使用 MySQL 時遇到 Can't connect to MySQL server 問題…

如果你的程式使用了太多的 mysqlpp::Connection 物件，會導致你的系統殘存太多的 TCP Connection 在 TIME_WAIT，一旦系統有超過可使用的數量，則會導致無法在建立連線，進而導致 mysqlpp::Connection 無法連線到 mysql 伺服器。

針對此問題，mysql 官方手冊有提到如何對應：

2 Connection to MySQL Server Failing on Windows

When you're running a MySQL server on Windows with many TCP/IP connections to it, and you're experiencing that quite often your clients get a Can't connect to MySQL server error, the reason might be that Windows doesn't allow for enough ephemeral (short-lived) ports to serve those connections. ... 閱讀全文

跟著文章的方式修改 reg 註冊表，重開機後即可增加連線數量。