An illustration of an execution of a single source shortest paths algorithm in Giraph. The input is a chain graph with three vertices (black) and two edges (green). The values of edges are 1 and 3 respectively. The algorithm computes distances from the leftmost vertex. The initial values of vertices are 0, ∞ and ∞ (top row). Distance upper bounds are sent as messages (blue), resulting in updates to vertex values (successive rows going down). The execution lasts three supersteps (separated by red lines).