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As we can see, the compute method is calling 3 other methods.
In the createSumVertex method we can see the creation of a new vertex with ID the text sum and value 0.
Later on, in sendAllValuesToSumAndRemove we can see that each vertex that runs this method is deleting itself by running this.remove();.
In the end, calculateSum is called that summarizes the values of all vertices in the sum vertex. The interesting part of the last method is that also adding the number of input vertices this.getPeer().getCounter(GraphJobCounter.INPUT_VERTICES).getCounter() and the current number of vertices that exist on the running superstep this.getNumVertices().
Implementation Details
addVertex --> create new vertex instance --> find a proper BSP peer to host the new vertex through the partitioner --> serialize the new vertex and send it as a map message to the peer --> the destination peer, on the new superstep, during executing parseMessages method, will receive the serialized object ---> GraphJobRunner::addVertex will add the new vertex in the data structure that keeps all vertices (VerticesInfo)
meanwhile
in step 4 the peer, hosting the vertex where the addVertex method is invoked, is increasing a local variable by the number of new vertices added. This local variable is collected from all peers from aggregators and results in changing the total number of vertices in all peers.
The GraphJobRunner class, contains the major steps for the graph computation. It starts with an initial setup, where the vertexes are loaded to memory, then there is the main computation loop, where the supersteps occur, and in the end there is the cleanup, where of the graph and the results are written to HDFS.
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