大量的 TIME_WAIT 解决办法
netstat -an192.168.12.13:3306????? 192.168.12.12:30443????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30444????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30445????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30446????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30447????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30448????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30449????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30450????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30451????? TIME_WAIT192.168.12.13:3306????? 192.168.12.12:30452????? TIME_WAIT... ...????? 根据TCP协议定义的3次握手断开连接规定,发起socket主动关闭的一方 socket将进入TIME_WAIT状态,TIME_WAIT状态将持续2个MSL(Max Segment Lifetime),在Windows下默认为4分钟,即240秒,TIME_WAIT状态下的socket不能被回收使用. 具体现象是对于一个处理大量短连接的服务器,如果是由服务器主动关闭客户端的连接,将导致服务器端存在大量的处于TIME_WAIT状态的socket, 甚至比处于Established状态下的socket多的多,严重影响服务器的处理能力,甚至耗尽可用的socket,停止服务. TIME_WAIT是TCP协议用以保证被重新分配的socket不会受到之前残留的延迟重发报文影响的机制,是必要的逻辑保证.
??????在HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters,添加名为TcpTimedWaitDelay的
DWORD键,设置为60,以缩短TIME_WAIT的等待时间?登陆到web服务器(linux)：???????? netstat -ae |grep mysql???? tcp??????? 0????? 0 aaaa:53045?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53044?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53051?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53050?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53049?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53048?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53055?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53054?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53053?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53052?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53059?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53058?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53057?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53056?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53063?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53062?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53061?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53060?????????????? 192.168.12.3:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53067?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53066?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53065?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53064?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa53071?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53070?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
tcp??????? 0????? 0 aaaa:53069?????????????? 192.168.12.13:mysql?????????? TIME_WAIT?? root?????? 0
发现系统存在大量TIME_WAIT状态的连接，通过调整内核参数解决，vi /etc/sysctl.conf
编辑文件，加入以下内容：net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_fin_timeout = 30?然后执行?/sbin/sysctl -p?让参数生效。?net.ipv4.tcp_syncookies = 1?表示开启SYN Cookies。当出现SYN等待队列溢出时，启用cookies来处理，可防范少量SYN攻击，默认为0，表示关闭；
net.ipv4.tcp_tw_reuse = 1?表示开启重用。允许将TIME-WAIT sockets重新用于新的TCP连接，默认为0，表示关闭；
net.ipv4.tcp_tw_recycle = 1?表示开启TCP连接中TIME-WAIT sockets的快速回收，默认为0，表示关闭。
net.ipv4.tcp_fin_timeout?修改系統默认的 TIMEOUT 时间?修改之后，再用netstat -ae|grep mysqltcp??????? 0????? 0 aaaa:50408?????????????? 192.168.12.13:mysql?????????? ESTABLISHED nobody???? 3224651
tcp??????? 0????? 0 aaaa:50417?????????????? 192.168.12.13:mysql?????????? ESTABLISHED nobody???? 3224673
tcp??????? 0????? 0 aaaa:50419?????????????? 192.168.12.13:mysql?????????? ESTABLISHED nobody???? 3224675
?????? 发现大量的TIME_WAIT?已不存在，mysql进程的占用率很快就降下来的，各网站访问正常！！?????? 以上只是暂时的解决方法，最后仔细巡查发现是前天新上线的一个系统，程序代码中没有使用mysql.colse()，才导致大量的mysql? TIME_WAIT ?
