ORA-00059: maximum number of DB_FILES exceeded

If you have this error in your alertSID.log:

ERROR at line 1:
ORA-00059: maximum number of DB_FILES exceeded

You have to increase the number of file allowed for the database. The instance has to be restarted:

SQL> SHOW parameter db_files
--> 1500

SQL> ALTER system SET db_files = 3000 scope = BOTH;
SQL> shutdown immediate
SQL> startup
SQL> SHOW parameter db_files
--> 3000