阿里巴巴DBA,原去哪儿网DBA。专注于MySQL源码研究、DBA运维、CGroup虚拟化及Linux Kernel源码研究等。 github:https://github.com/HengWang/ Email:king_wangheng@163.com 微博 :@王恒-Henry QQ :506437736
分类: Mysql/postgreSQL
2013-02-28 11:57:44
目的
为了理解MySQL在执行大SQL时,对执行CTRL+C产生的疑惑,本文通过实验测试和源码分析两个方面,对MySQL处理CTRL+C的详细过程进行分析和讲解,从而解除DBA及开发人员对CTRL+C的误解。
测试
首先,基于线上数据库版本,分别使用MySQL客户端版本5.5.20和5.0.77进行实验测试,一方面排除不同数据库客户端版本造成的差异,另一方面,深入了解不同版本执行CTRL+C产生的差异。
MySQL客户端5.5.20
使用MySQL客户端5.5.20在Session1中执行select sleep(100)语句,在Session2中执行show processlist语句;然后在Session1中执行CTRL+C,在Session中执行show processlist语句,查看当前连接的线程。执行的图如下所示:
Session1:
mysql> select sleep(100); Ctrl-C -- sending "KILL QUERY 153779" to server ... Ctrl-C -- query aborted. ERROR 2013 (HY000): Lost connection to MySQL server during query |
Session2:
mysql> show processlist;
mysql> show processlist; |
从以上结果来看,Session1中执行select操作时,Session2中可以查看该连接正在执行,在Session1中执行CTRL+C时,客户端向服务器端发送KILL QUERY
MySQL客户端5.0.77
使用客户端5.0.77执行同样的操作,执行CTRL+C后,观察执行的差异性。具体如下表中所示:
Session1:
mysql> select sleep(100); Query aborted by Ctrl+C +------------+ | sleep(100) | +------------+ | 1 | +------------+ |
Session2:
mysql> show processlist;
mysql> show processlist;
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+-------------------+-----------+---------------+-----------+
| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+-------------------+-----------+---------------+-----------+
| 153783 | heng.wang | 127.0.0.1:45807 | NULL | Query | 3 | User sleep | select sleep(100) | 0 | 0 | 1 |
| 153784 | heng.wang | 127.0.0.1:45809 | NULL | Query | 0 | NULL | show processlist | 0 | 0 | 1 |
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+-------------------+-----------+---------------+-----------+
2 rows in set (0.00 sec)
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+------------------+-----------+---------------+-----------+
| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+------------------+-----------+---------------+-----------+
| 153783 | heng.wang | 127.0.0.1:45807 | NULL | Sleep | 10 | | NULL | 1 | 0 | 1 |
| 153784 | heng.wang | 127.0.0.1:45809 | NULL | Query | 0 | NULL | show processlist | 0 | 0 | 1 |
+--------+-------------+-----------------+------+-------------+---------+-----------------------------------------------------------------------------+------------------+-----------+---------------+-----------+
2 rows in set (0.00 sec)
从以上结果可知,Session1上执行select时,Session2中建立查询连接;在Session1中执行CTRL+C时,显示Query被终止,并且返回执行的错误结果。在Session2中可知,连接的线程仍然存在,但是Query被终止,只是保持连接。
源码分析
为了更进一步对以上测试进行确认,查看MySQL源码进行进一步的求证,同样基于MySQL的5.5.20和5.0.77两个版本进行验证。具体如下:
MySQL 5.5.20源码
MySQL客户端主函数main中,信号函数在源码文件client/mysql.cc:1163,源码如下所示:
signal(SIGINT, handle_sigint); // Catch SIGINT to clean up |
信号处理函数handle_sigint在client/mysql.cc:1291,源码如下所示:
sig_handler handle_sigint(int sig) { char kill_buffer[40]; MYSQL *kill_mysql= NULL; /* terminate if no query being executed, or we already tried interrupting */ if (!executing_query || (interrupted_query == 2)) { tee_fprintf(stdout, "Ctrl-C -- exit!\n"); goto err; } kill_mysql= mysql_init(kill_mysql); if (!mysql_real_connect(kill_mysql,current_host, current_user, opt_password, "", opt_mysql_port, opt_mysql_unix_port,0)) { tee_fprintf(stdout, "Ctrl-C -- sorry, cannot connect to server to kill query, giving up ...\n"); goto err; } interrupted_query++; /* mysqld < 5 does not understand KILL QUERY, skip to KILL CONNECTION */ if ((interrupted_query == 1) && (mysql_get_server_version(&mysql) < 50000)) interrupted_query= 2; /* kill_buffer is always big enough because max length of %lu is 15 */ sprintf(kill_buffer, "KILL %s%lu", (interrupted_query == 1) ? "QUERY " : "", mysql_thread_id(&mysql)); tee_fprintf(stdout, "Ctrl-C -- sending \"%s\" to server ...\n", kill_buffer); mysql_real_query(kill_mysql, kill_buffer, (uint) strlen(kill_buffer)); mysql_close(kill_mysql); tee_fprintf(stdout, "Ctrl-C -- query aborted.\n"); return; err: #ifdef _WIN32 mysql_thread_end(); return; #else mysql_end(sig); #endif } |
从以上源码可知,MySQL客户端在捕获信号后,将KILL QUERY
MySQL 5.0.77源码
MySQL客户端主函数main中,信号函数在源码文件client/mysql.cc:1150。源码如下所示:
signal(SIGINT, mysql_sigint); // Catch SIGINT to clean up |
信号处理函数mysql_sigint在源码文件client/mysql.cc:1214,源码如下所示:
sig_handler mysql_sigint(int sig) { char kill_buffer[40]; MYSQL *kill_mysql= NULL; /* terminate if no query being executed, or we already tried interrupting */ if (!executing_query || interrupted_query++) goto err; kill_mysql= mysql_init(kill_mysql); if (!mysql_real_connect(kill_mysql,current_host, current_user, opt_password, "", opt_mysql_port, opt_mysql_unix_port,0)) goto err; /* kill_buffer is always big enough because max length of %lu is 15 */ sprintf(kill_buffer, "KILL /*!50000 QUERY */ %lu", mysql_thread_id(&mysql)); mysql_real_query(kill_mysql, kill_buffer, strlen(kill_buffer)); mysql_close(kill_mysql); tee_fprintf(stdout, "Query aborted by Ctrl+C\n"); return; err: #ifdef _WIN32 mysql_thread_end(); return; #else mysql_end(sig); #endif } |
通过以上源码可知,MySQL客户端捕获信号后,向服务器端发送KILL /*!50000 QUERY */
基于以上两个版本处理的源码可知,MySQL客户端一定会捕获CTRL+C信号,并对该信号进行处理。而对于不同版本的客户端,由于发送命令的不同,导致MySQL服务器端执行结果有所不同。
结论
通过以上测试和源码分析可知,MySQL客户端肯定会捕获CTRL+C信号,并对信号进行处理。不同的是,在MySQL 5.5.20版本的客户端中执行时,服务器端执行KILL QUERY
此外,对于update、delete数据更新操作[1],CTRL+C会将执行的操作标记为KILLED状态,然后执行回滚操作。因此,不会因为CTRL+C操作,导致数据变脏。
参考资料:
1、KILL Syntax:http://dev.mysql.com/doc/refman/5.5/en/kill.html
king_wangheng2013-04-09 22:35:26
zhangshengdong:有点疑问:
kill <id>
和kill query <id>两者是不同概念的
是不同的概念,kill <id>是关闭线程连接;kill query <id>是关闭query,连接保持。这是不同版本对CTRL+C的不同处理策略!
回复 | 举报