How to compute Fibonacci sequence in SQL
Inspired and simplified from a set of slides on using RDBMS for storing, managing, and querying graphs: with recursive fib(i,j) as ( select 0,1 union all select j, i+j from fib where j
Immerse yourself in the social graph of your email
Which files has a *nix process opened?
To list all files that are opened by a *nix process with a given pid, say 42, use the lsof command: (sudo) lsof -p 42 Of course, a process may have many files open. To list only files that have…
How long is the Doom Loop cycle currently?
Take a look at this Chomsky presentation, time it around 46:30. It seems that the most rational prediction would be that we are heading for another financial crisis, since financial systems are running a quote “Doom Loop”: Make huge gambles,…
Must remember to salt my hashes
While a sha-256 hash may seem unbreakable, for many input strings it takes seconds to crack. If you don’t believe me, try the following or simply read this webpage: $ python >>> import hashlib >>> print hashlib.sha256(‘megabrain’).hexdigest() f53c51616f4c7943a4117afa1d0ba193f9af901c6ce175a2207a594e71c98ef5 Go to…
Docker on Ubuntu VM running on Mac using Vagrant
Docker allows you to develop, ship and run any application, anywhere. The metaphor is that of the standard shipping container that fits on any ship, can be handled by any crane, and loaded onto any train or truck. In a…
Running Ubuntu on Mac with Vagrant
Vagrant is cool: Vagrant provides easy to configure, reproducible, and portable work environments built on top of industry-standard technology and controlled by a single consistent workflow to help maximize the productivity and flexibility of you and your team. Furthermore: Vagrant…
Starting a web server and other PHP tricks
Start PHP webserver (in current directory): php -S localhost:8080 # starts http server on port 8080 Start PHP prompt (with illustrating example):
Screen capturing with PhantomJS
PhantomJS is a headless browsers that you can use, e.g. to test web UIs and to screen capture webpages. I will focus on the last use case. Since PhantomJS knows how to execute Javascript, it can create a screen shot…
Twitter HyperLogLog monoids in Spark
Want to count unique elements in a stream without blowing up memory? In more specific words, do you want to use a HyperLogLog counter in Spark? Until today, I’d never heard the word “monoid” before. However, Twitter Algebird is a…