把数据库打开到mount状态，生产库记住要先shutdown immediate，
然后再startup mount，shutdown abort容易带来灾难性问题
sys@HYJT> startup force mount
ORACLE instance started.
Total System Global Area 184549376 bytes
Fixed Size 1218412 bytes
Variable Size 67111060 bytes
Database Buffers 113246208 bytes
Redo Buffers 2973696 bytes
Database mounted.
在mount状态下修改数据库归档模式
sys@HYJT> alter database noarchivelog;
Database altered.
查看修改结果
sys@HYJT> select log_mode from v$database;
LOG_MODE
------------
NOARCHIVELOG
打开数据库到open
sys@HYJT> alter database open;
Database altered.
查看归档状态
sys@HYJT> archive log list;
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 1
Current log sequence 3