title: Out of core connected components algorithms
body: <p>I have 4,000,000,000 (four billion) edges for an undirected graph. They are represented in a large text file as pairs of node ids.  I would like to compute the connected components of this graph. Unfortunately, once you load in the node ids with the edges into memory this takes more than the 128GB of RAM I have available.  </p>
  
  <p>Is there an out of core algorithm for finding connected components that is relatively simple to implement? Or even better, can be it cobbled together with Unix command tools and existing (python) libraries?</p>