今天早上一上班,有同事就反映公司好几个网站都打不开,登陆数据库
服务器(windows),发现很卡,于是重启了下服务器,进入系统后,没过一会问题依旧,查看了下系统进程,发现mysql占用率达到
99%,可以肯定的是mysql连接出现问题:
netstat -an
192.168.12.13:3306 192.168.12.12:30443 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30444 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30445 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30446 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30447 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30448 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30449 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30450 TIME_WAIT
192.168.12.13:3306 192.168.12.12:30451 TIME_WAIT
192.168.12.13:3306 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 mysql
tcp 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
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