业务突然反馈写失败，报错：Lost connection to MySQL server during query。读没有问题 检查proxysql报如下日志： 2019-04-28 16:53:06 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1290, The MySQL server is running with the -- read-only option so it cannot execute this statement 2019-04-28 16:53:06 MySQL_Session.cpp:95:kill_query_thread(): [WARNING] KILL CONNECTION 2740507 on 10.x.x.87:3306 2019-04-28 16:54:06 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1290, The MySQL server is running with the -- read-only option so it cannot execute this statement 2019-04-28 16:54:06 MySQL_Session.cpp:95:kill_query_thread(): [WARNING] KILL CONNECTION 2737976 on 10.x.x.87:3306 2019-04-28 16:55:29 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1290, The MySQL server is running with the -- read-only option so it cannot execute this statement 2019-04-28 16:55:29 MySQL_Session.cpp:95:kill_query_thread(): [WARNING] KILL CONNECTION 2796368 on 10.x.x.87:3306 2019-04-28 16:59:07 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1054, Unknown column 'date' in 'order clause' 2019-04-28 17:05:10 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1290, The MySQL server is running with the -- read-only option so it cannot execute this statement 2019-04-28 17:05:10 MySQL_Session.cpp:95:kill_query_thread(): [WARNING] KILL CONNECTION 2797386 on 10.x.x.87:3306 2019-04-28 17:06:45 MySQL_Session.cpp:2934:handler(): [WARNING] Error during query on (1,10.x.x.87,3306): 1290, The MySQL server is running with the -- read-only option so it cannot execute this statement 2019-04-28 17:06:45 MySQL_Session.cpp:95:kill_query_thread(): [WARNING] KILL CONNECTION 2797798 on 10.x.x.87:3306 意思就是有写操作到从了，由于从是只读的，写失败kill了连接，导致报lost connection to mysql during query. 为什么写会路由到从呢？ 先看路由配置：  读写分离路由是没有问题的，通过日志看到有set autocommit=0这样开启事务。检查配置发现： mysql-forward_autocommit=false mysql-autocommit_false_is_transaction=false 这两个设置为false，会导致set autocommit = 0不会开启事务，所以如果set autocommit=0后，先select，再有写操作，有可能会导致写到从库（也存在bug）。 如下有issue类似问题链接： - [Write Queries were routing to read hostgroup](https://github.com/sysown/proxysql/issues/1658) - [When mysql-forward_autocommit=true , treat autocommit=0 as a transaction](https://github.com/sysown/proxysql/issues/1155) - ["set autocommit = 0" is not a transaction](https://github.com/sysown/proxysql/issues/1716) 所以建议将如下配置为true: mysql-forward_autocommit=true mysql-autocommit_false_is_transaction=true 还有写请求会落到从库的，有可能是路由规划配置有问题，如用match_pattern匹配，就有可能在sql换行就匹配不到的情况。最好是用match_digest来匹配。 它们的区别是： match_pattern ：原始的sql进行正则匹配 match_digest ：签名后的sql进行正则匹配，如stats_mysql_query_digest里的sql ###总结： ProxySQL是MySQL中件间中比较优秀的，但在使用上还需要多注意，尽量简单使用，理解配置产生的效果及影响。