c++ - MySQL 服务器已经消失

Question

这是我的代码片段:

query.next();
qDebug()<<query.lastError();
qlonglong res=query.value(0).toLongLong();
qDebug()<<query.lastError();

和我有的相应日志:

Debug: QSqlError(2006, "QMYSQL: Unable to execute query", "MySQL server has gone away") 
Warning: QSqlQuery::value: not positioned on a valid record
Debug: QSqlError(2006, "QMYSQL: Unable to execute query", "MySQL server has gone away")

通常我的程序工作正常(它在服务器上工作并接受来自客户端的连接)，但每天早上当我尝试连接它时，我都会收到上面的消息。

MySQL 服务器可能有什么问题？

Answer 1

来自MySQL Manual :

The most common reason for the MySQL server has gone away error is that the server timed out and closed the connection.

...

By default, the server closes the connection after eight hours if nothing has happened. You can change the time limit by setting the wait_timeout variable when you start mysqld.

...

If you have a script, you just have to issue the query again for the client to do an automatic reconnection. This assumes that you have automatic reconnection in the client enabled (which is the default for the mysql command-line client).

参见 this manual page有关此错误的更多详细信息。