Examples with CompilerException org.apache.flink.optimizer.CompilerException used on opensource projects

Example 6 with CompilerException

use of org.apache.flink.optimizer.CompilerException in project flink by apache.

the class TwoInputNode method setInput.

@Override
public void setInput(Map<Operator<?>, OptimizerNode> contractToNode, ExecutionMode defaultExecutionMode) {
    // see if there is a hint that dictates which shipping strategy to use for BOTH inputs
    final Configuration conf = getOperator().getParameters();
    ShipStrategyType preSet1 = null;
    ShipStrategyType preSet2 = null;
    String shipStrategy = conf.getString(Optimizer.HINT_SHIP_STRATEGY, null);
    if (shipStrategy != null) {
        if (Optimizer.HINT_SHIP_STRATEGY_FORWARD.equals(shipStrategy)) {
            preSet1 = preSet2 = ShipStrategyType.FORWARD;
        } else if (Optimizer.HINT_SHIP_STRATEGY_BROADCAST.equals(shipStrategy)) {
            preSet1 = preSet2 = ShipStrategyType.BROADCAST;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_HASH.equals(shipStrategy)) {
            preSet1 = preSet2 = ShipStrategyType.PARTITION_HASH;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_RANGE.equals(shipStrategy)) {
            preSet1 = preSet2 = ShipStrategyType.PARTITION_RANGE;
        } else if (shipStrategy.equalsIgnoreCase(Optimizer.HINT_SHIP_STRATEGY_REPARTITION)) {
            preSet1 = preSet2 = ShipStrategyType.PARTITION_RANDOM;
        } else {
            throw new CompilerException("Unknown hint for shipping strategy: " + shipStrategy);
        }
    }
    // see if there is a hint that dictates which shipping strategy to use for the FIRST input
    shipStrategy = conf.getString(Optimizer.HINT_SHIP_STRATEGY_FIRST_INPUT, null);
    if (shipStrategy != null) {
        if (Optimizer.HINT_SHIP_STRATEGY_FORWARD.equals(shipStrategy)) {
            preSet1 = ShipStrategyType.FORWARD;
        } else if (Optimizer.HINT_SHIP_STRATEGY_BROADCAST.equals(shipStrategy)) {
            preSet1 = ShipStrategyType.BROADCAST;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_HASH.equals(shipStrategy)) {
            preSet1 = ShipStrategyType.PARTITION_HASH;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_RANGE.equals(shipStrategy)) {
            preSet1 = ShipStrategyType.PARTITION_RANGE;
        } else if (shipStrategy.equalsIgnoreCase(Optimizer.HINT_SHIP_STRATEGY_REPARTITION)) {
            preSet1 = ShipStrategyType.PARTITION_RANDOM;
        } else {
            throw new CompilerException("Unknown hint for shipping strategy of input one: " + shipStrategy);
        }
    }
    // see if there is a hint that dictates which shipping strategy to use for the SECOND input
    shipStrategy = conf.getString(Optimizer.HINT_SHIP_STRATEGY_SECOND_INPUT, null);
    if (shipStrategy != null) {
        if (Optimizer.HINT_SHIP_STRATEGY_FORWARD.equals(shipStrategy)) {
            preSet2 = ShipStrategyType.FORWARD;
        } else if (Optimizer.HINT_SHIP_STRATEGY_BROADCAST.equals(shipStrategy)) {
            preSet2 = ShipStrategyType.BROADCAST;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_HASH.equals(shipStrategy)) {
            preSet2 = ShipStrategyType.PARTITION_HASH;
        } else if (Optimizer.HINT_SHIP_STRATEGY_REPARTITION_RANGE.equals(shipStrategy)) {
            preSet2 = ShipStrategyType.PARTITION_RANGE;
        } else if (shipStrategy.equalsIgnoreCase(Optimizer.HINT_SHIP_STRATEGY_REPARTITION)) {
            preSet2 = ShipStrategyType.PARTITION_RANDOM;
        } else {
            throw new CompilerException("Unknown hint for shipping strategy of input two: " + shipStrategy);
        }
    }
    // get the predecessors
    DualInputOperator<?, ?, ?, ?> contr = getOperator();
    Operator<?> leftPred = contr.getFirstInput();
    Operator<?> rightPred = contr.getSecondInput();
    OptimizerNode pred1;
    DagConnection conn1;
    if (leftPred == null) {
        throw new CompilerException("Error: Node for '" + getOperator().getName() + "' has no input set for first input.");
    } else {
        pred1 = contractToNode.get(leftPred);
        conn1 = new DagConnection(pred1, this, defaultExecutionMode);
        if (preSet1 != null) {
            conn1.setShipStrategy(preSet1);
        }
    }
    // create the connection and add it
    this.input1 = conn1;
    pred1.addOutgoingConnection(conn1);
    OptimizerNode pred2;
    DagConnection conn2;
    if (rightPred == null) {
        throw new CompilerException("Error: Node for '" + getOperator().getName() + "' has no input set for second input.");
    } else {
        pred2 = contractToNode.get(rightPred);
        conn2 = new DagConnection(pred2, this, defaultExecutionMode);
        if (preSet2 != null) {
            conn2.setShipStrategy(preSet2);
        }
    }
    // create the connection and add it
    this.input2 = conn2;
    pred2.addOutgoingConnection(conn2);
}

Example 7 with CompilerException

use of org.apache.flink.optimizer.CompilerException in project flink by apache.

the class JobGraphGenerator method compileJobGraph.

public JobGraph compileJobGraph(OptimizedPlan program, JobID jobId) {
    if (program == null) {
        throw new NullPointerException("Program is null, did you called " + "ExecutionEnvironment.execute()");
    }
    if (jobId == null) {
        jobId = JobID.generate();
    }
    this.vertices = new HashMap<PlanNode, JobVertex>();
    this.chainedTasks = new HashMap<PlanNode, TaskInChain>();
    this.chainedTasksInSequence = new ArrayList<TaskInChain>();
    this.auxVertices = new ArrayList<JobVertex>();
    this.iterations = new HashMap<IterationPlanNode, IterationDescriptor>();
    this.iterationStack = new ArrayList<IterationPlanNode>();
    this.sharingGroup = new SlotSharingGroup();
    // this starts the traversal that generates the job graph
    program.accept(this);
    // sanity check that we are not somehow in an iteration at the end
    if (this.currentIteration != null) {
        throw new CompilerException("The graph translation ended prematurely, leaving an unclosed iteration.");
    }
    // finalize the iterations
    for (IterationDescriptor iteration : this.iterations.values()) {
        if (iteration.getIterationNode() instanceof BulkIterationPlanNode) {
            finalizeBulkIteration(iteration);
        } else if (iteration.getIterationNode() instanceof WorksetIterationPlanNode) {
            finalizeWorksetIteration(iteration);
        } else {
            throw new CompilerException();
        }
    }
    // parents' configurations
    for (TaskInChain tic : this.chainedTasksInSequence) {
        TaskConfig t = new TaskConfig(tic.getContainingVertex().getConfiguration());
        t.addChainedTask(tic.getChainedTask(), tic.getTaskConfig(), tic.getTaskName());
    }
    // ----- attach the additional info to the job vertices, for display in the runtime monitor
    attachOperatorNamesAndDescriptions();
    // ----------- finalize the job graph -----------
    // create the job graph object
    JobGraph graph = new JobGraph(jobId, program.getJobName());
    try {
        graph.setExecutionConfig(program.getOriginalPlan().getExecutionConfig());
    } catch (IOException e) {
        throw new CompilerException("Could not serialize the ExecutionConfig." + "This indicates that non-serializable types (like custom serializers) were registered");
    }
    graph.setAllowQueuedScheduling(false);
    graph.setSessionTimeout(program.getOriginalPlan().getSessionTimeout());
    // add vertices to the graph
    for (JobVertex vertex : this.vertices.values()) {
        graph.addVertex(vertex);
    }
    for (JobVertex vertex : this.auxVertices) {
        graph.addVertex(vertex);
        vertex.setSlotSharingGroup(sharingGroup);
    }
    // add registered cache file into job configuration
    for (Entry<String, DistributedCacheEntry> e : program.getOriginalPlan().getCachedFiles()) {
        DistributedCache.writeFileInfoToConfig(e.getKey(), e.getValue(), graph.getJobConfiguration());
    }
    // release all references again
    this.vertices = null;
    this.chainedTasks = null;
    this.chainedTasksInSequence = null;
    this.auxVertices = null;
    this.iterations = null;
    this.iterationStack = null;
    // return job graph
    return graph;
}

Example 8 with CompilerException

use of org.apache.flink.optimizer.CompilerException in project flink by apache.

the class JobGraphGenerator method finalizeWorksetIteration.

private void finalizeWorksetIteration(IterationDescriptor descr) {
    final WorksetIterationPlanNode iterNode = (WorksetIterationPlanNode) descr.getIterationNode();
    final JobVertex headVertex = descr.getHeadTask();
    final TaskConfig headConfig = new TaskConfig(headVertex.getConfiguration());
    final TaskConfig headFinalOutputConfig = descr.getHeadFinalResultConfig();
    // ------------ finalize the head config with the final outputs and the sync gate ------------
    {
        final int numStepFunctionOuts = headConfig.getNumOutputs();
        final int numFinalOuts = headFinalOutputConfig.getNumOutputs();
        if (numStepFunctionOuts == 0) {
            throw new CompilerException("The workset iteration has no operation on the workset inside the step function.");
        }
        headConfig.setIterationHeadFinalOutputConfig(headFinalOutputConfig);
        headConfig.setIterationHeadIndexOfSyncOutput(numStepFunctionOuts + numFinalOuts);
        final double relativeMemory = iterNode.getRelativeMemoryPerSubTask();
        if (relativeMemory <= 0) {
            throw new CompilerException("Bug: No memory has been assigned to the workset iteration.");
        }
        headConfig.setIsWorksetIteration();
        headConfig.setRelativeBackChannelMemory(relativeMemory / 2);
        headConfig.setRelativeSolutionSetMemory(relativeMemory / 2);
        // set the solution set serializer and comparator
        headConfig.setSolutionSetSerializer(iterNode.getSolutionSetSerializer());
        headConfig.setSolutionSetComparator(iterNode.getSolutionSetComparator());
    }
    // --------------------------- create the sync task ---------------------------
    final TaskConfig syncConfig;
    {
        final JobVertex sync = new JobVertex("Sync (" + iterNode.getNodeName() + ")");
        sync.setResources(iterNode.getMinResources(), iterNode.getPreferredResources());
        sync.setInvokableClass(IterationSynchronizationSinkTask.class);
        sync.setParallelism(1);
        sync.setMaxParallelism(1);
        this.auxVertices.add(sync);
        syncConfig = new TaskConfig(sync.getConfiguration());
        syncConfig.setGateIterativeWithNumberOfEventsUntilInterrupt(0, headVertex.getParallelism());
        // set the number of iteration / convergence criterion for the sync
        final int maxNumIterations = iterNode.getIterationNode().getIterationContract().getMaximumNumberOfIterations();
        if (maxNumIterations < 1) {
            throw new CompilerException("Cannot create workset iteration with unspecified maximum number of iterations.");
        }
        syncConfig.setNumberOfIterations(maxNumIterations);
        // connect the sync task
        sync.connectNewDataSetAsInput(headVertex, DistributionPattern.POINTWISE, ResultPartitionType.PIPELINED);
    }
    // ----------------------------- create the iteration tails -----------------------------
    // ----------------------- for next workset and solution set delta-----------------------
    {
        // we have three possible cases:
        // 1) Two tails, one for workset update, one for solution set update
        // 2) One tail for workset update, solution set update happens in an intermediate task
        // 3) One tail for solution set update, workset update happens in an intermediate task
        final PlanNode nextWorksetNode = iterNode.getNextWorkSetPlanNode();
        final PlanNode solutionDeltaNode = iterNode.getSolutionSetDeltaPlanNode();
        final boolean hasWorksetTail = nextWorksetNode.getOutgoingChannels().isEmpty();
        final boolean hasSolutionSetTail = (!iterNode.isImmediateSolutionSetUpdate()) || (!hasWorksetTail);
        {
            // get the vertex for the workset update
            final TaskConfig worksetTailConfig;
            JobVertex nextWorksetVertex = this.vertices.get(nextWorksetNode);
            if (nextWorksetVertex == null) {
                // nextWorksetVertex is chained
                TaskInChain taskInChain = this.chainedTasks.get(nextWorksetNode);
                if (taskInChain == null) {
                    throw new CompilerException("Bug: Next workset node not found as vertex or chained task.");
                }
                nextWorksetVertex = taskInChain.getContainingVertex();
                worksetTailConfig = taskInChain.getTaskConfig();
            } else {
                worksetTailConfig = new TaskConfig(nextWorksetVertex.getConfiguration());
            }
            // mark the node to perform workset updates
            worksetTailConfig.setIsWorksetIteration();
            worksetTailConfig.setIsWorksetUpdate();
            if (hasWorksetTail) {
                nextWorksetVertex.setInvokableClass(IterationTailTask.class);
                worksetTailConfig.setOutputSerializer(iterNode.getWorksetSerializer());
            }
        }
        {
            final TaskConfig solutionDeltaConfig;
            JobVertex solutionDeltaVertex = this.vertices.get(solutionDeltaNode);
            if (solutionDeltaVertex == null) {
                // last op is chained
                TaskInChain taskInChain = this.chainedTasks.get(solutionDeltaNode);
                if (taskInChain == null) {
                    throw new CompilerException("Bug: Solution Set Delta not found as vertex or chained task.");
                }
                solutionDeltaVertex = taskInChain.getContainingVertex();
                solutionDeltaConfig = taskInChain.getTaskConfig();
            } else {
                solutionDeltaConfig = new TaskConfig(solutionDeltaVertex.getConfiguration());
            }
            solutionDeltaConfig.setIsWorksetIteration();
            solutionDeltaConfig.setIsSolutionSetUpdate();
            if (hasSolutionSetTail) {
                solutionDeltaVertex.setInvokableClass(IterationTailTask.class);
                solutionDeltaConfig.setOutputSerializer(iterNode.getSolutionSetSerializer());
                // tell the head that it needs to wait for the solution set updates
                headConfig.setWaitForSolutionSetUpdate();
            } else {
                // no tail, intermediate update. must be immediate update
                if (!iterNode.isImmediateSolutionSetUpdate()) {
                    throw new CompilerException("A solution set update without dedicated tail is not set to perform immediate updates.");
                }
                solutionDeltaConfig.setIsSolutionSetUpdateWithoutReprobe();
            }
        }
    }
    // ------------------- register the aggregators -------------------
    AggregatorRegistry aggs = iterNode.getIterationNode().getIterationContract().getAggregators();
    Collection<AggregatorWithName<?>> allAggregators = aggs.getAllRegisteredAggregators();
    for (AggregatorWithName<?> agg : allAggregators) {
        if (agg.getName().equals(WorksetEmptyConvergenceCriterion.AGGREGATOR_NAME)) {
            throw new CompilerException("User defined aggregator used the same name as built-in workset " + "termination check aggregator: " + WorksetEmptyConvergenceCriterion.AGGREGATOR_NAME);
        }
    }
    headConfig.addIterationAggregators(allAggregators);
    syncConfig.addIterationAggregators(allAggregators);
    String convAggName = aggs.getConvergenceCriterionAggregatorName();
    ConvergenceCriterion<?> convCriterion = aggs.getConvergenceCriterion();
    if (convCriterion != null || convAggName != null) {
        if (convCriterion == null) {
            throw new CompilerException("Error: Convergence criterion aggregator set, but criterion is null.");
        }
        if (convAggName == null) {
            throw new CompilerException("Error: Aggregator convergence criterion set, but aggregator is null.");
        }
        syncConfig.setConvergenceCriterion(convAggName, convCriterion);
    }
    headConfig.addIterationAggregator(WorksetEmptyConvergenceCriterion.AGGREGATOR_NAME, new LongSumAggregator());
    syncConfig.addIterationAggregator(WorksetEmptyConvergenceCriterion.AGGREGATOR_NAME, new LongSumAggregator());
    syncConfig.setImplicitConvergenceCriterion(WorksetEmptyConvergenceCriterion.AGGREGATOR_NAME, new WorksetEmptyConvergenceCriterion());
}

Example 9 with CompilerException

use of org.apache.flink.optimizer.CompilerException in project flink by apache.

the class JobGraphGenerator method translateChannel.

private int translateChannel(Channel input, int inputIndex, JobVertex targetVertex, TaskConfig targetVertexConfig, boolean isBroadcast) throws Exception {
    final PlanNode inputPlanNode = input.getSource();
    final Iterator<Channel> allInChannels;
    if (inputPlanNode instanceof NAryUnionPlanNode) {
        allInChannels = ((NAryUnionPlanNode) inputPlanNode).getListOfInputs().iterator();
        // deadlocks when closing a branching flow at runtime.
        for (Channel in : inputPlanNode.getInputs()) {
            if (input.getDataExchangeMode().equals(DataExchangeMode.BATCH)) {
                in.setDataExchangeMode(DataExchangeMode.BATCH);
            }
            if (isBroadcast) {
                in.setShipStrategy(ShipStrategyType.BROADCAST, in.getDataExchangeMode());
            }
        }
    } else if (inputPlanNode instanceof BulkPartialSolutionPlanNode) {
        if (this.vertices.get(inputPlanNode) == null) {
            // merged iteration head
            final BulkPartialSolutionPlanNode pspn = (BulkPartialSolutionPlanNode) inputPlanNode;
            final BulkIterationPlanNode iterationNode = pspn.getContainingIterationNode();
            // check if the iteration's input is a union
            if (iterationNode.getInput().getSource() instanceof NAryUnionPlanNode) {
                allInChannels = (iterationNode.getInput().getSource()).getInputs().iterator();
            } else {
                allInChannels = Collections.singletonList(iterationNode.getInput()).iterator();
            }
            // also, set the index of the gate with the partial solution
            targetVertexConfig.setIterationHeadPartialSolutionOrWorksetInputIndex(inputIndex);
        } else {
            // standalone iteration head
            allInChannels = Collections.singletonList(input).iterator();
        }
    } else if (inputPlanNode instanceof WorksetPlanNode) {
        if (this.vertices.get(inputPlanNode) == null) {
            // merged iteration head
            final WorksetPlanNode wspn = (WorksetPlanNode) inputPlanNode;
            final WorksetIterationPlanNode iterationNode = wspn.getContainingIterationNode();
            // check if the iteration's input is a union
            if (iterationNode.getInput2().getSource() instanceof NAryUnionPlanNode) {
                allInChannels = (iterationNode.getInput2().getSource()).getInputs().iterator();
            } else {
                allInChannels = Collections.singletonList(iterationNode.getInput2()).iterator();
            }
            // also, set the index of the gate with the partial solution
            targetVertexConfig.setIterationHeadPartialSolutionOrWorksetInputIndex(inputIndex);
        } else {
            // standalone iteration head
            allInChannels = Collections.singletonList(input).iterator();
        }
    } else if (inputPlanNode instanceof SolutionSetPlanNode) {
        // rather than a vertex connection
        return 0;
    } else {
        allInChannels = Collections.singletonList(input).iterator();
    }
    // check that the type serializer is consistent
    TypeSerializerFactory<?> typeSerFact = null;
    // accounting for channels on the dynamic path
    int numChannelsTotal = 0;
    int numChannelsDynamicPath = 0;
    int numDynamicSenderTasksTotal = 0;
    // expand the channel to all the union channels, in case there is a union operator at its source
    while (allInChannels.hasNext()) {
        final Channel inConn = allInChannels.next();
        // sanity check the common serializer
        if (typeSerFact == null) {
            typeSerFact = inConn.getSerializer();
        } else if (!typeSerFact.equals(inConn.getSerializer())) {
            throw new CompilerException("Conflicting types in union operator.");
        }
        final PlanNode sourceNode = inConn.getSource();
        JobVertex sourceVertex = this.vertices.get(sourceNode);
        TaskConfig sourceVertexConfig;
        if (sourceVertex == null) {
            // this predecessor is chained to another task or an iteration
            final TaskInChain chainedTask;
            final IterationDescriptor iteration;
            if ((chainedTask = this.chainedTasks.get(sourceNode)) != null) {
                // push chained task
                if (chainedTask.getContainingVertex() == null) {
                    throw new IllegalStateException("Bug: Chained task has not been assigned its containing vertex when connecting.");
                }
                sourceVertex = chainedTask.getContainingVertex();
                sourceVertexConfig = chainedTask.getTaskConfig();
            } else if ((iteration = this.iterations.get(sourceNode)) != null) {
                // predecessor is an iteration
                sourceVertex = iteration.getHeadTask();
                sourceVertexConfig = iteration.getHeadFinalResultConfig();
            } else {
                throw new CompilerException("Bug: Could not resolve source node for a channel.");
            }
        } else {
            // predecessor is its own vertex
            sourceVertexConfig = new TaskConfig(sourceVertex.getConfiguration());
        }
        DistributionPattern pattern = connectJobVertices(inConn, inputIndex, sourceVertex, sourceVertexConfig, targetVertex, targetVertexConfig, isBroadcast);
        // accounting on channels and senders
        numChannelsTotal++;
        if (inConn.isOnDynamicPath()) {
            numChannelsDynamicPath++;
            numDynamicSenderTasksTotal += getNumberOfSendersPerReceiver(pattern, sourceVertex.getParallelism(), targetVertex.getParallelism());
        }
    }
    // is a union between nodes on the static and nodes on the dynamic path
    if (numChannelsDynamicPath > 0 && numChannelsTotal != numChannelsDynamicPath) {
        throw new CompilerException("Error: It is currently not supported to union between dynamic and static path in an iteration.");
    }
    if (numDynamicSenderTasksTotal > 0) {
        if (isBroadcast) {
            targetVertexConfig.setBroadcastGateIterativeWithNumberOfEventsUntilInterrupt(inputIndex, numDynamicSenderTasksTotal);
        } else {
            targetVertexConfig.setGateIterativeWithNumberOfEventsUntilInterrupt(inputIndex, numDynamicSenderTasksTotal);
        }
    }
    // the local strategy is added only once. in non-union case that is the actual edge,
    // in the union case, it is the edge between union and the target node
    addLocalInfoFromChannelToConfig(input, targetVertexConfig, inputIndex, isBroadcast);
    return 1;
}

Example 10 with CompilerException

use of org.apache.flink.optimizer.CompilerException in project flink by apache.

the class JobGraphGenerator method createBulkIterationHead.

private JobVertex createBulkIterationHead(BulkPartialSolutionPlanNode pspn) {
    // get the bulk iteration that corresponds to this partial solution node
    final BulkIterationPlanNode iteration = pspn.getContainingIterationNode();
    // check whether we need an individual vertex for the partial solution, or whether we
    // attach ourselves to the vertex of the parent node. We can combine the head with a node of 
    // the step function, if
    // 1) There is one parent that the partial solution connects to via a forward pattern and no
    //    local strategy
    // 2) parallelism and the number of subtasks per instance does not change
    // 3) That successor is not a union
    // 4) That successor is not itself the last node of the step function
    // 5) There is no local strategy on the edge for the initial partial solution, as
    //    this translates to a local strategy that would only be executed in the first iteration
    final boolean merge;
    if (mergeIterationAuxTasks && pspn.getOutgoingChannels().size() == 1) {
        final Channel c = pspn.getOutgoingChannels().get(0);
        final PlanNode successor = c.getTarget();
        merge = c.getShipStrategy() == ShipStrategyType.FORWARD && c.getLocalStrategy() == LocalStrategy.NONE && c.getTempMode() == TempMode.NONE && successor.getParallelism() == pspn.getParallelism() && !(successor instanceof NAryUnionPlanNode) && successor != iteration.getRootOfStepFunction() && iteration.getInput().getLocalStrategy() == LocalStrategy.NONE;
    } else {
        merge = false;
    }
    // create or adopt the head vertex
    final JobVertex toReturn;
    final JobVertex headVertex;
    final TaskConfig headConfig;
    if (merge) {
        final PlanNode successor = pspn.getOutgoingChannels().get(0).getTarget();
        headVertex = this.vertices.get(successor);
        if (headVertex == null) {
            throw new CompilerException("Bug: Trying to merge solution set with its successor, but successor has not been created.");
        }
        // reset the vertex type to iteration head
        headVertex.setInvokableClass(IterationHeadTask.class);
        headConfig = new TaskConfig(headVertex.getConfiguration());
        toReturn = null;
    } else {
        // instantiate the head vertex and give it a no-op driver as the driver strategy.
        // everything else happens in the post visit, after the input (the initial partial solution)
        // is connected.
        headVertex = new JobVertex("PartialSolution (" + iteration.getNodeName() + ")");
        headVertex.setResources(iteration.getMinResources(), iteration.getPreferredResources());
        headVertex.setInvokableClass(IterationHeadTask.class);
        headConfig = new TaskConfig(headVertex.getConfiguration());
        headConfig.setDriver(NoOpDriver.class);
        toReturn = headVertex;
    }
    // create the iteration descriptor and the iteration to it
    IterationDescriptor descr = this.iterations.get(iteration);
    if (descr == null) {
        throw new CompilerException("Bug: Iteration descriptor was not created at when translating the iteration node.");
    }
    descr.setHeadTask(headVertex, headConfig);
    return toReturn;
}