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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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