对于这个服务器,我创建了单个数据库实例,我准备了所有的数据库查询.

但是对于更多的TcpClient,我会不断得到异常：

An exception of type MySql.Data.MySqlClient.MysqLException occurred
in MysqL.Data.dll but was not handled in user code

Additional information: There is already an open DataReader associated
with this Connection which must be closed first.

如果我理解正确,则不能再有一个数据库查询在时间上是多个异步客户端的问题.

所以我只是在这样的查询中添加了锁,一切似乎都很好.

// One MysqLConnection instance for whole program.

   lock (thisLock)
   {
    var cmd = connection.CreateCommand();

    cmd.CommandText = "SELECT Count(*) FROM logins WHERE username = @user AND password = @pass";
    cmd.Parameters.AddWithValue("@user",username);
    cmd.Parameters.AddWithValue("@pass",password);

    var count = int.Parse(cmd.ExecuteScalar().ToString());
    return count > 0;
}

我也尝试使用这种方法,它为每个查询创建新的连接,如从SO社区的人那里提到的,但是这种方法比锁更慢：

using (MysqLConnection connection = new MysqLConnection(connectionString))
    {
        connection.Open();   // This takes +- 35ms and makes worse performance than locks

        using (MysqLCommand cmd = connection.CreateCommand())
        {
            cmd.CommandText = "SELECT Count(*) FROM logins WHERE username = @user AND password = @pass";
            cmd.Parameters.AddWithValue("@user",username);
            cmd.Parameters.AddWithValue("@pass",password);

            int count = int.Parse(cmd.ExecuteScalar().ToString());
            return count > 0;
        }
    }

我使用秒表来测试这种方法和查询,一个连接与锁是在 – 20ms执行,这是 – 只有网络的延迟,但使用它是 – 55ms,因为.Open()方法 – 35ms.

为什么很多人使用使用方法,如果性能更差？还是我做错了？