ORA-03135: connection lost contact

This error may be accompanied by ORA-03113: end-of-file on communication channel. This actually means that your session has been dropped and there could be different reasons which might have caused this. Most commonly; a firewall between client and server could have caused this session/connection drop, if firewall senses some session to
be idle for a longer period of time. This session drop timeout setting is done in the firewall and to deny its effect, SQLNET profile parameter “expire_time” could be used to keep the database sessions alive to avoid any connection drop by the firewall.

SQLNET.EXPIRE_TIME

To avoid the problem of "unwanted" disconnection, sqlnet.expire_time can be added in the sqlnet.ora file of database server. This parameter has a value in minutes and it would cause database server to send a packed to each client connect to it at an interval equal to the value of this parameter. This small packet sending would actually deceive firewall so that it considers it an active connection and does not drop it.

We can initially set it to a value of 10 minutes which can be alerted with coordination of network admin who can help to find out firewall settings. Add the following line in $ORACLE_HOME/network/admin/sqlnet.ora

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SQLNET.EXPIRE_TIME = 10

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Actual work of this parameter is to check the client sessions which might have exited but server process related to the session is still intact; so that this server process could also be terminated and resources could be released. For details about this parameter, please Click Here