• To     reduce the number of I/Os performed when you create an index, first sort     the data by the key variable. Then to improve performance, maintain the     data file in sorted order by the key variable. If the data file has more     than one index, sort the data by the most frequently used key variable.
• 求大神解答，为啥 pre sorted 好的数据，在创建index时，会降低I/O Cost？？？