/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Oct 7, 2011
*/
package com.bigdata.rdf.sparql.ast.optimizers;
import java.util.LinkedList;
import java.util.List;
import com.bigdata.bop.BOp;
import com.bigdata.bop.IBindingSet;
import com.bigdata.rdf.sparql.ast.GroupNodeBase;
import com.bigdata.rdf.sparql.ast.IGroupMemberNode;
import com.bigdata.rdf.sparql.ast.IQueryNode;
import com.bigdata.rdf.sparql.ast.JoinGroupNode;
import com.bigdata.rdf.sparql.ast.NamedSubqueriesNode;
import com.bigdata.rdf.sparql.ast.NamedSubqueryRoot;
import com.bigdata.rdf.sparql.ast.QueryBase;
import com.bigdata.rdf.sparql.ast.QueryNodeWithBindingSet;
import com.bigdata.rdf.sparql.ast.QueryRoot;
import com.bigdata.rdf.sparql.ast.UnionNode;
import com.bigdata.rdf.sparql.ast.eval.AST2BOpContext;
/**
* Flatten nested UNIONs whenever possible.
*
* <pre>
* UNION(A,B,C) := UNION(A,UNION(B,C)) -or- UNION(UNION(A,B),C))
* </pre>
*
* Note: This must run before the {@link ASTEmptyGroupOptimizer} in order to
* eliminate certain UNION/group combinations.
* <p>
* Note: The bigdata SPARQL parser no longer produces this nested UNION
* construction. However, it is possible that other SPARQL parsers or hand
* construction can still produce this nesting pattern, in which case this
* optimizer will flatten out that pattern.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id: ASTFlattenUnionsOptimizer.java 5314 2011-10-12 12:51:13Z
* thompsonbry $
*/
public class ASTFlattenUnionsOptimizer implements IASTOptimizer {
// private static final Logger log = Logger
// .getLogger(ASTFlattenUnionsOptimizer.class);
//
@Override
public QueryNodeWithBindingSet optimize(
final AST2BOpContext context, final QueryNodeWithBindingSet input) {
final IQueryNode queryNode = input.getQueryNode();
final IBindingSet[] bindingSets = input.getBindingSets();
if (!(queryNode instanceof QueryRoot))
return new QueryNodeWithBindingSet(queryNode, bindingSets);
final QueryRoot queryRoot = (QueryRoot) queryNode;
// Main WHERE clause
{
final GroupNodeBase<?> whereClause = (GroupNodeBase<?>) queryRoot
.getWhereClause();
if (whereClause != null) {
flattenUnions(whereClause);
}
}
// Named subqueries
if (queryRoot.getNamedSubqueries() != null) {
final NamedSubqueriesNode namedSubqueries = queryRoot
.getNamedSubqueries();
/*
* Note: This loop uses the current size() and get(i) to avoid
* problems with concurrent modification during visitation.
*/
for (int i = 0; i < namedSubqueries.size(); i++) {
final NamedSubqueryRoot namedSubquery = (NamedSubqueryRoot) namedSubqueries
.get(i);
final GroupNodeBase<?> whereClause = (GroupNodeBase<?>) namedSubquery
.getWhereClause();
if (whereClause != null) {
flattenUnions(whereClause);
}
}
}
// log.error("\nafter rewrite:\n" + queryNode);
return new QueryNodeWithBindingSet(queryNode, bindingSets);
}
/**
*
*
* @param op
*/
private static void flattenUnions(final GroupNodeBase<?> op) {
if ((op instanceof UnionNode)) {
/*
* The direct children of a UnionNode are JoinGroupNodes.
*
* If the direct child of a child JoinGroupNode is a UnionNode, then
* we will lift the child UnionNode's children into this UnionNode
* and eliminate the child JoinGroupNode for this UnionNode which
* was the parent of the lifted UnionNode.
*/
final UnionNode thisUnion = (UnionNode) op;
final List<JoinGroupNode> childrenToRemove = new LinkedList<JoinGroupNode>();
for (int i = 0; i < op.arity(); i++) {
final JoinGroupNode directChild = (JoinGroupNode) op.get(i);
if (directChild.arity() == 1
&& directChild.get(0) instanceof UnionNode) {
final UnionNode childUnion = (UnionNode) directChild.get(0);
/*
* Lift union.
*
* Note: All children MUST be JoinGroupNodes
*/
for (int j = 0; j < childUnion.arity(); j++) {
final JoinGroupNode childToLift = (JoinGroupNode) childUnion
.get(j);
thisUnion.addChild(childToLift);
childrenToRemove.add(directChild);
}
}
}
// Remove any join group nodes for lifted unions.
for(JoinGroupNode directChild : childrenToRemove) {
thisUnion.removeChild(directChild);
}
}
/*
* Recursion, but only into group nodes (including within subqueries).
*/
for (int i = 0; i < op.arity(); i++) {
final BOp child = op.get(i);
if (child instanceof GroupNodeBase<?>) {
final GroupNodeBase<?> childGroup = (GroupNodeBase<?>) child;
flattenUnions(childGroup);
} else if (child instanceof QueryBase) {
final QueryBase subquery = (QueryBase) child;
final GroupNodeBase<IGroupMemberNode> childGroup = (GroupNodeBase<IGroupMemberNode>) subquery
.getWhereClause();
flattenUnions(childGroup);
}
}
}
}