今天在一台服务器的日志文件中，发现如下信息：看似是个错误，可是却不影响数据库的运行，但毕竟报错了，看着不舒服，就研究下

Fatal NI connect error 12170.

 VERSION INFORMATION:
   TNS for Linux: Version 11.1.0.7.0 - Production
   Unix Domain Socket IPC NT Protocol Adaptor for Linux: Version 11.1.0.7.0 - Production
   Oracle Bequeath NT Protocol Adapter for Linux: Version 11.1.0.7.0 - Production
   TCP/IP NT Protocol Adapter for Linux: Version 11.1.0.7.0 - Production
 Time: 08-NOV-2011 13:57:10
 Tracing not turned on.
 Tns error struct:
   ns main err code: 12535

TNS-12535: TNS:operation timed out
   ns secondary err code: 12560
   nt main err code: 505

TNS-00505: Operation timed out
   nt secondary err code: 110
   nt OS err code: 0
 Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=IP)(PORT=51345))
查看mos，有幸发现关于该错误的相关文章
Fatal NI connect error 12170′, ‘TNS-12535: TNS:operation timed out’ Reported in 11g Alert Log [ID 1286376.1]
做了一些摘要，算是给自己做个记录，也给不能访问mos的朋友一个参考
1、适用范围
 Oracle Net Services - Version: 11.1.0.6 to 11.2.0.2 - Release: 11.1 to 11.2
Oracle Server - Enterprise Edition - Version: 11.1.0.6 to 11.2.0.2   [Release: 11.1 to 11.2]
Information in this document applies to any platform.
2、问题原因
 These time out related messages are mostly informational in nature.  The messages indicate the specified client connection (identified by the 'Client address:' details) has experienced a time out.  The 'nt secondary err code' identifies the underlying network transport, such as (TCP/IP) timeout limits after a client has abnormally terminated the database connection.
The 'nt secondary err code' translates to underlying network transport timeouts for the following Operating Systems:
For the Solaris system: nt secondary err code: 145:
#define ETIMEDOUT 145
For the Linux operating system: nt secondary err code: 110
ETIMEDOUT 110 Connection timed out
For the HP-UX system: nt secondary err code: 238:
ETIMEDOUT 238
For Windows based platforms: nt secondary err code: 60 (which translates to Winsock Error: 10060)
Description:  A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
The reason the messages are written to the alert log is related to the use of the new 11g Automatic Diagnostic Repository (ADR) feature being enabled by default
3、解决问题
 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.
说明：这个问题是由于Automatic Diagnostic Repository中的 Oracle Net diagnostic在默认的情况下是开启的，当数据库和客户端的连接超过特定时间，就会把这样的信息写入到alert日志中，所以这不是一个致命的问题，如果偶尔出现，可以忽略有点类此ora-3136的错误