<span style="line-height:normal;white-space:normal;background-color:#FFFFFF;font-family:'Microsoft YaHei';font-size:small;"><span style="font-size:14px;">监听器是Oracle基于服务器端的一种网络服务，主要用于监听客户端向数据库服务器端提出的连接请求。Oracle官方对其的定义为：A process that listens for incoming client connection requests and manages network traffic to the database.</span><br /> <span style="font-size:14px;">本地服务名是Oracle客户端网络配置的一种，另外还有Oracle名字服务器(Oracle Names Server)等。</span><br /> </span> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:14px;">客户端可以通过监听来和数据库服务器进行交互，如果我们是用tnsping来测试，并且返回正常，是否意味着数据库可用？答案是否定的。</span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:14px;">1. 如下监听是正常启动：</span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><img src="http://img.blog.csdn.net/20150807101910618?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" _xhe_src="http://img.blog.csdn.net/20150807101910618?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" style="max-width:98%;" /></span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:14px;">2. 此时关闭数据库：</span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><img src="http://img.blog.csdn.net/20150807101942266?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" _xhe_src="http://img.blog.csdn.net/20150807101942266?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" style="max-width:98%;" /><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:14px;">3. 从客户端执行tnsping，显示是连接正常。</span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><img src="http://img.blog.csdn.net/20150807102001470?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" _xhe_src="http://img.blog.csdn.net/20150807102001470?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" style="max-width:98%;" /><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:small;"><br /> </span> </p> <p style="margin-top:4px;margin-bottom:4px;padding-top:2px;padding-bottom:2px;font-family:Arial, Helvetica, sans-serif;line-height:normal;white-space:normal;background-color:#FFFFFF;"> <span style="font-family:'Microsoft YaHei';font-size:14px;">由此我们可以看到，tnsping只是验证了客户端和数据库服务器的监听端口之间的通路是好的，但并未意味着数据库服务是可用的，因为客户端和Oracle服务器交互是通过Oracle server服务器进程来进行的，私有内存空间即是PGA，所以有时候我们做运维检测，tnsping不能代表Oracle数据库可用，可以用sqlplus真正执行一条语句(select sysdate from dual)才行。</span> </p>