Index: lucene/facet/src/test/org/apache/lucene/facet/search/TestDrillSideways.java
===================================================================
--- lucene/facet/src/test/org/apache/lucene/facet/search/TestDrillSideways.java	(revision 1470728)
+++ lucene/facet/src/test/org/apache/lucene/facet/search/TestDrillSideways.java	(working copy)
@@ -642,6 +642,7 @@
       String[][] drillDowns = new String[numDims][];
 
       int count = 0;
+      boolean anyMultiValuedDrillDowns = false;
       while (count < numDrillDown) {
         int dim = random().nextInt(numDims);
         if (drillDowns[dim] == null) {
@@ -651,6 +652,7 @@
           } else {
             int orCount = _TestUtil.nextInt(random(), 1, Math.min(5, dimValues[dim].length));
             drillDowns[dim] = new String[orCount];
+            anyMultiValuedDrillDowns |= orCount > 1;
             for(int i=0;i<orCount;i++) {
               while (true) {
                 String value = dimValues[dim][random().nextInt(dimValues[dim].length)];
@@ -749,6 +751,22 @@
                              }
                            }, fsp);
 
+      // Also separately verify that DS respects the
+      // scoreSubDocsAtOnce method, to ensure that all
+      // subScorers are on the same docID:
+      if (!anyMultiValuedDrillDowns) {
+        // Can only do this test when there are no OR'd
+        // drill-down values, beacuse in that case it's
+        // easily possible for one of the DD terms to be on
+        // a future docID:
+        new DrillSideways(s, tr) {
+          @Override
+          protected boolean scoreSubDocsAtOnce() {
+            return true;
+          }
+        }.search(ddq, new AssertingSubDocsAtOnceCollector(), fsp);
+      }
+
       SimpleFacetResult expected = slowDrillSidewaysSearch(s, requests, docs, contentToken, drillDowns, dimValues, filter);
 
       Sort sort = new Sort(new SortField("id", SortField.Type.STRING));
Index: lucene/facet/src/test/org/apache/lucene/facet/search/AssertingSubDocsAtOnceCollector.java
===================================================================
--- lucene/facet/src/test/org/apache/lucene/facet/search/AssertingSubDocsAtOnceCollector.java	(revision 0)
+++ lucene/facet/src/test/org/apache/lucene/facet/search/AssertingSubDocsAtOnceCollector.java	(working copy)
@@ -0,0 +1,67 @@
+package org.apache.lucene.facet.search;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.lucene.index.AtomicReaderContext;
+import org.apache.lucene.search.Collector;
+import org.apache.lucene.search.Scorer.ChildScorer;
+import org.apache.lucene.search.Scorer;
+
+/** Verifies in collect() that all child subScorers are on
+ *  the collected doc. */
+class AssertingSubDocsAtOnceCollector extends Collector {
+
+  // TODO: allow wrapping another Collector
+
+  List<Scorer> allScorers;
+
+  @Override
+  public void setScorer(Scorer s) {
+    // Gathers all scorers, including s and "under":
+    allScorers = new ArrayList<Scorer>();
+    allScorers.add(s);
+    int upto = 0;
+    while(upto < allScorers.size()) {
+      s = allScorers.get(upto++);
+      for (ChildScorer sub : s.getChildren()) {
+        allScorers.add(sub.child);
+      }
+    }
+  }
+
+  @Override
+  public void collect(int docID) {
+    for(Scorer s : allScorers) {
+      if (docID != s.docID()) {
+        throw new IllegalStateException("subScorer=" + s + " has docID=" + s.docID() + " != collected docID=" + docID);
+      }
+    }
+  }
+
+  @Override
+  public void setNextReader(AtomicReaderContext context) {
+  }
+
+  @Override
+  public boolean acceptsDocsOutOfOrder() {
+    return false;
+  }
+}

Property changes on: lucene/facet/src/test/org/apache/lucene/facet/search/AssertingSubDocsAtOnceCollector.java
___________________________________________________________________
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Index: lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysQuery.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysQuery.java	(revision 1470728)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysQuery.java	(working copy)
@@ -39,12 +39,14 @@
   final Collector drillDownCollector;
   final Collector[] drillSidewaysCollectors;
   final Term[][] drillDownTerms;
+  final boolean scoreSubDocsAtOnce;
 
-  DrillSidewaysQuery(Query baseQuery, Collector drillDownCollector, Collector[] drillSidewaysCollectors, Term[][] drillDownTerms) {
+  DrillSidewaysQuery(Query baseQuery, Collector drillDownCollector, Collector[] drillSidewaysCollectors, Term[][] drillDownTerms, boolean scoreSubDocsAtOnce) {
     this.baseQuery = baseQuery;
     this.drillDownCollector = drillDownCollector;
     this.drillSidewaysCollectors = drillSidewaysCollectors;
     this.drillDownTerms = drillDownTerms;
+    this.scoreSubDocsAtOnce = scoreSubDocsAtOnce;
   }
 
   @Override
@@ -65,7 +67,7 @@
     if (newQuery == baseQuery) {
       return this;
     } else {
-      return new DrillSidewaysQuery(newQuery, drillDownCollector, drillSidewaysCollectors, drillDownTerms);
+      return new DrillSidewaysQuery(newQuery, drillDownCollector, drillSidewaysCollectors, drillDownTerms, scoreSubDocsAtOnce);
     }
   }
   
@@ -152,7 +154,7 @@
 
         return new DrillSidewaysScorer(this, context,
                                        baseScorer,
-                                       drillDownCollector, dims);
+                                       drillDownCollector, dims, scoreSubDocsAtOnce);
       }
     };
   }
Index: lucene/facet/src/java/org/apache/lucene/facet/search/DrillSideways.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/DrillSideways.java	(revision 1470728)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/DrillSideways.java	(working copy)
@@ -209,7 +209,7 @@
       drillSidewaysCollectors[idx++] = FacetsCollector.create(getDrillSidewaysAccumulator(dim, new FacetSearchParams(fsp.indexingParams, requests)));
     }
 
-    DrillSidewaysQuery dsq = new DrillSidewaysQuery(baseQuery, drillDownCollector, drillSidewaysCollectors, drillDownTerms);
+    DrillSidewaysQuery dsq = new DrillSidewaysQuery(baseQuery, drillDownCollector, drillSidewaysCollectors, drillDownTerms, scoreSubDocsAtOnce());
 
     searcher.search(dsq, hitCollector);
 
@@ -300,6 +300,19 @@
     return FacetsAccumulator.create(fsp, searcher.getIndexReader(), taxoReader);
   }
 
+  /** Override this and return true if your collector
+   *  (e.g., ToParentBlockJoinCollector) expects all
+   *  sub-scorers to be positioned on the document being
+   *  collected.  This will cause some performance loss;
+   *  default is false.  Note that if you return true from
+   *  this method (in a subclass) be sure your collector
+   *  also returns false from {@link
+   *  Collector#acceptsDocsOutOfOrder}: this will trick
+   *  BooleanQuery into also scoring all subDocs at once. */
+  protected boolean scoreSubDocsAtOnce() {
+    return false;
+  }
+
   /** Represents the returned result from a drill sideways
    *  search. */
   public static class DrillSidewaysResult {
Index: lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysScorer.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysScorer.java	(revision 1470728)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/DrillSidewaysScorer.java	(working copy)
@@ -43,17 +43,19 @@
 
   private static final int CHUNK = 2048;
   private static final int MASK = CHUNK-1;
+  private final boolean scoreSubDocsAtOnce;
 
   private int collectDocID = -1;
   private float collectScore;
 
   DrillSidewaysScorer(Weight w, AtomicReaderContext context, Scorer baseScorer, Collector drillDownCollector,
-                      DocsEnumsAndFreq[] dims) {
+                      DocsEnumsAndFreq[] dims, boolean scoreSubDocsAtOnce) {
     super(w);
     this.dims = dims;
     this.context = context;
     this.baseScorer = baseScorer;
     this.drillDownCollector = drillDownCollector;
+    this.scoreSubDocsAtOnce = scoreSubDocsAtOnce;
   }
 
   @Override
@@ -77,7 +79,6 @@
 
     // Position all scorers to their first matching doc:
     int baseDocID = baseScorer.nextDoc();
-
     for(DocsEnumsAndFreq dim : dims) {
       for(DocsEnum docsEnum : dim.docsEnums) {
         if (docsEnum != null) {
@@ -101,7 +102,7 @@
     int estBaseHitCount = context.reader().maxDoc() / (1+baseDocID);
 
     /*
-    System.out.println("\nbaseDocID=" + baseDocID + " est=" + estBaseHitCount);
+    System.out.println("\nbaseDocID=" + baseScorer.docID() + " est=" + estBaseHitCount);
     System.out.println("  maxDoc=" + context.reader().maxDoc());
     System.out.println("  maxFreq=" + maxFreq);
     System.out.println("  dims[0].freq=" + dims[0].freq);
@@ -110,15 +111,22 @@
     }
     */
 
-    if (estBaseHitCount < maxFreq/10) {
+    //System.out.println("DS score " + scoreSubDocsAtOnce);
+    if (!scoreSubDocsAtOnce) {
+      if (estBaseHitCount < maxFreq/10) {
+        //System.out.println("baseAdvance");
+        doBaseAdvanceScoring(collector, docsEnums, sidewaysCollectors);
+      } else if (numDims > 1 && (dims[1].freq < estBaseHitCount/10)) {
+        //System.out.println("drillDownAdvance");
+        doDrillDownAdvanceScoring(collector, docsEnums, sidewaysCollectors);
+      } else {
+        //System.out.println("union");
+        doUnionScoring(collector, docsEnums, sidewaysCollectors);
+      }
+    } else {
+      // TODO: we should fallback to BS2 ReqOptSum scorer here
       //System.out.println("baseAdvance");
       doBaseAdvanceScoring(collector, docsEnums, sidewaysCollectors);
-    } else if (numDims > 1 && (dims[1].freq < estBaseHitCount/10)) {
-      //System.out.println("drillDownAdvance");
-      doDrillDownAdvanceScoring(collector, docsEnums, sidewaysCollectors);
-    } else {
-      //System.out.println("union");
-      doUnionScoring(collector, docsEnums, sidewaysCollectors);
     }
   }