MySQL索引背后的数据结构及算法原理, http://www.codinglabs.org/html/theory-of-mysql-index.html
解读Cardinality Estimation算法（第一部分：基本概念）, http://blog.codinglabs.org/articles/algorithms-for-cardinality-estimation-part-i.html
解读Cardinality Estimation算法（第二部分：Linear Counting）, http://blog.codinglabs.org/articles/algorithms-for-cardinality-estimation-part-ii.html
解读Cardinality Estimation算法（第三部分：LogLog Counting）, http://blog.codinglabs.org/articles/algorithms-for-cardinality-estimation-part-iii.html
解读Cardinality Estimation算法（第四部分：HyperLogLog Counting及Adaptive Counting）, http://blog.codinglabs.org/articles/algorithms-for-cardinality-estimation-part-iv.html
https://highlyscalable.wordpress.com/2012/05/01/probabilistic-structures-web-analytics-data-mining/