保持单个查询快速的一些技术包括将数据拆分到多个表中。当表的数量达到数千甚至数百万时，处理所有这些表的开销会成为一个新的性能考量因素。Some techniques for keeping individual queries fast involve splitting data across many tables. When the number of tables runs into the thousands or even millions, the overhead of dealing with all these tables becomes a new performance consideration.