Oracle Error Message
ORA-16857: standby disconnected from redo source for longer than specified threshold
Reason for the Error
The amount of time the standby was disconnected from the redo source database exceeded the value specified by the ‘TransportDisconnectedThreshold’ database property. It is caused by no network connectivity between the redo source and the standby databases.
Solution
Ensure that there is network connectivity between the redo source and standby databases, and the redo source is working properly.