checkpoint是一个数据库事件，它将已修改的数据从高速缓存刷新到磁盘，并更新控制文件和数据文件。

alter database archivelog;

alter databse open;

SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     4
Next log sequence to archive   6
Current log sequence           6
SQL> alter system archive log current;

SQL> alter system archive log current;

System altered.

SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     5
Next log sequence to archive   7
Current log sequence           7

SQL> alter system checkpoint;

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     5
Next log sequence to archive   7
Current log sequence           7

SQL> ALTER SYSTEM SWITCH LOGFILE;

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     6
Next log sequence to archive   8
Current log sequence           8