简单的设置参数是不能解决问题的，要解决unique index 失效的问题，只能通过重建索引来实现。

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