/**
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 Nov 27, 2011
*/
package com.bigdata.rdf.sparql.ast.hints;
import com.bigdata.rdf.sparql.ast.ASTBase;
import com.bigdata.rdf.sparql.ast.QueryHints;
import com.bigdata.rdf.sparql.ast.QueryRoot;
import com.bigdata.rdf.sparql.ast.eval.AST2BOpContext;
/**
* Query hint for turning on/off a distinct filter over the triples extracted
* from the default graph in quads mode.
* <p>
* By default, a DISTINCT filter is applied when evaluating access paths
* against the default graph, for correctness reasons. The hint (or the
* respective system property) can be used to disabled the distinct filter,
* in order to accelerate default graph queries. This can be done whenever
* it is known that NO triple occurs in more than one named graph.
*
* BE CAREFUL: if this condition does not hold and the filter is disabled,
* wrong query results (caused by duplicates) will be the consequence.
*/
final class DefaultGraphDistinctFilterHint extends AbstractBooleanQueryHint {
protected DefaultGraphDistinctFilterHint() {
super(QueryHints.DEFAULT_GRAPH_DISTINCT_FILTER, QueryHints.DEFAULT_DEFAULT_GRAPH_DISTINCT_FILTER);
}
@Override
public void handle(final AST2BOpContext context, final QueryRoot queryRoot,
final QueryHintScope scope, final ASTBase op, final Boolean value) {
switch (scope) {
case Query:
context.defaultGraphDistinctFilter = value;
return;
default:
break;
}
throw new QueryHintException(scope, op, getName(), value);
}
}