错误现象：
ORA-02020: too many database links in use
Cause: The current session has exceeded the INIT.ORA open_links maximum.
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.
再查看参数：
SQL> show parameter open_links;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
open_links integer 10
open_links_per_instance integer 4
Oracle默认是4:
SQL> alter system set open_links=10 scope=spfile;
重启下数据库就好了!