Unresponsive DB Link
A dead DB link means an unresponsive remote connection between databases. In fact, the db link may have finished his job without any return.
In some cases, the executed stored procedure seems hanging, actually, it's still waiting for some message from the remote DB link, but with no luck.
Sometimes, the symptom would be more obvious if databases are in a complicated or restrictive network environment that you are unable to do any change.
Therefore, we should make the network communication more constantly and more often. To make the communication more active and penetrating, we increase the frequency of response.
On both nodes at database level, not at grid level, we set SQLNET.EXPIRE_TIME to specify a time interval, in minutes, to send back a check to verify that connections are still active.
[oracle@primary01 ~]$ vi $ORACLE_HOME/network/admin/sqlnet.ora
[oracle@primary02 ~]$ vi $ORACLE_HOME/network/admin/sqlnet.ora
Any value of SQLNET.EXPIRE_TIME larger than 0, the default value, ensures connections are not left open indefinitely.