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https://issues.apache.org/jira/browse/FLINK-5506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16274340#comment-16274340
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Vasia Kalavri commented on FLINK-5506:
--------------------------------------
I only had a quick look at the code; I will need to re-read the paper to make
sure the algorithm semantics are correct with the following:
I believe the problem is line 147 in {{CommunityDetection.java}}. The code
assumes we have received only positive scores, while negative ones are indeed
possible. Changing this line to {{double maxScore = -Double.MAX_VALUE;}} should
fix it.
> Java 8 - CommunityDetection.java:158 - java.lang.NullPointerException
> ---------------------------------------------------------------------
>
> Key: FLINK-5506
> URL: https://issues.apache.org/jira/browse/FLINK-5506
> Project: Flink
> Issue Type: Bug
> Components: Gelly
> Affects Versions: 1.1.4, 1.3.2, 1.4.1
> Reporter: Miguel E. Coimbra
> Labels: easyfix, newbie
> Original Estimate: 2h
> Remaining Estimate: 2h
>
> Reporting this here as per Vasia's advice.
> I am having the following problem while trying out the
> org.apache.flink.graph.library.CommunityDetection algorithm of the Gelly API
> (Java).
> Specs: JDK 1.8.0_102 x64
> Apache Flink: 1.1.4
> Suppose I have a very small (I tried an example with 38 vertices as well)
> dataset stored in a tab-separated file 3-vertex.tsv:
> {code}
> #id1 id2 score
> 0 1 0
> 0 2 0
> 0 3 0
> {code}
> This is just a central vertex with 3 neighbors (disconnected between
> themselves).
> I am loading the dataset and executing the algorithm with the following code:
> {code}
> // Load the data from the .tsv file.
> final DataSet<Tuple3<Long, Long, Double>> edgeTuples =
> env.readCsvFile(inputPath)
> .fieldDelimiter("\t") // node IDs are separated by spaces
> .ignoreComments("#") // comments start with "%"
> .types(Long.class, Long.class, Double.class);
> // Generate a graph and add reverse edges (undirected).
> final Graph<Long, Long, Double> graph = Graph.fromTupleDataSet(edgeTuples,
> new MapFunction<Long, Long>() {
> private static final long serialVersionUID = 8713516577419451509L;
> public Long map(Long value) {
> return value;
> }
> },
> env).getUndirected();
> // CommunityDetection parameters.
> final double hopAttenuationDelta = 0.5d;
> final int iterationCount = 10;
> // Prepare and trigger the execution.
> DataSet<Vertex<Long, Long>> vs = graph.run(new
> org.apache.flink.graph.library.CommunityDetection<Long>(iterationCount,
> hopAttenuationDelta)).getVertices();
> vs.print();
> {code}
> Running this code throws the following exception (check the bold line):
> {code}
> org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$8.apply$mcV$sp(JobManager.scala:805)
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$8.apply(JobManager.scala:751)
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$8.apply(JobManager.scala:751)
> at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
> at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
> at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:41)
> at
> akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:401)
> at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
> at
> scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.pollAndExecAll(ForkJoinPool.java:1253)
> at
> scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1346)
> at
> scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
> at
> scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
> Caused by: java.lang.NullPointerException
> at
> org.apache.flink.graph.library.CommunityDetection$VertexLabelUpdater.updateVertex(CommunityDetection.java:158)
> at
> org.apache.flink.graph.spargel.ScatterGatherIteration$GatherUdfSimpleVV.coGroup(ScatterGatherIteration.java:389)
> at
> org.apache.flink.runtime.operators.CoGroupWithSolutionSetSecondDriver.run(CoGroupWithSolutionSetSecondDriver.java:218)
> at org.apache.flink.runtime.operators.BatchTask.run(BatchTask.java:486)
> at
> org.apache.flink.runtime.iterative.task.AbstractIterativeTask.run(AbstractIterativeTask.java:146)
> at
> org.apache.flink.runtime.iterative.task.IterationTailTask.run(IterationTailTask.java:107)
> at org.apache.flink.runtime.operators.BatchTask.invoke(BatchTask.java:351)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:642)
> at java.lang.Thread.run(Thread.java:745)
> {code}
> After a further look, I set a breakpoint (Eclipse IDE debugging) at the line
> in bold:
> org.apache.flink.graph.library.CommunityDetection.java (source code accessed
> automatically by Maven)
> // find the highest score of maxScoreLabel
> double highestScore = labelsWithHighestScore.get(maxScoreLabel);
> - maxScoreLabel has the value 3.
> - labelsWithHighestScore was initialized as: Map<Long, Double>
> labelsWithHighestScore = new TreeMap<>();
> - labelsWithHighestScore is a TreeMap<Long, Double> and has the values:
> {0=0.0}
> null
> null
> [0=0.0]
> null
> 1
> It seems that the value 3 should have been added to that
> labelsWithHighestScore some time during execution, but because it wasn't, an
> exception is thrown.
> In the mailing list, Vasia speculates that the problem is that the
> implementation assumes that labelsWithHighestScores contains the vertex
> itself as initial label.
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