Thank you all for the replies. I think Kaushik has the easiest solution for me. I'll give that a try.
Avery: I want to the vertices to re-activate when they receive a new message, unless all vertices have voted to halt that iteration. So not reactivating after voting to halt would not solve this problem. Thanks, Nick On Aug 4, 2012, at 1:49 PM, Avery Ching wrote: I think it would be pretty straightforward to add an option to not re-activate a halted vertex on new messages. Would that satisfy your issue Nick? Avery On 8/4/12 2:42 AM, Sebastian Schelter wrote: Hi Nick, I think you are running into the issue that vertex activation/scheduling and data transfer are not separated in the Pregel/Giraph model. I ran into the same problem when trying to implement Adaptive PageRank on Giraph. I think the problem comes from the vast generality of Pregel's BSP model: vertices can send any kind of message to any other vertex. However, in a lot of algorithms, vertices only send their state to their neighbors. Other platforms such as GraphLab separate activation/scheduling from messaging, in this system a vertex can only schedule its neighbors and once one of the neighbors is invoked, it can read the state of its direct neighbors. I think that the Pregel model is simply not suited for such algorithms (unfortunately), let me know if you find a clever workaround. Best, Sebastian 2012/8/3 Nick West <nick.w...@benchmarksolutions.com<mailto:nick.w...@benchmarksolutions.com>> Thanks for the reply. Is there an easy modification that I can make to remove condition 2? Can you point me to the code that addresses this? The problem I am facing is the following: At every iteration a non-halted vertex needs messages from all of its neighbors. When deciding to send messages, a given vertex doesn't know if its neighbors will vote-to-halt in the current superstep, thus it must send a message to each of its neighbors. In the case that all vertices have voted to stop, the sending of a messages by any vertex will cause the algorithm to continue, yet in this situation it is desirable to terminate. I have worked out a few solutions that involve either increasing the amount of data a vertex saves each iteration or augmenting the messages sent with additional information, but I think it would be beneficial, and more general, to allow this type of termination instead. Do you have any thoughts on this? Thanks, Nick On Aug 3, 2012, at 10:14 AM, Alessandro Presta wrote: Hi Nick, You are pretty much correct, except that not all vertices need to vote to halt at the same time: some vertices might have voted to halt at a previous superstep and never received any messages after then, in which case they are never reactivated. In other words, I think you can rephrase that as: All vertices are halted after a given superstep No messages were sent in that superstep Hope it helps. Alessandro From: Nick West <nick.w...@benchmarksolutions.com<mailto:nick.w...@benchmarksolutions.com>> Reply-To: "user@giraph.apache.org<mailto:user@giraph.apache.org>" <user@giraph.apache.org<mailto:user@giraph.apache.org>> Date: Friday, August 3, 2012 2:48 PM To: "user@giraph.apache.org<mailto:user@giraph.apache.org>" <user@giraph.apache.org<mailto:user@giraph.apache.org>> Subject: Termination Conditions Excuse me if this is stated somewhere obvious, but I haven't been unable to find it. What are the exact termination criteria for the global algorithm? Reading the documentation on voteToHalt, looking at the Shortest Path Example code, and looking at the results of my own application, these two conditions must both hold for the global BSP algorithm to terminate: 1) All vertices vote to halt in a given superstep 2) No messages are sent in that supersetp Is that correct? Thanks, Nick West Benchmark Solutions 101 Park Avenue - 7th Floor New York, NY 10178 Tel +1.212.220.4739 | Mobile +1.646.267.4324 www.benchmarksolutions.com<http://www.benchmarksolutions.com> <image001.png> <image001.png> Nick West Benchmark Solutions 101 Park Avenue - 7th Floor New York, NY 10178 Tel +1.212.220.4739 | Mobile +1.646.267.4324 www.benchmarksolutions.com<http://www.benchmarksolutions.com> Nick West Benchmark Solutions 101 Park Avenue - 7th Floor New York, NY 10178 Tel +1.212.220.4739 | Mobile +1.646.267.4324 www.benchmarksolutions.com <http://www.benchmarksolutions.com/> [cid:image001.png@01CCA50E.43B4A860]
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