/**
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 4, 2008
*/
package com.bigdata.rdf.spo;
import com.bigdata.btree.ITuple;
import com.bigdata.btree.filter.Advancer;
import com.bigdata.btree.keys.IKeyBuilder;
import com.bigdata.btree.keys.KeyBuilder;
import com.bigdata.btree.keys.SuccessorUtil;
import com.bigdata.rdf.internal.IV;
import com.bigdata.rdf.internal.IVUtility;
import com.bigdata.relation.accesspath.IAccessPath;
import com.bigdata.striterator.IKeyOrder;
/**
* This was cloned from the {@link DistinctTermAdvancer}. It supports an
* efficient scan of the distinct term identifiers that appear in the first
* position(s) of the keys for the statement index corresponding to the
* specified {@link IKeyOrder}. For example, using {@link SPOKeyOrder#POS} will
* give you the term identifiers for the distinct predicates actually in use
* within statements in the {@link SPORelation}.
* <p>
* Note: This class only offers additional functionality over the
* {@link DistinctTermAdvancer} for a quad store. For example, consider a triple
* store with 2-bound on the {@link SPOKeyOrder#SPO} index. Since you are only
* going to visit the distinct Object values, the advancer will not "advance"
* over anything and you might as well use a normal {@link IAccessPath} or
* rangeIterator.
*
* @see DistinctTermAdvancer
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id: DistinctMultiTermAdvancer.java 2886 2010-05-19 19:16:49Z
* mroycsi $
*
* @todo Unit tests?
*/
public class DistinctMultiTermAdvancer extends Advancer<SPO> {
// private static final long serialVersionUID = 2500001864793869957L;
/**
* New version for this class, which
*/
private static final long serialVersionUID = -7326621294779476500L;
private final int arity;
private final int boundEntries;
private transient IKeyBuilder keyBuilder;
public DistinctMultiTermAdvancer(final int arity, final int boundEntries) {
this.arity = arity;
this.boundEntries = boundEntries;
}
@Override
protected void advance(final ITuple<SPO> tuple) {
if (keyBuilder == null) {
/*
* Note: It appears that you can not set this either implicitly or
* explicitly during ctor initialization if you want it to exist
* during de-serialization. Hence it is initialized lazily here.
* This is Ok since the iterator pattern is single threaded.
*/
keyBuilder = KeyBuilder.newInstance();
}
final byte[] key = tuple.getKey();
final IV[] ivs = IVUtility.decode(key, boundEntries+1);
keyBuilder.reset();
for (int i = 0; i < ivs.length; i++) {
ivs[i].encode(keyBuilder);
}
final byte[] fromKey = keyBuilder.getKey();
final byte[] toKey = SuccessorUtil.successor(fromKey.clone());
src.seek(toKey);
}
}