/**
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 Aug 28, 2015
*/
package com.bigdata.rdf.sparql.ast.explainhints;
import com.bigdata.rdf.sparql.ast.IGroupMemberNode;
/**
* Explain hint indicating potential problems caused by the join order within
* a given join group, such as non-optional non-minus nodes that could not be
* moved in front of optionals. Such constructs are often undesired and may
* cause performance bottlenecks.
*
* @author <a href="ms@metaphacts.com">Michael Schmidt</a>
* @version $Id$
*/
public class JoinOrderExplainHint extends ExplainHint {
private static final String EXPLAIN_HINT_TYPE = "Join Order";
public static final String ACROSS_PARTITION_REORDERING_PROBLEM =
"The referenced AST node cannot be moved in front of an " +
"OPTIONAL or MINUS expression. Blazegraph tries to do " +
"so in order to assert best performance, but in this " +
"it seems like query semantics might change if we move " +
"the node. Please review your query and move the node to " +
"in front of all OPTIONAL or MINUS nodes manually if " +
"this is what you wanted to implement. Note that this " +
"hint does not imply that your query is wrong, but there " +
"might be a problem with it.";
public JoinOrderExplainHint(
final String explainHintDescription, final IGroupMemberNode candidate) {
super(
explainHintDescription,
EXPLAIN_HINT_TYPE,
ExplainHintCategory.CORRECTNESS,
ExplainHintSeverity.MODERATE,
candidate);
}
}