循环中的迭代次数(Number of iterations in a loop)

 大部分真正大规模的网络媒体资源都使用分布式键值存储。 也就是说，3500万是大的，但并不那么大。 对于大多数现代数据库，您主要的两个扩展问题应该是吞吐量，并且当没有单个盒子可以包含整个数据库时会发生什么。 对于您选择使用的任何数据库，这两个问题都可以在一定程度上得到解决。 （缓存，复制，分片等） 
 
 直到你不能再使用MySQL。 那时，无论如何你都应该在面团中滚动，现在你有一个非常理想的问题。 

Most of the truly large scale web properties use a distributed key-value store. That said, 35 million is large, but not that large. With most modern databases, your main two scaling worries should be throughput and what happens when no single box can contain your entire database anymore. And both of these problems can be solved to some degree for any database you choose to use. (Caching, replication, sharding, etc.)
 
Use MySQL until you can't anymore. At that point, you ought to be rolling in dough anyways and you now have a very desirable problem.