A while ago, OEM report some alert messages to us:
Wait class "Network" was consuming significant database time.
Wait event "SQL*Net more data from client" in wait class "Network"
was consuming significant database time. We also see a 30ms slower to render our web pages.
According to Oracle doc,
SQL*Net more data from client
The server is performing another send to the client. The previous operation was also a send to the client.
It is not of much help.
The OEM gives a more clear indication:
Investigate the cause for high “SQL*Net more data from client” waits in Module “JDBC Thin Client”.
It is telling us that something is wrong with the JDBC drivers.
Chris May find a good article here
The cause of this event was a sequence of parse calls that passed excessively long SQL text strings through SQL*Net from the client to the server (instead of using stored procedure calls to accomplish the same thing). The long SQL text strings wouldn’t fit into a single SQL*Net packet, so the Oracle kernel spent a considerable amount of time awaiting second and subsequent SQL*Net packets during parse calls.
Hibernate, the ORM tools used by our application, generates long SQLs. Instead of select * from table, it use select col_1, col_2 from table.
After upgrading to latest JDBC driver, the problem fixed.