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  Svetoslav Gyurov

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Svetoslav Gyurov

In my earlier post I discussed what Dead Connection Detection is and why you should use it – read more here Oracle TNS-12535 and Dead Connection Detection

The pre-12c implementation of DCD used TNS packages to “ping” the client and relied on the underlying TCP stack which sometimes may take longer. Now in 12c this has changed and DCD probes are implemented by TCP Stack. The DCD probes will now use the TCP KEEPALIVE socket option to check if the connection is still usable.

To use the new implementation set the SQLNET.EXPIRE_TIME in sqlnet.ora to the amount of time between the probes in minutes. If the operating system supports TCP keep-alive tuning then Oracle Net automatically uses the new method. The new mechanism is supported on all platforms except on Solaris.

The following parameters are associated with the TCP keep-alive probes:
TCP_KEEPIDLE – specifies the timeout of no activity until the probe is sent. The parameter takes value from SQLNET.EXPIRE_TIME.
TCP_KEEPCNT – number of keep-alive probes to be sent, it is always set to 10.
TCP_KEEPINTVL – specifies the delay between probes if a keep-alive packets are sent and no acknowledgment is received, it is always set to 6.

If you need to revert to the pre-12c DCD mechanism (10 bytes TNS data) add the following parameters in sqlnet.ora:
USE_NS_PROBES_FOR_DCD=true