我不太喜欢一直把技术当黑箱使用，需要花时间理解底层原理。参考资料：

http://coding-geek.com/how-databases-work/

http://blog.jobbole.com/100349/

You can google by yourself “how does a relational database work” to see how few results there are. Moreover, those articles are short.

http://coding-geek.com/how-does-a-hashmap-work-in-java/