錯誤信息：

Fatal NI connect error 12170.

  VERSION INFORMATION:
        TNS for Linux: Version 11.2.0.1.0 - Production
        Oracle Bequeath NT Protocol Adapter for Linux: Version 11.2.0.1.0 - Production
        TCP/IP NT Protocol Adapter for Linux: Version 11.2.0.1.0 - Production
  Time: 08-1月 -2013 14:00:50
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535

TNS-12535: TNS:作業逾時
    ns secondary err code: 12560
    nt main err code: 505

TNS-00505: 作業逾時
    nt secondary err code: 110
    nt OS err code: 0
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=10.12.195.1)(PORT=1452))
Tue Jan 08 14:06:32 2013

問題分析：

11g R1如果出现如上的错误信息会写入到sqlnet.log,11g R2会写入到alert.log，其实出现此错误是正常的现象

解決方法：

Note the time of the client corresponding client connection(s) in the listener log.  Here you may find a particular client,
set of clients or particular applications that are improperly disconnecting causing the timeout errors to be raised and recorder in the database alert log.
You may choose to revert from the new Automatic Diagnostic Repository (ADR) method to prevent the Oracle Net diagnostic details from being written to the alert log(s)
by setting the following Oracle Net configuration parameters:
To revert to Oracle Net Server tracing/logging, set following parameter in the server's sqlnet.ora :

DIAG_ADR_ENABLED = OFF

Also, to back out the ADR diag for the Listener component, set following parameter in the server's listener.ora:

DIAG_ADR_ENABLED_ = OFF

- Where the would be replaced with the actual name of the configured listener(s) in the listener.ora configuration file.  For example,
if the listener name is 'LISTENER', the parameter would read:

DIAG_ADR_ENABLED_LISTENER = OFF
-Reload or restart the TNS Listener for the parameter change to take effect.