Hi everyone, I have a driver holding a reference to an RDD. The driver would like to "visit" each item in the RDD in order, say with a visitor object that invokes visit(item) to modify that visitor's internal state. The visiting is not commutative (e.g. Visiting item A then B makes a different internal state from visiting item B then item A). Items in the RDD also are not necessarily distinct.
I've looked into accumulators which don't work because they require the operation to be commutative. Collect() will not work because the RDD is too large; in general, bringing the whole RDD into one partition won't work since the RDD is too large. Is it possible to iterate over the items in an RDD in order without bringing the entire dataset into a single JVM at a time, and/or obtain chunks of the RDD in order on the driver? We've tried using the internal iterator() method. In some cases, we get a stack trace (running locally with 3 threads). I've included the stack trace below. Thanks, -Matt Cheah org.apache.spark.SparkException: Error communicating with MapOutputTracker at org.apache.spark.MapOutputTracker.askTracker(MapOutputTracker.scala:84) at org.apache.spark.MapOutputTracker.getServerStatuses(MapOutputTracker.scala:170) at org.apache.spark.BlockStoreShuffleFetcher.fetch(BlockStoreShuffleFetcher.scala:39) at org.apache.spark.rdd.ShuffledRDD.compute(ShuffledRDD.scala:59) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:237) at org.apache.spark.rdd.RDD.iterator(RDD.scala:226) at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:36) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:237) at org.apache.spark.rdd.RDD.iterator(RDD.scala:226) at org.apache.spark.rdd.MappedRDD.compute(MappedRDD.scala:29) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:237) at org.apache.spark.rdd.RDD.iterator(RDD.scala:226) at org.apache.spark.api.java.JavaRDDLike$class.iterator(JavaRDDLike.scala:60) at org.apache.spark.api.java.JavaRDD.iterator(JavaRDD.scala:25) at com.palantir.finance.server.service.datatable.SparkRawDataTableProvider.compute(SparkRawDataTableProvider.java:76) at com.palantir.finance.server.datatable.spark.SparkDataTable.visit(SparkDataTable.java:83) at com.palantir.finance.server.datatable.DataTableImplementationParityTests.runDataTableTest(DataTableImplementationParityTests.java:129) at com.palantir.finance.server.datatable.DataTableImplementationParityTests.testParityOnSort(DataTableImplementationParityTests.java:102) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:48) at org.junit.rules.RunRules.evaluate(RunRules.java:20) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:48) at com.palantir.finance.commons.service.ServiceThreadContainerRule$1.evaluate(ServiceThreadContainerRule.java:28) at org.junit.rules.RunRules.evaluate(RunRules.java:20) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) Caused by: java.util.concurrent.TimeoutException: Futures timed out after [10000] milliseconds at org.apache.spark.internal.akka.dispatch.DefaultPromise.ready(Future.scala:870) at org.apache.spark.internal.akka.dispatch.DefaultPromise.result(Future.scala:874) at org.apache.spark.internal.akka.dispatch.Await$.result(Future.scala:74) at org.apache.spark.MapOutputTracker.askTracker(MapOutputTracker.scala:81) ... 46 more
