/*
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.ITupleCursor;
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.IVUtility;
import com.bigdata.rdf.store.IRawTripleStore;
import com.bigdata.relation.accesspath.AccessPath;
/**
* Advances the source {@link ITupleCursor} through the distinct term
* identifiers for some {@link AccessPath}. Each time a new
* {@link ITuple} is visited, the term identifier for the first position in
* that tuple is decoded and its successor is formed. The source
* {@link ITupleCursor} is then advanced to the key having that term
* identifier in its first position and {@link IRawTripleStore#NULL} in its
* 2nd and 3rd position. For example, if the {@link ITupleCursor} visits an
* {@link ITuple} whose term identifiers are, in the order in which they
* appear in the key:
*
* <pre>
* [ 12, 4, 44 ]
* </pre>
*
* Then the source {@link ITupleCursor} will be advanced to the key:
*
* <pre>
* [ 13, 0, 0 ]
* </pre>
*
* This is used to efficiently visit the distinct terms actually appearing
* in the subject, predicate, or object position of {@link SPO}s in the
* database.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
*/
public class DistinctTermAdvancer extends Advancer<SPO> {
private static final long serialVersionUID = 2500001864793869957L;
// private final int arity;
private transient IKeyBuilder keyBuilder;
public DistinctTermAdvancer(final int arityIsIgnored) {
// this.arity = arity;
}
@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.
*/
// assert arity == 3 || arity == 4;
keyBuilder = KeyBuilder.newInstance();
}
/*
* new approach.
*/
final byte[] key = tuple.getKey();
keyBuilder.reset();
IVUtility.decode(key).encode(keyBuilder);
final byte[] fromKey = keyBuilder.getKey();
final byte[] toKey = SuccessorUtil.successor(fromKey.clone());
src.seek(toKey);
}
}