Mining of Massive Datasets - This is a very interesting book which covers many topics in Big Data including Map-Reduce, Recommendation Systems, Mining Social-Network Graphs, Dimensionality Reduction and Large-Scale Machine Learning. I am currently in the 2nd chapter, but found lot of interesting things related to Map-Reduce such as modeling relation algebra using Map-Reduce which is really interesting. Those who are interested in large scale data mining can also follow the free online course from the authors of this book.
Visualizing MNIST: An Exploration of Dimensionality Reduction - This is also a really interesting post about dimensionality reduction in the context of machine learning. The post is well written, even someone not familiar with machine learning, deep learning and dimensionality reduction can read and understand underlying concepts with the help of awesome visualization you will find there.
Translating SQL into the Relational Algebra - Talks about basic concepts of translating SQL to Relation Algebra. If you are new to concepts of SQL to Relation Algebra translation, this document contains brief descriptions, examples and corner cases about most of the translation tasks such as translating subqueries and joins.