原因

Doc ID 260819.1

The problem is that these Data Guard protection mode will not allow the database to be opened without a Standby Database available and a corresponding setup log_archive_dest_n. Therefore the Data Guard Protection Mode must be reduced while the database is mounted.

SELECT PROTECTION_MODE, PROTECTION_LEVEL FROM V$DATABASE;

解决

SQL>startup mount;

SQL> alter database set standby to maximize performance;

SQL> alter database open;