Oracle数据库监听非常慢，基本hang住故障处理
测试人员邮件反馈：
订购数据库的连接非常慢，甚至是无法连接，想要我检查看看。
经查看：
Oracle@wdatest11:~/app/admin/wdadb/adump> lsnrctl status
LSNRCTL for Linux: Version 11.1.0.7.0 - Production on 17-JUN-2014 18:15:47
Copyright (c) 1991, 2008, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=wdatest11)(PORT=1521))) ## 到这里，hang住了，一直没有响应
从其他主机做了个tnsping测试：
oracle@IBlvs02:/u01/app/oracle/11.2/db_1/network/admin> tnsping wdatest
TNS Ping Utility for Linux: Version 11.2.0.3.0 - Production on 17-JUN-2014 17:53:20
Copyright (c) 1997, 2011, Oracle. All rights reserved.
Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.121.134)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = wdadb)))
OK (14760 msec) ## 可见响应也是非常慢的。
oracle@IBlvs02:/u01/app/oracle/11.2/db_1/network/admin> tnsping wdatest
TNS Ping Utility for Linux: Version 11.2.0.3.0 - Production on 17-JUN-2014 17:54:20
Copyright (c) 1997, 2011, Oracle. All rights reserved.
Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.121.134)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = wdadb))) ## 这里也是hang住，一直没有响应
最后检查DNS配置时，发现有：
wdatest11:~ # cat /etc/resolv.conf
nameserver 211.141.90.68
系统配置有DNS，这是内网主机，根本用不到DNS，所以把这个DNS去掉后恢复正常。
其实可以考虑开启listener的trace进行查看的。
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