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MySQL连接hang住问题分析

时间:2021-07-01 10:21:17 帮助过:28人阅读

Linux c多线程连接mysql数据库,每次都是短连接,操作完后就释放连接,有时候会出现mysql_real_connect挂住的现象,挂住超时mysql

【问题现象】:

1. Linux c多线程连接mysql数据库,每次都是短连接,操作完后就释放连接,有时候会出现mysql_real_connect挂住的现象

2. 挂住超时mysql_real_connect返回后报错如下:Lostconnection to MySQL server at 'reading initial communication packet', systemerror: 104,返错后线程号没变,会继续往下运行

【初步原因分析】:

1. mysql_real_connect连接数据库, 没有显式调用超时时间,重连什么的,,使用的默认值:

2. 昨天拿c mysqlclient的源码进行了分析测试,发现以下几个配置项的默认值(如果调mysql_real_connect之前没有设置任何属性,mysql client端的机器上/etc/my.cnf也没有配置)如下:

connect_timeout = 0

read_timeout = 0

write_timeout = 0

reconnect = 0 //1表示自动重连

所以这些参数是需要显式设置的。

{net = {vio = 0x7b8f150, options = {connect_timeout = 0, read_timeout = 0, write_timeout = 0,}

3. Mysqlclient中报错的代码如下(与服务端连接建立后,读解析包的时候失败了):

/*

Part 1: Connection established, read and parse first packet

*/

if ((pkt_length=cli_safe_read(mysql)) == packet_error)

{

if (mysql->net.last_errno == CR_SERVER_LOST)

set_mysql_extended_error(mysql, CR_SERVER_LOST, unknown_sqlstate,

ER(CR_SERVER_LOST_EXTENDED),

"reading initial communication packet",

errno);

fprintf(myfp,"%s after cli_safe_read packet_error \n",cur_time());

goto error;

}

线程阻塞时抓到的堆栈如下:


#0 0x0000003ebe0c5f3b in read () from /lib64/libc.so.6

#1 0x00007f240dd91430 in vio_read () from /usr/lib/libmysql.so.16.0.0

#2 0x00007f240dcf9b05 in my_real_read () from /usr/lib/libmysql.so.16.0.0

#3 0x00007f240dcf9e38 in my_net_read () from /usr/lib/libmysql.so.16.0.0

#4 0x00007f240dcec396 in cli_safe_read () from /usr/lib/libmysql.so.16.0.0

#5 0x00007f240dceea17 in mysql_real_connect () from /usr/lib/libmysql.so.16.0.0

linux

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