001/*
002 * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.flow.hadoop.planner.rule.expression;
022
023import cascading.flow.planner.iso.expression.ElementCapture;
024import cascading.flow.planner.iso.expression.ExpressionGraph;
025import cascading.flow.planner.iso.expression.FlowElementExpression;
026import cascading.flow.planner.iso.expression.PathScopeExpression;
027import cascading.flow.planner.rule.RuleExpression;
028import cascading.flow.planner.rule.expressiongraph.SyncPipeExpressionGraph;
029import cascading.pipe.Group;
030import cascading.pipe.HashJoin;
031import cascading.pipe.Pipe;
032
033/**
034 * This rule is a compliment to GroupNonBlockingHashJoinTransformRule and is intended
035 * to prevent a HashJoin from landing in a Reducer until reduce side HashJoins are supported.
036 */
037public class BalanceGroupNonBlockingHashJoinExpression extends RuleExpression
038  {
039  public BalanceGroupNonBlockingHashJoinExpression()
040    {
041    super(
042      new SyncPipeExpressionGraph(),
043
044      new ExpressionGraph()
045        .arc(
046          new FlowElementExpression( Group.class ),
047          PathScopeExpression.NON_BLOCKING,
048          new FlowElementExpression( HashJoin.class )
049        ),
050
051      new ExpressionGraph()
052        .arc(
053          new FlowElementExpression( ElementCapture.Primary, Pipe.class ),
054          PathScopeExpression.NON_BLOCKING,
055          new FlowElementExpression( HashJoin.class )
056        )
057    );
058    }
059  }