As a long-time performance DBA, I’ve often felt that it is important to know something about troubleshooting the layers that are upstream and downstream of the database in the technology stack.  Lately, I’ve been making use of packet captures and Wireshark to solve tough issues in the TCP layer.  We recently resolved a long-standing issue with TCP retransmissions that were causing connection drops between an application server and one of our databases and I thought this might help others faced with similar issues.

This problem started with a series of TNS-12535 messages that were seen in the Oracle alert logs for one of our databases:

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