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GOAL
All abnormally terminated sessions between a database server and a client must be disconnected automatically

SOLUTION

 
Dead Connection Detection (DCD) is intended primarily for environments in which clients power down their systems or client machines crash unexpectedly without disconnecting from Oracle Database sessions.

This feature is configured on an Oracle Database server side and it is controlled/enabled by using parameter SQLNET.EXPIRE_TIME in sqlnet.ora file

Purpose
To specify a time interval, in minutes, to send a check to verify that client/server connections are active.

Usage Notes
Setting a value greater than 0 ensures that connections are not left open indefinitely, due to an abnormal
client termination. If the system supports TCP keepalive tuning, then Oracle Net Services automatically uses
the enhanced detection model, and tunes the TCP keepalive parameters

If the probe finds a terminated connection, or a connection that is no longer in use, then it returns 
an error, causing the server process to exit.This parameter is primarily intended for the database server, 
which typically handles multiple connections at any one time. Limitations on using this terminated 
connection detection feature are:
  • It is not allowed on bequeathed connections.
  • Though very small, a probe packet generates additional traffic that may downgrade network performance.
  • Depending on which operating system is in use, the server may need to perform additional processing to distinguish the connection probing event from other events that occur. This can also result in degraded network performance.
Default 0 Minimum Value 0 Recommended Value 10 Example SQLNET.EXPIRE_TIME=10

 
For instance, to test every 10 minutes that existing connected client sessions are still alive.

[oracle@dbpilot.net ~]$ cat $ORACLE_HOME/network/admin/sqlnet.ora
SQLNET.EXPIRE_TIME=10

 
REFERENCES
Database Net Services Reference 12c

 
 

Version  : 22:22 11.08.2020
Database : 11.2.0.4