Fatal NI connect error 12547, connecting to:

Sometimes you may see following error message in your alert log file. There is a similar Fatal NI error 12537 that appears in the alert log file when session exists during the session creation phase. But error 12547 comes when session terminates abnormally. For example, client application crashes without properly exiting the database, or sessions gets disconnected because of a network disconnection.

Fatal NI connect error 12547, connecting to: (LOCAL=NO)~~VERSION INFORMATION: TNS for 64-bit Windows: Version 11.2.0.3.0 - Production Oracle Bequeath NT Protocol Adapter for 64-bit Windows: Version 11.2.0.3.0 - Production~Windows NT TCP/IP NT Protocol Adapter for 64-bit Windows: Version 11.2.0.3.0 - Production Time: 30-MAY-2017 11:51:02~Tracing not turned on. Tns error struct:~ns main err code: 12547 TNS-12547: TNS:lost contact ns secondary err code: 12560 nt main err code: 0~nt secondary err code: 0 nt OS err code: 0~opiodr aborting process unknown ospid (1104)! as a result of ORA-609

This error appears same on Windows or Linux based platforms. When a session suddenly disconnects without properly logging out, the server side process keeps running and oracle needs to kill this session to release the resources held by this session that is no longer there.

This is just an information logged into the alert log file and no action is needed by the DBA. If this error is quite frequent, you may need to investigate about why sessions are disconnecting abnormally so frequently that is causing this error to be logged in the alert log file. If you do not want this informative message to be logged in the alert log file, it can be disabled by adding following parameter in the sqlnet.ora file.

DIAG_ADR_ENABLED = OFF --Reload the listener after adding above line. lsnrctl reload <listener_name>