Thank you Matthew. Now writing a custom vertex class and input format seems doable! Thank you.
-- Vivek ________________________________ From: Matthew Saltz <sal...@gmail.com> Sent: Monday, July 21, 2014 5:50 PM To: user@giraph.apache.org Subject: Re: Setting variable value in Compute class and using it in the next superstep Yeah, that's true. Sorry I forgot that part. Luckily, it isn't too tricky either, depending on the input format of your graph. Here's another example<https://gist.github.com/saltzm/ab7172c57dec927061be> to get you started, for a very simple input format for edges with no values. I basically took the code straight from here<http://giraph.apache.org/apidocs/org/apache/giraph/io/formats/LongLongNullTextInputFormat.html> and modified where I needed to it to return the InputFormat that I needed for my code. You'll probably be better off digging through some of the already implemented InputFormat classes that come with Giraph to do something similar, since I'm guessing your input files will be different than mine. Take a look at the subclasses of TextVertexInputFormat<http://giraph.apache.org/apidocs/org/apache/giraph/io/formats/TextVertexInputFormat.html>, since they deal with a lot of common input format styles, and see if you can modify their code to work with your custom vertex data format. Now, the example I give you is also easy because I just use the default constructor of the class, but if you need to load additional data from the file into your vertex data and the default constructor isn't appropriate, you may have to do some extra parsing and legwork for that. Best of luck, Matthew On Tue, Jul 22, 2014 at 12:28 AM, Sardeshmukh, Vivek <vivek-sardeshm...@uiowa.edu<mailto:vivek-sardeshm...@uiowa.edu>> wrote: Thank you Matthew for the example link. It is helpful. I'll give it a shot. If I have a custom vertex class isn't it necessary to change the VertexInputFormat class too? Since this class "loads" the data into the vertex and if vertex has a custom value field then it doesn't know how to load the input. Am I right? Vivek ________________________________ From: Schweiger, Tom <thschwei...@ebay.com<mailto:thschwei...@ebay.com>> Sent: Monday, July 21, 2014 5:16 PM To: user@giraph.apache.org<mailto:user@giraph.apache.org> Subject: RE: Setting variable value in Compute class and using it in the next superstep For more than one flag, a custom class is necessary (unless you're able to, say, toggle the sign bit to get double usage out or a value). I've started a private thread with Vivek to get a better understanding of what he was trying to solve. And you are also correct that there isn't much to writing a custom vertex class. The key is making sure you read and write in the same order. Likewise, extending a vertex reader can be quite simple. ________________________________ From: Matthew Saltz [sal...@gmail.com<mailto:sal...@gmail.com>] Sent: Monday, July 21, 2014 3:09 PM To: user@giraph.apache.org<mailto:user@giraph.apache.org> Subject: Re: Setting variable value in Compute class and using it in the next superstep Tom, If it's necessary to store more than one flag though, for example, won't a custom class be necessary? I'm a beginner too, so I apologize if I'm incorrect about that. Just to be clarify, to keep persistent data for a vertex from one superstep to the next, it is necessary to encapsulate it in the type used for the 'V', right? In other words, if Vivek tries to use a normal member variable for the Computation class, it won't work will it? Also, just to point out, there actually isn't too much involved with writing your own custom vertex class. Here's a quick example<https://gist.github.com/saltzm/692fba1d3aade035ce9c> to get you started. Within your compute() method you can access the data in this class by doing SampleVertexData d = vertex.getValue(); and then using d.setFlag(true) or boolean currentFlag = d.getFlag() for example. And your computation class is now something like public class MyComputation extends BasicComputation<IdType, SampleVertexData, EdgeType, MessageType> { @Override public void compute(Vertex<IdType, SampleVertexData, EdgeType> vertex, Iterable<MessageType> messages) {.....} ... } As a warning, for this class I'm using Hadoop 0.20.203 and I'm also a beginner, so take everything I say with a grain of salt, and Tom please correct me if I'm wrong. Best of luck, Matthew On Mon, Jul 21, 2014 at 11:37 PM, Schweiger, Tom <thschwei...@ebay.com<mailto:thschwei...@ebay.com>> wrote: And in answer of : This post also suggests (along with what I described above) to have a field in the vertex value itself. For that I need to change the vertex input format and also create my own custom vertex class. Is it really necessary? No, you don't need a custom vertex class or vertex input format. You can create/initialize the value at the beginning of the first superstep. ________________________________ From: Sardeshmukh, Vivek [vivek-sardeshm...@uiowa.edu<mailto:vivek-sardeshm...@uiowa.edu>] Sent: Monday, July 21, 2014 2:05 PM To: user@giraph.apache.org<mailto:user@giraph.apache.org> Subject: Setting variable value in Compute class and using it in the next superstep Hi, all-- In my algorithm, I need to set a flag if certain conditions hold (locally at a vertex v). If this flag is set then execute some other block of code *only once*, and do nothing until some other condition is hold. My question is, can I declare a flag variable in the class where I override compute function? I defined the flag as a public variable and setting it once the conditions are met but it seems the value is not "carried" over to the next superstep. I dig a little bit in this mailing list and found this https://www.mail-archive.com/user@giraph.apache.org/msg01266.html This post also suggests (along with what I described above) to have a field in the vertex value itself. For that I need to change the vertex input format and also create my own custom vertex class. Is it really necessary? By the way, I am using Giraph 1.1.0 compiled against Hadoop 1.0.3. I was able to run SimpleShortestPathComputation successfully. Here are more technical details of my algorithm: I am trying to implement Delta-stepping shortest path algorithm ( http://dl.acm.org/citation.cfm?id=740136 or http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.46.2200 ). This was mentioned in Pregel paper. A vertex "relax" light edges if it belongs to the minimum bucket index (of course, aggregators!). Once a vertex is done with relaxing light edges it relaxes heavy edges (here is where I need a flag) once. A vertex may be "re-inserted" to a newer bucket and may have to execute all the steps that I described here again. Thanks. Sincerely, Vivek A beginner in Giraph (and Java too!)
