Optimize search for when only one result is required

community/lucene-index/src/main/java/org/neo4j/kernel/api/impl/index/FirstHitCollector.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2002-2015 "Neo Technology,"
+ * Network Engine for Objects in Lund AB [http://neotechnology.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Neo4j 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+package org.neo4j.kernel.api.impl.index;
+
+import org.apache.lucene.search.CollectionTerminatedException;
+import org.apache.lucene.search.SimpleCollector;
+
+import java.io.IOException;
+
+/**
+ * A {@code Collector} that terminates the collection after the very first hit.
+ * As a consequence, additional collectors in this search that require a complete run over the index,
+ * such as {@code TotalHitCountCollector} or {@link DocValuesCollector}, won't work as expected.
+ */
+public final class FirstHitCollector extends SimpleCollector
+{
+    public static final int NO_MATCH = -1;
+
+    private int result = NO_MATCH;
+
+    /**
+     * @return true when this collector got a match, otherwise false.
+     */
+    public boolean hasMatched()
+    {
+        return result != NO_MATCH;
+    }
+
+    /**
+     * @return the docId if this collector got a match, otherwise {@link FirstHitCollector#NO_MATCH}.
+     */
+    public int getMatchedDoc()
+    {
+        return result;
+    }
+
+    @Override
+    public void collect( int doc ) throws IOException
+    {
+        result = doc;
+        throw new CollectionTerminatedException();
+    }
+
+    @Override
+    public boolean needsScores()
+    {
+        return false;
+    }
+}

community/lucene-index/src/main/java/org/neo4j/kernel/api/impl/index/LuceneLabelScanWriter.java

@@ -24,7 +24,6 @@
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.TermQuery;
-import org.apache.lucene.search.TopDocs;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -110,12 +109,14 @@ public void close() throws IOException
 
     private Map<Long/*range*/, Bitmap> readLabelBitMapsInRange( IndexSearcher searcher, long range ) throws IOException
     {
-        Map<Long/*label*/, Bitmap> fields = new HashMap<>();
+        Map<Long/*label*/,Bitmap> fields = new HashMap<>();
         Term documentTerm = format.rangeTerm( range );
-        TopDocs docs = searcher.search( new TermQuery( documentTerm ), 1 );
-        if ( docs != null && docs.totalHits != 0 )
+        TermQuery query = new TermQuery( documentTerm );
+        FirstHitCollector hitCollector = new FirstHitCollector();
+        searcher.search( query, hitCollector );
+        if ( hitCollector.hasMatched() )
         {
-            Document document = searcher.doc( docs.scoreDocs[0].doc );
+            Document document = searcher.doc( hitCollector.getMatchedDoc() );
             for ( IndexableField field : document.getFields() )
             {
                 if ( !format.isRangeField( field ) )