johnyangk commented on a change in pull request #104: [NEMO-183] DAG-centric translation from Beam pipeline to IR DAG URL: https://github.com/apache/incubator-nemo/pull/104#discussion_r210500940
########## File path: compiler/frontend/beam/src/main/java/edu/snu/nemo/compiler/frontend/beam/PipelineVisitor.java ########## @@ -0,0 +1,291 @@ +/* + * Copyright (C) 2018 Seoul National University + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package edu.snu.nemo.compiler.frontend.beam; + +import edu.snu.nemo.common.dag.DAG; +import edu.snu.nemo.common.dag.DAGBuilder; +import edu.snu.nemo.common.dag.Edge; +import edu.snu.nemo.common.dag.Vertex; +import org.apache.beam.sdk.Pipeline; +import org.apache.beam.sdk.runners.TransformHierarchy; +import org.apache.beam.sdk.transforms.ParDo; +import org.apache.beam.sdk.transforms.View; +import org.apache.beam.sdk.values.PValue; + +import java.util.*; + +/** + * Traverses through the given Beam pipeline to construct a DAG of Beam Transform, + * while preserving hierarchy of CompositeTransforms. + * This DAG will be later translated by {@link PipelineTranslator} into Nemo IR DAG. + */ +public final class PipelineVisitor extends Pipeline.PipelineVisitor.Defaults { + + private static final String TRANSFORM = "Transform-"; + private static final String DATAFLOW = "Dataflow-"; + + private final Stack<CompositeTransformVertex> compositeTransformVertexStack = new Stack<>(); + private CompositeTransformVertex rootVertex = null; + private int nextIdx = 0; + + @Override + public void visitPrimitiveTransform(final TransformHierarchy.Node node) { + final PrimitiveTransformVertex vertex = new PrimitiveTransformVertex(node, compositeTransformVertexStack.peek()); + compositeTransformVertexStack.peek().addVertex(vertex); + vertex.getPValuesConsumed() + .forEach(pValue -> { + final TransformVertex dst = getDestinationOfDataFlowEdge(vertex, pValue); + dst.parent.addDataFlow(new DataFlowEdge(dst.parent.getProducerOf(pValue), dst)); + }); + } + + @Override + public CompositeBehavior enterCompositeTransform(final TransformHierarchy.Node node) { + final CompositeTransformVertex vertex; + if (compositeTransformVertexStack.isEmpty()) { + // There is always a top-level CompositeTransform that encompasses the entire Beam pipeline. + vertex = new CompositeTransformVertex(node, null); + } else { + vertex = new CompositeTransformVertex(node, compositeTransformVertexStack.peek()); + } + compositeTransformVertexStack.push(vertex); + return CompositeBehavior.ENTER_TRANSFORM; + } + + @Override + public void leaveCompositeTransform(final TransformHierarchy.Node node) { + final CompositeTransformVertex vertex = compositeTransformVertexStack.pop(); + vertex.build(); + if (compositeTransformVertexStack.isEmpty()) { + // The vertex is the root. + if (rootVertex != null) { + throw new RuntimeException("The visitor already have traversed a Beam pipeline. " + + "Re-using a visitor is not allowed."); + } + rootVertex = vertex; + } else { + // The CompositeTransformVertex is ready; adding it to its parent vertex. + compositeTransformVertexStack.peek().addVertex(vertex); + } + } + + /** + * @return A vertex representing the top-level CompositeTransform. + */ + public CompositeTransformVertex getConvertedPipeline() { + if (rootVertex == null) { + throw new RuntimeException("The visitor have not fully traversed through a Beam pipeline."); + } + return rootVertex; + } + + /** + * Represents a {@link org.apache.beam.sdk.transforms.PTransform} as a vertex in DAG. + */ + public abstract class TransformVertex extends Vertex { Review comment: My understanding of this change is that - Before: (Beam) TransformHierarchy.Node -> (Nemo) IRVertex - After: (Beam) TransformHierarchy.Node -> (Nemo) TransformVertex(Primitive/Composite) -> (Nemo) IRVertex In the previous method, we are in the 'eager mode' going directly from a Beam primitive transform to an IRVertex without much considerations for Beam's composite transforms. In this new approach, we are in the 'lazy mode' where we create another full intermediary DAG, and conveniently translate composite transforms using our `CompositeTransformVertex` abstraction. I like how the new approach enables grouping multiple Beam primitive transforms belonging to the same Beam composite transform. However, I think that a 'hybrid mode' where we lazily construct composite transforms with a group of primitive transforms, but eagerly translate each composite transform upon `leaveCompositeTransform` may be an option to achieve the same effects with less code (i.e., without another DAG). For example, we may be able to make `CompositeTransformVertex` directly reference a DAG of Beam transforms or a DAG of Nemo IRVertex, and immediately translate that into an appropriate IRVertex DAG upon `leaveCompositeTransform`. (without introducing `PrimitiveTransformVertex` and `DataFlowEdge`) The rationale for this is to keep the role of the additional abstraction fairly small and reuse the existing Beam DAG/Nemo DAG as much as possible. Let me know what you think about this! ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
