向Mysql插入数据越来越慢

我需要每分钟插入388个数据到本地数据库。首先，当表是空的，我只需要5秒插入到数据库。

但是当表变大时，当行数达到1,026,558时，程序效率减慢到1分钟以上。

， CPU使用率为100%。这是不寻常的。

下面是我的代码:

public static void dataToDB(String[] routeIDArray,String[] levelArray,String[] valueArray,String[] travelTimeArray, int amountOfData)
    {
        MySqlConnection con = new MySqlConnection(connStr);
        MySqlCommand cmd = null;
        MySqlDataReader rdr = null;
        String sqlCmd, updateSqlCmd = "UPDATE `datetimetable` SET ";
        for(int counter = 0; counter < amountOfData; counter++)
        {
            sqlCmd = "ALTER TABLE `datetimetable` ADD COLUMN IF NOT EXISTS `" + routeIDArray[counter] + "` INT NULL;"
                + "INSERT INTO `roadvalue`.`data` (`level`,`value`,`traveltime`) VALUES ("
                + levelArray[counter] + ","
                + valueArray[counter] + ","
                + travelTimeArray[counter] + ");"
                + "SELECT LAST_INSERT_ID() FROM `data`;";
            cmd = new MySqlCommand(sqlCmd, con);
            con.Open();
            rdr = cmd.ExecuteReader();
            rdr.Read();
            updateSqlCmd += "`" + routeIDArray[counter] + "` = " + rdr[0] + ",";
            rdr.Close();
        }
        updateSqlCmd = updateSqlCmd.TrimEnd(',');
        updateSqlCmd += " WHERE EXISTS (SELECT * WHERE dateTime = '" + dateTime.ToString("yyyy-MM-dd HH:mm:00") + "');";
        cmd = new MySqlCommand(updateSqlCmd, con);//update data key to datetimetable
        cmd.ExecuteNonQuery();
        Console.WriteLine("Done.");
        con.Close();
    }
    public static void checkDateTimeExisted()
    {
        MySqlConnection con = new MySqlConnection(connStr);
        MySqlCommand cmd;
        String sqlCmd;
        sqlCmd = "INSERT INTO `datetimetable` (`dateTime`) SELECT * FROM (SELECT '" + dateTime.ToString("yyyy-MM-dd HH:mm:00")
                     + "') AS tmp WHERE NOT EXISTS(SELECT `dateTime` FROM `datetimetable` WHERE `dateTime` = '" + dateTime.ToString("yyyy-MM-dd HH:mm:00") + "') LIMIT 1; ";
            con.Open();
            cmd = new MySqlCommand(sqlCmd, con);
            cmd.ExecuteNonQuery();
            con.Close();
    }

Mysql引擎是InooDB，表"data"有一个Auto_Increment主键，表"dateschedule"有一个Auto_Increment主键和一个不重复的datetime作为索引。

我做错了什么?

INSERT IGNORE INTO datetimetable
    (datetime)
    VALUE
    ('...');