/*
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 20, 2008
*/
package com.bigdata.bop.joinGraph;
import org.apache.log4j.Logger;
import com.bigdata.bop.IPredicate;
import com.bigdata.relation.IRelation;
import com.bigdata.relation.accesspath.IAccessPath;
import com.bigdata.relation.rule.eval.IJoinNexus;
/**
* Default implementation.
*
* @todo use a cache per relation and timestamp. Track the actual range counts
* for a predicate as bound in a query vs those predicated for the
* predicate. The actual counts can also vary if the backchainer is turned
* on since that is not reflected in the non-exact range count. We can
* store range counts efficiently in a B+Tree using a key formed from the
* {s:p:o} and using 0L for a variable.
* <p>
* perhaps it would be worth while to turn off the range count metadata
* for some of the indices, e.g., the reverse lexicon does not need this
* and perhaps the justifications index does not need it either. That is a
* performance boost of ~8% if I recall.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class DefaultRangeCountFactory implements IRangeCountFactory {
protected static final transient Logger log = Logger
.getLogger(DefaultRangeCountFactory.class);
protected static final transient boolean DEBUG = log.isDebugEnabled();
private final IJoinNexus joinNexus;
public DefaultRangeCountFactory(final IJoinNexus joinNexus) {
if (joinNexus == null)
throw new IllegalArgumentException();
this.joinNexus = joinNexus;
}
/**
* Return the range count for the predicate. The range counts are requested
* using the "non-exact" range count query, so the range counts are actually
* the upper bound. However, if the upper bound is ZERO (0) then the range
* count really is ZERO (0).
*
* @param tailIndex
* The index of the predicate in the tail of the rule.
*
* @return The range count for that tail predicate.
*/
public long rangeCount(final IPredicate predicate) {
final IRelation relation = joinNexus.getTailRelationView(predicate);
final IAccessPath accessPath = joinNexus.getTailAccessPath(relation,
predicate);
final long rangeCount = accessPath.rangeCount(false/* exact */);
if (DEBUG) {
/*
* @todo trace total time in range counts while generating the plan
* or just track the total time to generate the plan, which should
* be dominated by the range count time. if this adds too much
* latency then consider other approaches to optimization.
*/
log.debug("rangeCount=" + rangeCount + ", tail=" + predicate
+ ", accessPath=" + accessPath);
}
return rangeCount;
}
}