测试环境ORACLE 11.2.0.
如果连接池设置单个连接闲置时间大于数据库连接超时时间，则连接池中的连接发出数据请求时会出现Connect timeout occurred错误，
这是由于连接超时所产生的问题，在10.2.0.1.0版本中sqlnet.inbound_connect_timeout参数默认为60秒:
下面附加一些数据库问题，转载自网络(http://www.itpub.net/thread-1620597-1-1.html)：
/*
*时间：2009-03-010
*环境：AIX5.3 Oracle10g
*WARNING: inbound connection timed out (ORA-3136)连接超时问题
*/
1、alter_SID.log日志：aaa
Mon Mar 9 02:18:40 2009
ksvcreate: Process(q002) creation failed
Mon Mar 9 02:32:29 2009
WARNING: inbound connection timed out (ORA-3136)
Mon Mar 9 02:33:02 2009
WARNING: inbound connection timed out (ORA-3136)
Mon Mar 9 02:33:19 2009
WARNING: inbound connection timed out (ORA-3136)
2、sqlnet.log日志
Fatal NI connect error 12170.
VERSION INFORMATION:
TNS for IBM/AIX RISC System/6000: Version 10.2.0.1.0 - Production
TCP/IP NT Protocol Adapter for IBM/AIX RISC System/6000: Version 10.2.0.1.0 - Production
Oracle Bequeath NT Protocol Adapter for IBM/AIX RISC System/6000: Version 10.2.0.1.0 - Production
Time: 09-MAR-2009 02:32:29
Tracing not turned on.
Tns error struct:
ns main err code: 12535
TNS-12535: TNS
peration timed out
ns secondary err code: 12606
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0
Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=10.171.4.201)(PORT=3663))
3、参考官方说明关于该警告的说明：
Note:465043.1
The "WARNING: inbound connection timed out (ORA-3136)" in the alert log indicates that the client was not able to complete it's authentication within the period of time specified by parameter SQLNET.INBOUND_CONNECT_TIMEOUT.
You may also witness ORA-12170 without timeout error on the database server sqlnet.log file.
This entry would also have the clinet address which failed to get authenticated. Some applications or JDBC thin driver applications may not have these details.
可能的原因：
1.网络攻击，例如半开连接攻击
Server gets a connection request from a malicious client which is not supposed to connect to the database ,
in which case the error thrown is the correct behavior. You can get the client address for which the error was thrown via sqlnet log file.
2.Client在default 60秒内没有完成认证
The server receives a valid client connection request but the client takes a long time to authenticate more than the default 60 seconds.
3.DB负载太高
The DB server is heavily loaded due to which it cannot finish the client logon within the timeout specified.
WARNING: inbound connection timed out (ORA-3136)
这个错误跟 oracle 监听的一个参数有关：SQLNET.INBOUND_CONNECT_TIMEOUT
这个参数从9i开始引入，指定了客户端连接服务器并且提供认证信息的超时时间，如果超过这个时间客户端没有提供正确的认证信息，服务器会自动中止该连接请求，同时会记录试图连接的IP地址和ORA-12170: TNS:Connect timeout occurred错误。
这个参数的引入，主要是防止DoS攻击，恶意攻击者可以通过不停的开启大量连接请求，占用服务器的连接资源，使得服务器无法提供有效服务。在10.2.0.1起，该参数默认设置为60秒
但是，这个参数的引入也导致了一些相关的bug。比如：
Bug 5594769 - REMOTE SESSION DROPPED WHEN LOCAL SESSION SHARED AND INBOUND_CONNECT_TIMEOUT SET
Bug 5249163 - CONNECTS REFUSED BY TNSLSNR EVERY 49 DAYS FOR INBOUND_CONNECT_TIMEOUT SECONDS
该参数可以通过设置为0来禁用，在服务媏
设置sqlnet.ora文件：SQLNET.INBOUND_CONNECT_TIMEOUT＝0
设置listener.ora文件: INBOUND_CONNECT_TIMEOUT_listenername＝0
然后reload或者重启监听
这是由于连接超时所产生的问题，在10.2.0.1.0版本中sqlnet.inbound_connect_timeout参数默认为60秒，即如果连接时间超过60秒则提示超时，而在其他10G版本中这两个参数默认为0，即无限制。
如何操作：
一、查看数据库中listener.ora中的inbound_connect_timeout参数值
1、进入lsnrctl，
LHXXDBS01raoms> lsnrctl
2、查看inbound_connect_timeout参数：
LSNRCTL> show inbound_connect_time
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=LHXXDBS)(PORT=1568)))
LISTENER parameter "inbound_connect_timeout" set to 0
The command completed successfully
如果inbound_connect_timeout参数值不为0，则可以修改为0
修改：
LSNRCTL> set inbound_connect_time 0
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=LHXXDBS)(PORT=1568)))
LISTENER parameter "inbound_connect_timeout" set to 0
The command completed successfully
二、修改/oracle/oms/102_64/network/admin/sqlnet.ora
Vi sqlnet.ora
SQLNET.INBOUND_CONNECT_TIMEOUT = 0
保持退出 wq!
三、重新载入listener
LSNRCTL> reload
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=LHXXDBS)(PORT=1568)))
The command completed successfully
第二天观察没有出现WARNING: inbound connection timed out (ORA-3136)连接超时的现象了。
调度时程的忙百分比（当这个比例超过50时，需要增加DISPATCHERS 的值）：
Select Name "Dispatcher",
Network,
(Round(Sum(Busy) / (Sum(Busy) + Sum(Idle)), 4)) * 100 "Busy_Rate"
From V$dispatcher
Group By Name, Network;