When you give this command 'alter database switch logfile' then he generate a checkpoint number which shows that your courrent redo log is full and he write the second redo log. If you want to information about checkpoint the you have to use this view 'V$datafile'.
log switch occurs when current redo logfile gets full and lgwr writes redo to next redo logfile. Even we can perform log switch with the command also before we execute the sql execute following statement SQL> select status from v$log;
STATUS ---------------- UNUSED UNUSED CURRENT------>active redo logfile 3
After execute the statement
SQL> alter system switch logfile;
System altered.
SQL> select status from v$log;
STATUS ---------------- CURRENT---->now it have changed the position from logfile3 to logfile1 UNUSED ACTIVE
