ORA-03135: connection lost contact in the alert log of a Primary DB

Problem:

The following error was keep coming in the alertlog of a 19c Primary DB having a standby DB:

ORA-03135: connection lost contact

 

Analysis:

The logfile contains the following error, which refers to a problem at the standby archive log dest side:

After trying to troubleshoot for long time and after sending tons of logs to Oracle Support, I figured  there was an archive destination on another standby DB was mistakenly left enabled after a DR drill to send the archivelogs to the same standby DB which was causing this issue!

Solution:

Disable all archivelog destination that send the arhicvelog to the standby DB causing the issue, and enable it only from one database (which is the primary in my case).

On the additional DR which was sending archivelogs to the same standby and causing that error:

SQL> alter system set log_archive_dest_state_4=defer;

Make sure to enable the archive destination from only one DB which is the Primary in my case:

SQL> alter system set log_archive_dest_state_4=enable;