ORA-02020 Solution

Error
ORA-02020 – Too many database links in use 

Solution
Current setting:
SQL> show parameter open_links;
-- default is "4"

Change setting permanently:
add this into init.ora file;
*.open_links=10
*.open_links_per_instance=10

Then restart the instance to perform.

Alternative solution
Kill the hanged database link:
At first, find the database link
SQL> SELECT db_link FROM v$dblink;

Then kill it
SQL> alter session close database link ALPERDB.WORLD;