At 2014-09-16 10:55:37 +0200, Yifan LI <[email protected]> wrote: > - from [1], and my understanding, the existing inactive feature in graphx > pregel api is “if there is no in-edges, from active vertex, to this vertex, > then we will say this one is inactive”, right?
Well, that's true when messages are only sent forward along edges (from the source to the destination) and the activeDirection is EdgeDirection.Out. If both of these conditions are true, then a vertex without in-edges cannot receive a message, and therefore its vertex program will never run and a message will never be sent along its out-edges. PageRank is an application that satisfies both the conditions. > For instance, there is a graph in which every vertex has at least one > in-edges, then we run static Pagerank on it for 10 iterations. During this > calculation, is there any vertex would be set inactive? No: since every vertex always sends a message in static PageRank, if every vertex has an in-edge, it will always receive a message and will remain active. In fact, this is why I recently rewrote static PageRank not to use Pregel [3]. Assuming that most vertices do have in-edges, it's unnecessary to track active vertices, which can provide a big savings. > - for more “explicit active vertex tracking”, e.g. vote to halt, how to > achieve it in existing api? > (I am not sure I got the point of [2], that “vote” function has already been > introduced in graphx pregel api? ) The current Pregel API effectively makes every vertex vote to halt in every superstep. Therefore only vertices that receive messages get awoken in the next superstep. Instead, [2] proposes to make every vertex run by default in every superstep unless it votes to halt *and* receives no messages. This allows a vertex to have more control over whether or not it will run, rather than leaving that entirely up to its neighbors. Ankur >> [1] >> http://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.graphx.Pregel$ >> [2] https://github.com/apache/spark/pull/1217 [3] https://github.com/apache/spark/pull/2308 --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
