How to solve “ORA-03135 connection lost contact” error?

Question: Users are connected to the database via TNS and abruptly get disconnected. What is the cause of the ORA-03135 error? How can this be resolved?

    ORA-03135: connection lost contact

Answer: According to oerr the description of the ORA-03135 error is below.

    Cause:
    1) Server unexpectedly terminated or was forced to terminate.
    2) Server timed out the connection.

    Action:
    1) Check if the server session was terminated.
    2) Check if the timeout parameters are set properly in SQLNET.ora.

The most common reason is that the database session was idle for a time period greater than the idle timeout setting on the Firewall. This results in the firewall terminating the session.

Solution: Configure Dead Connection Detection (DCD) in the environment by setting a value for SQLNET.EXPIRE_TIME parameter in the $ORACLE_HOME/network/admin/sqlnet.ora file.

Based on this value, the database server will send a packet back to the client. In cases when the packet is not acknowledged, the client connection is closed.

Below the value is set to 15 minutes in the sqlnet.ora file.

SQLNET.EXPIRE_TIME=15

There are two cases to consider with this setting. One with the value lower that the Firewall setting and one with a higher value.

When the value of the SQLNET.EXPIRE_TIME is lower than the Firewall connection timeout, since a packet will always be sent before the fireawall connection timeout threshold the session will not be killed.

In case the value of the SQLNET.EXPIRE_TIME is higher than the Firewall connection timeout, when the firewall kills the session, the database will immediately close the session cleanly.

Note 787354.1 Troubleshooting ORA-3135 Connection Lost Contact
Note 257650.1 Resolving Problems with Connection Idle Timeout With Firewall

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