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Can’t connect to MySQL server有关linux tcp连接优化

 

最近有2台web机器链接mysql有时会出现Can’t connect to MySQL server的情况,查看exception日志:

 

如下:

 

[message:protected] => SQLSTATE[HY000] [2003] Can’t connect to MySQL server on ‘192.168.1.248′(99)

 

1):问题描述:

 

2台web机器,只有其中一台出现该exception,另外一台无此问题;

 

exception logs: Can’t connect to MySQL server on ‘*.*.*.*’ (99)

 

2):问题排查:

 

1、查看mysql的variables,status:

max_connect_errors = 50000max_connections = 1000max_user_connections = 200max_connect_errors = 50000max_connections = 1000max_user_connections = 200

 

 

2、ulimit -a:

 

3、查看netstat -anp

 

查看问题机器的netstat -anp,发现大部分都是TIME_WAIT,怀疑是tcp的问题;

 

将近有3万的网络套接字,此时CPU也耗尽,导致这么多的TCP/IP连接CPU处理不过来,而使部分TCP/IP连接超时或处理失败

 

3、OS:

 

more /etc/sysctl.conf:

 

net.ipv4.tcp_syncookies = 1

 

新的连接可以重新使用TIME-WAIT套接字

 

net.ipv4.tcp_tw_reuse=1

 

启动TIME-WAIT套接字状态的快速循环功能

 

net.ipv4.tcp_tw_recycle=1

 

套接字关闭时,保持FIN-WAIT-2状态的时间

 

net.ipv4.tcp_fin_timeout=30

 

对于所有协议的队列,设置最大系统发送缓存(wmen)和接收缓存(rmem)到8M

 

net.core.wmem_max=8388608

 

net.core.rmem_max=8388608

 

让参数生效。

 

3):问题原因:

 

报错”Can’t connect to MySQL server on ‘*.*.*.*’ (99) ” 参考MySQL Client端错误代码说明:错误代码为99,99的含义:$perror 99 OS error code  99:  Cannot assign requested address 这是一个本地OS的抛错,表示无法分配本地地址资源(应该是端口),socket无法创建

 

” Cannot assign requested address”,多半是由于客户端请求过于频繁,而Server端练级关闭后本地暂时处于TIME_WAIT,所以暂时端口都不可用导致。因此修改下OS参数就ok了

 

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