今天在做测试的时候想查询数据文件对应的表空间信息，desc dba_Data_files视图时发现报不存在这个对象。当时以为自己的DB在mount下没法查询是正常的，后来在DB OPEN下查询 dba_data_files还是报不存在这个对象。顿时感觉疑惑了，其他对象都查询正常，唯独DBA_*的视图都不能正常查询使用。查询MOS（文档 ID 296235.1） 发现如下描述：
APPLIES TO:
Oracle Database - Enterprise Edition - Version 8.1.7.4 to 11.2.0.1 [Release 8.1.7 to 11.2]
Information in this document applies to any platform.
SYMPTOMS
If you describe any DBA_* Views (Data dictionary views) in a mount stage, than you will not be able to
describe those views even after opening the database.
You can test as follows:
+ Shutdown the database.
SQL> Shutdown immediate
+ Mount the database.
SQL> Startup Mount
+ Describe any Data Dictionary view.
SQL> DESC DBA_DATA_FILES
ERROR:
ORA-04043: object DBA_DATA_FILES does not exist.
+ Open the Database.
SQL> ALTER DATABASE OPEN;
Database altered
+ Describe the same Data Dictionary view.
SQL> DESC DBA_DATA_FILES
ERROR:
ORA-04043: object DBA_DATA_FILES does not exist
*** Error will appear till we bounce the Database / flush the shared pool.
CAUSE
This is related to Bug 2365821
Abstract: ORA-4043 ON DBA_* TABLES IF THEY ARE DESCRIBED IN A MOUNT STAGE.
SOLUTION
Available workarounds are:
1) Don't describe the dba_* views at mount stage.
OR
2) If you issue DESC of any DBA_*views at mount stage, then shutdown and restart the DB instance.
OR
3) Flush the shared pool.
SQL> Alter system flush shared_pool;
and then reissue the failing command.
正是由于我在数据库mount状态下查询dba_data_files视图，导致遭遇oracle 数据库产品的Bug 2365821，数据库即使OPEN下也不能正常使用dba_*视图。
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