ORA-02020: too many database links in use

ERROR:

ORA-02020: too many database links in use

CAUSE: 

 The current session has exceeded the INIT.ORA open_links maximum.\

SOLUTION:

SQL> show parameter open_links;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------
open_links                           integer     4
open_links_per_instance              integer     4

Action:
Increase the open_links limit, or free up some open links by committing or rolling back the transaction and canceling open cursors that reference remote databases.

SQL> alter system set open_links_per_instance=10 scope=spfile;
SQL> alter system set open_links=10 scope=spfile;

and then, bounce the database.