Hi Olga, it’s indeed an error in Flink’s Summarization algorithm. The problem is the following: The vertex group value of the VertexGroupItem is null in the VertexGroupReducer. This works in the SummarizationIT case because the vertex value is of type String and the StringSerializer can deal with null values.
However, in your case where you use longs, it fails, because the LongSerializer cannot handle null values. You can verify this behaviour by changing the vertex value type to String. Then everything should work without a problem. I’ve cc’ed Martin who can tell you probably more about the Summarization algorithm. I’ve also opened a JIRA ticket [1] to fix this problem. Thanks for reporting this bug. [1] https://issues.apache.org/jira/browse/FLINK-4624 Cheers, Till On Thu, Sep 15, 2016 at 5:05 PM, Olga Golovneva <melcha...@gmail.com> wrote: > Hi Till, > > I've created a simple (Java) example to show you what's going on. The code > is in attachment and shown below. This example creates simple graph with > Double EV and Long VV. Then it runs Summarization, that should compute a > condensed version of the input graph by grouping vertices and edges based > on their values. I run this code with IntelliJ IDEA. The code executes fine > until you want to see what is written in resulted edges (just uncomment > line 46, edgesOut.print();). Then it throws the following Exception: > > _________EXCEPTION START_____________ > Exception in thread "main" > 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:830) > at org.apache.flink.runtime.jobmanager.JobManager$$ > anonfun$handleMessage$1$$anonfun$applyOrElse$8.apply(JobManager.scala:773) > at org.apache.flink.runtime.jobmanager.JobManager$$ > anonfun$handleMessage$1$$anonfun$applyOrElse$8.apply(JobManager.scala:773) > at scala.concurrent.impl.Future$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$WorkQueue. > runTask(ForkJoinPool.java:1346) > at scala.concurrent.forkjoin.ForkJoinPool.runWorker( > ForkJoinPool.java:1979) > at scala.concurrent.forkjoin.ForkJoinWorkerThread.run( > ForkJoinWorkerThread.java:107) > Caused by: org.apache.flink.types.NullFieldException: Field 2 is null, > but expected to hold a value. > at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.serialize( > TupleSerializer.java:126) > at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.serialize( > TupleSerializer.java:30) > at org.apache.flink.runtime.plugable.SerializationDelegate.write( > SerializationDelegate.java:56) > at org.apache.flink.runtime.io.network.api.serialization. > SpanningRecordSerializer.addRecord(SpanningRecordSerializer.java:83) > at org.apache.flink.runtime.io.network.api.writer.RecordWriter.emit( > RecordWriter.java:85) > at org.apache.flink.runtime.operators.shipping.OutputCollector.collect( > OutputCollector.java:65) > at org.apache.flink.runtime.operators.util.metrics. > CountingCollector.collect(CountingCollector.java:35) > at org.apache.flink.api.java.operators.translation.PlanFilterOperator$ > FlatMapFilter.flatMap(PlanFilterOperator.java:51) > at org.apache.flink.runtime.operators.chaining. > ChainedFlatMapDriver.collect(ChainedFlatMapDriver.java:80) > at org.apache.flink.runtime.operators.util.metrics. > CountingCollector.collect(CountingCollector.java:35) > at org.apache.flink.graph.library.Summarization$VertexGroupReducer.reduce( > Summarization.java:323) > at org.apache.flink.runtime.operators.GroupReduceDriver. > run(GroupReduceDriver.java:131) > at org.apache.flink.runtime.operators.BatchTask.run(BatchTask.java:486) > at org.apache.flink.runtime.operators.BatchTask.invoke(BatchTask.java:351) > at org.apache.flink.runtime.taskmanager.Task.run(Task.java:590) > at java.lang.Thread.run(Thread.java:745) > Caused by: java.lang.NullPointerException > at org.apache.flink.api.common.typeutils.base.LongSerializer. > serialize(LongSerializer.java:64) > at org.apache.flink.api.common.typeutils.base.LongSerializer. > serialize(LongSerializer.java:27) > at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.serialize( > TupleSerializer.java:124) > ... 15 more > > _____________EXCEPTION END__________________ > > It looks like the problem is in the following lines in Summarization: > > DataSet<Edge<K, EV>> edgesForGrouping = input.getEdges() > .join(vertexToRepresentativeMap) > .where(0) // source vertex id > .equalTo(0) // vertex id > .with(new SourceVertexJoinFunction<K, EV>()) > .join(vertexToRepresentativeMap) > .where(1) // target vertex id > .equalTo(0) // vertex id > .with(new TargetVertexJoinFunction<K, EV>()); > > > If you try to print edges before this step, it works fine. But after this > step my IDE gives the same exception. > > I would really appreciate any help. > > Thank you, > Olga > > _________EXAMPLE START_____________________ > > package org.apache.flink.graph.examples; > > import org.apache.flink.api.common.ProgramDescription; > import org.apache.flink.api.java.DataSet; > import org.apache.flink.api.java.ExecutionEnvironment; > import org.apache.flink.graph.Edge; > import org.apache.flink.graph.Graph; > import org.apache.flink.graph.Vertex; > import org.apache.flink.graph.library.Summarization; > import java.util.LinkedList; > import java.util.List; > > public class MySummarizationExample implements ProgramDescription { > > @SuppressWarnings("serial") > public static void main(String [] args) throws Exception { > > ExecutionEnvironment env = > ExecutionEnvironment.getExecutionEnvironment(); > > //Create graph > DataSet<Edge<Long, Double>> edges = getEdgeDataSet(env); > DataSet<Vertex<Long, Long>> vertices = getVertexDataSet(env); > Graph<Long, Long, Double> graph = Graph.fromDataSet(vertices, edges, > env); > > //emit input > System.out.println("Executing example with following > inputs:\n"+"Vertices:\n"); > vertices.print(); > System.out.println("Edges:\n"); > edges.print(); > > Graph<Long, Summarization.VertexValue<Long>, > Summarization.EdgeValue<Double>> result = graph > .run(new Summarization<Long, Long, Double>()); > > //now we want to read the output > DataSet<Edge<Long, Summarization.EdgeValue<Double>>> edgesOut = > result.getEdges(); > DataSet<Vertex<Long, Summarization.VertexValue<Long>>> verticesOut = > result.getVertices(); > > // emit result > System.out.println("Summarized graph:\n"+"Vertices:\n"); > verticesOut.print(); > System.out.println("Edges:\n"); > edgesOut.print(); > } > > @Override > public String getDescription() { > return "Summarization Example"; > } > > //Define edges > private static DataSet<Edge<Long, Double>> > getEdgeDataSet(ExecutionEnvironment env) { > Object[][] DEFAULT_EDGES = new Object[][] { > new Object[]{1L, 2L, 1.0}, > new Object[]{1L, 4L, 3.0}, > new Object[]{2L, 3L, 6.0}, > new Object[]{2L, 4L, 5.0}, > new Object[]{2L, 5L, 1.0}, > new Object[]{3L, 5L, 5.0}, > new Object[]{3L, 6L, 2.0}, > new Object[]{4L, 5L, 1.0}, > new Object[]{5L, 6L, 4.0} > }; > List<Edge<Long, Double>> edgeList = new LinkedList<Edge<Long, > Double>>(); > for (Object[] edge : DEFAULT_EDGES) { > edgeList.add(new Edge<Long, Double>((Long) edge[0], (Long) > edge[1], (Double) edge[2])); > } > return env.fromCollection(edgeList); > } > //Define vertices > private static DataSet<Vertex<Long, Long>> > getVertexDataSet(ExecutionEnvironment env) { > //We will summarize by <VV> = Long > Object[][] DEFAULT_VERTICES = new Object[][] { > new Object[]{1L, 1L}, > new Object[]{2L, 1L}, > new Object[]{3L, 5L}, > new Object[]{4L, 5L}, > new Object[]{5L, 5L} > }; > List<Vertex<Long, Long>> vertexList = new LinkedList<Vertex<Long, > Long>>(); > for (Object[] vertex : DEFAULT_VERTICES) { > vertexList.add(new Vertex<Long, Long>((Long) vertex[0], (Long) > vertex[1])); > } > return env.fromCollection(vertexList); > } > } > > _________EXAMPLE END_____________________ > > > Best regards, > Olga Golovneva > > On Thu, Sep 15, 2016 at 9:16 AM, Till Rohrmann <trohrm...@apache.org> > wrote: > >> Hi Olga, >> >> can you provide us with a little bit more details about the problem. The >> full stack trace of the exception and the program you're trying to run >> would be helpful. >> >> Cheers, >> Till >> >> On Wed, Sep 14, 2016 at 9:49 PM, Olga Golovneva <melcha...@gmail.com> >> wrote: >> >> > Hi devs, >> > >> > Do you know if there is an example (besides ITCase) of usage of >> > Summarization Library in Gelly? I'm having some problems trying to use >> it >> > in my code. Particularly, I cannot print output edges ( it throws the >> > following exception: Exception in thread "main" >> > org.apache.flink.runtime.client.JobExecutionException: Job execution >> > failed.), while vertices are printed correctly. >> > >> > Best regards, >> > Olga >> > >> > >
