GH-1405 query planner uses hashjoin when scoped group pattern

queryalgebra-model/src/main/java/org/eclipse/rdf4j/query/algebra/AbstractQueryModelNode.java

@@ -15,7 +15,7 @@
 /**
  * Base implementation of {@link QueryModelNode}.
  */
-public abstract class AbstractQueryModelNode implements QueryModelNode {
+public abstract class AbstractQueryModelNode implements QueryModelNode, GraphPatternGroupable {
 
 	/*-----------*
 	 * Variables *
@@ -25,6 +25,8 @@ public abstract class AbstractQueryModelNode implements QueryModelNode {
 
 	private QueryModelNode parent;
 
+	private boolean isGraphPatternGroup;
+
 	/*---------*
 	 * Methods *
 	 *---------*/
@@ -39,6 +41,26 @@ public void setParentNode(QueryModelNode parent) {
 		this.parent = parent;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see org.eclipse.rdf4j.query.algebra.GraphPatternGroupable#isGraphPatternGroup()
+	 */
+	@Override
+	public boolean isGraphPatternGroup() {
+		return isGraphPatternGroup;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see org.eclipse.rdf4j.query.algebra.GraphPatternGroupable#setGraphPatternGroup(boolean)
+	 */
+	@Override
+	public void setGraphPatternGroup(boolean isGraphPatternGroup) {
+		this.isGraphPatternGroup = isGraphPatternGroup;
+	}
+
 	/**
 	 * Dummy implementation of {@link QueryModelNode#visitChildren} that does nothing. Subclasses should override this
 	 * method when they have child nodes.

queryalgebra-model/src/main/java/org/eclipse/rdf4j/query/algebra/GraphPatternGroupable.java

@@ -0,0 +1,34 @@
+/*******************************************************************************
+ * Copyright (c) 2019 Eclipse RDF4J contributors.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Distribution License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *******************************************************************************/
+package org.eclipse.rdf4j.query.algebra;
+
+/**
+ * {@link QueryModelNode}s that can represent a full graph pattern group.
+ * 
+ * Although the notion of a graph pattern group is strictly not relevant at the algebra level, it gives an indication to
+ * evaluation strategy implementations on how they can optimize join patterns wrt variable scope.
+ * 
+ * @author Jeen Broekstra
+ *
+ */
+public interface GraphPatternGroupable {
+
+	/**
+	 * indicates if the node represents the root of a graph pattern group.
+	 * 
+	 * @return true iff the node represents the node of a graph pattern group.
+	 *
+	 */
+	public boolean isGraphPatternGroup();
+
+	/**
+	 * Set the value of {@link #isGraphPatternGroup()} to true or false.
+	 */
+	public void setGraphPatternGroup(boolean isGraphPatternGroup);
+
+}

queryalgebra-model/src/main/java/org/eclipse/rdf4j/query/algebra/UnaryTupleOperator.java

@@ -12,7 +12,7 @@
 /**
  * An abstract superclass for unary tuple operators which, by definition, has one argument.
  */
-public abstract class UnaryTupleOperator extends AbstractQueryModelNode implements TupleExpr {
+public abstract class UnaryTupleOperator extends AbstractQueryModelNode implements TupleExpr, GraphPatternGroupable {
 
 	/*-----------*
 	 * Variables *
@@ -23,6 +23,8 @@ public abstract class UnaryTupleOperator extends AbstractQueryModelNode implemen
 	 */
 	protected TupleExpr arg;
 
+	private boolean isGraphPatternGroup;
+
 	/*--------------*
 	 * Constructors *
 	 *--------------*/
@@ -43,6 +45,16 @@ public UnaryTupleOperator(TupleExpr arg) {
 	 * Methods *
 	 *---------*/
 
+	@Override
+	public boolean isGraphPatternGroup() {
+		return isGraphPatternGroup;
+	}
+
+	@Override
+	public void setGraphPatternGroup(boolean isGraphPatternGroup) {
+		this.isGraphPatternGroup = isGraphPatternGroup;
+	}
+
 	/**
 	 * Gets the argument of this unary tuple operator.
 	 * 

queryalgebra-model/src/main/java/org/eclipse/rdf4j/query/algebra/helpers/TupleExprs.java

@@ -15,6 +15,7 @@
 import org.eclipse.rdf4j.model.BNode;
 import org.eclipse.rdf4j.model.Literal;
 import org.eclipse.rdf4j.model.Value;
+import org.eclipse.rdf4j.query.algebra.GraphPatternGroupable;
 import org.eclipse.rdf4j.query.algebra.Join;
 import org.eclipse.rdf4j.query.algebra.Projection;
 import org.eclipse.rdf4j.query.algebra.QueryModelNode;
@@ -55,6 +56,20 @@ public static boolean containsSubquery(TupleExpr t) {
 		return false;
 	}
 
+	/**
+	 * Verifies if the supplied {@link TupleExpr} represents a group graph pattern.
+	 * 
+	 * @param expr a {@link TupleExpr}
+	 * @return <code>true</code> if the {@link TupleExpr} is {@link GraphPatternGroupable} and has its graph pattern
+	 *         group flag set to <code>true</code>, <code>false</code> otherwise.
+	 */
+	public static boolean isGraphPatternGroup(TupleExpr expr) {
+		if (expr instanceof GraphPatternGroupable) {
+			return ((GraphPatternGroupable) expr).isGraphPatternGroup();
+		}
+		return false;
+	}
+
 	/**
 	 * Verifies if the supplied {@link TupleExpr} contains a {@link Projection}. If the supplied TupleExpr is a
 	 * {@link Join} or contains a {@link Join}, projections inside that Join's arguments will not be taken into account.

queryparser/sparql/src/main/java/org/eclipse/rdf4j/query/parser/sparql/GraphPattern.java

@@ -164,13 +164,7 @@ public TupleExpr buildTupleExpr() {
 
 			for (int i = 1; i < requiredTEs.size(); i++) {
 				TupleExpr te = requiredTEs.get(i);
-				// if (containsProjection(te) || containsProjection(result))
-				// {
-				// result = new BottomUpJoin(result, te);
-				// }
-				// else {
 				result = new Join(result, te);
-				// }
 			}
 		}
 

queryparser/sparql/src/main/java/org/eclipse/rdf4j/query/parser/sparql/TupleExprBuilder.java

@@ -47,6 +47,7 @@
 import org.eclipse.rdf4j.query.algebra.ExtensionElem;
 import org.eclipse.rdf4j.query.algebra.Filter;
 import org.eclipse.rdf4j.query.algebra.FunctionCall;
+import org.eclipse.rdf4j.query.algebra.GraphPatternGroupable;
 import org.eclipse.rdf4j.query.algebra.Group;
 import org.eclipse.rdf4j.query.algebra.GroupConcat;
 import org.eclipse.rdf4j.query.algebra.GroupElem;
@@ -1023,6 +1024,8 @@ public Object visit(ASTGraphPatternGroup node, Object data) throws VisitorExcept
 		// bindings external to the group
 		TupleExpr te = graphPattern.buildTupleExpr();
 
+		((GraphPatternGroupable) te).setGraphPatternGroup(true);
+
 		parentGP.addRequiredTE(te);
 
 		graphPattern = parentGP;