Index: lucene/contrib/queries/src/java/org/apache/lucene/search/SlowCollatedStringComparator.java
--- lucene/contrib/queries/src/java/org/apache/lucene/search/SlowCollatedStringComparator.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/contrib/queries/src/java/org/apache/lucene/search/SlowCollatedStringComparator.java	Fri Jun 10 19:38:21 2011 -0400
@@ -33,7 +33,7 @@
  * This class will be removed in Lucene 5.0
  */
 @Deprecated
-public final class SlowCollatedStringComparator extends FieldComparator {
+public final class SlowCollatedStringComparator extends FieldComparator<BytesRef> {
 
   private final String[] values;
   private DocTerms currentDocTerms;
@@ -99,8 +99,22 @@
   }
 
   @Override
-  public Comparable<?> value(int slot) {
+  public BytesRef value(int slot) {
     final String s = values[slot];
     return s == null ? null : new BytesRef(values[slot]);
   }
+
+  @Override
+  public int compareValues(BytesRef first, BytesRef second) {
+    if (first == null) {
+      if (second == null) {
+        return 0;
+      }
+      return -1;
+    } else if (second == null) {
+      return 1;
+    } else {
+      return collator.compare(first, second);
+    }
+  }
 }
Index: lucene/contrib/spatial/src/java/org/apache/lucene/spatial/tier/DistanceFieldComparatorSource.java
--- lucene/contrib/spatial/src/java/org/apache/lucene/spatial/tier/DistanceFieldComparatorSource.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/contrib/spatial/src/java/org/apache/lucene/spatial/tier/DistanceFieldComparatorSource.java	Fri Jun 10 19:38:21 2011 -0400
@@ -31,94 +31,91 @@
  */
 public class DistanceFieldComparatorSource extends FieldComparatorSource {
 
-	private DistanceFilter distanceFilter;
-	private DistanceScoreDocLookupComparator dsdlc;
+  private DistanceFilter distanceFilter;
+  private DistanceScoreDocLookupComparator dsdlc;
 
-	public DistanceFieldComparatorSource(Filter distanceFilter) {
+  public DistanceFieldComparatorSource(Filter distanceFilter) {
+    this.distanceFilter = (DistanceFilter) distanceFilter;
+  }
 
-		this.distanceFilter = (DistanceFilter) distanceFilter;
+  public void cleanUp() {
+    distanceFilter = null;
 
-	}
+    if (dsdlc != null) {
+      dsdlc.cleanUp();
+    }
 
-	public void cleanUp() {
-		distanceFilter = null;
+    dsdlc = null;
+  }
 
-		if (dsdlc != null)
-			dsdlc.cleanUp();
+  @Override
+  public FieldComparator newComparator(String fieldname, int numHits,
+                                         int sortPos, boolean reversed) throws IOException {
+    dsdlc = new DistanceScoreDocLookupComparator(numHits);
+    return dsdlc;
+  }
 
-		dsdlc = null;
-	}
+  private class DistanceScoreDocLookupComparator extends FieldComparator<Double> {
 
-	@Override
-	public FieldComparator newComparator(String fieldname, int numHits,
-			int sortPos, boolean reversed) throws IOException {
-		dsdlc = new DistanceScoreDocLookupComparator(numHits);
-		return dsdlc;
-	}
+    private double[] values;
+    private double bottom;
+    private int offset =0;
+		
+    public DistanceScoreDocLookupComparator(int numHits) {
+      values = new double[numHits];
+      return;
+    }
 
-	private class DistanceScoreDocLookupComparator extends FieldComparator {
+    @Override
+    public int compare(int slot1, int slot2) {
+      double a = values[slot1];
+      double b = values[slot2];
+      if (a > b)
+        return 1;
+      if (a < b)
+        return -1;
 
-		private double[] values;
-		private double bottom;
-		private int offset =0;
-		
-		public DistanceScoreDocLookupComparator(int numHits) {
-			values = new double[numHits];
-			return;
-		}
+      return 0;
+    }
 
-		@Override
-		public int compare(int slot1, int slot2) {
-			double a = values[slot1];
-			double b = values[slot2];
-			if (a > b)
-				return 1;
-			if (a < b)
-				return -1;
+    public void cleanUp() {
+      distanceFilter = null;
+    }
 
-			return 0;
-		}
+    @Override
+    public int compareBottom(int doc) {
+      double v2 = distanceFilter.getDistance(doc+ offset);
+			
+      if (bottom > v2) {
+        return 1;
+      } else if (bottom < v2) {
+        return -1;
+      }
+      return 0;
+    }
 
-		public void cleanUp() {
-			distanceFilter = null;
-		}
+    @Override
+    public void copy(int slot, int doc) {
+      values[slot] = distanceFilter.getDistance(doc + offset);
+    }
 
-		@Override
-		public int compareBottom(int doc) {
-			double v2 = distanceFilter.getDistance(doc+ offset);
-			
-			if (bottom > v2) {
-				return 1;
-			} else if (bottom < v2) {
-				return -1;
-			}
-			return 0;
-		}
-
-		@Override
-		public void copy(int slot, int doc) {
-			values[slot] = distanceFilter.getDistance(doc + offset);
-		}
-
-		@Override
-		public void setBottom(int slot) {
-			this.bottom = values[slot];
-
-		}
+    @Override
+    public void setBottom(int slot) {
+      this.bottom = values[slot];
+    }
 
     @Override
     public FieldComparator setNextReader(AtomicReaderContext context)
-        throws IOException {
+      throws IOException {
       // each reader in a segmented base
       // has an offset based on the maxDocs of previous readers
       offset = context.docBase;
       return this;
     }
 
-		@Override
-		public Comparable<Double> value(int slot) {
-			return values[slot];
-		}
-	}
-
+    @Override
+    public Double value(int slot) {
+      return values[slot];
+    }
+  }
 }
Index: lucene/src/java/org/apache/lucene/search/FieldComparator.java
--- lucene/src/java/org/apache/lucene/search/FieldComparator.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/FieldComparator.java	Fri Jun 10 19:38:21 2011 -0400
@@ -96,7 +96,7 @@
  *
  * @lucene.experimental
  */
-public abstract class FieldComparator {
+public abstract class FieldComparator<T> {
 
   /**
    * Compare hit at slot1 with hit at slot2.
@@ -176,13 +176,21 @@
    * Return the actual value in the slot.
    *
    * @param slot the value
-   * @return value in this slot upgraded to Comparable
+   * @return value in this slot
    */
-  public abstract Comparable<?> value(int slot);
+  public abstract T value(int slot);
 
-    
+  /** Returns -1 if first is less than second.  Default
+   *  impl to assume the type implements Comparable and
+   *  invoke .compareTo; be sure to override this method if
+   *  your FieldComparator's type isn't a Comparable or
+   *  if your values may sometimes be null */
+  @SuppressWarnings("unchecked")
+  public int compareValues(T first, T second) {
+    return ((Comparable<T>) first).compareTo(second);
+  }
 
-  public static abstract class NumericComparator<T extends CachedArray> extends FieldComparator {
+  public static abstract class NumericComparator<T extends CachedArray, U extends Number> extends FieldComparator<U> {
     protected final CachedArrayCreator<T> creator;
     protected T cached;
     protected final boolean checkMissing;
@@ -203,7 +211,7 @@
 
   /** Parses field's values as byte (using {@link
    *  FieldCache#getBytes} and sorts by ascending value */
-  public static final class ByteComparator extends NumericComparator<ByteValues> {
+  public static final class ByteComparator extends NumericComparator<ByteValues,Byte> {
     private byte[] docValues;
     private final byte[] values;
     private final byte missingValue;
@@ -252,7 +260,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Byte value(int slot) {
       return Byte.valueOf(values[slot]);
     }
   }
@@ -260,13 +268,12 @@
   
   /** Parses field's values as double (using {@link
    *  FieldCache#getDoubles} and sorts by ascending value */
-  public static final class DoubleComparator extends NumericComparator<DoubleValues> {
+  public static final class DoubleComparator extends NumericComparator<DoubleValues,Double> {
     private double[] docValues;
     private final double[] values;
     private final double missingValue;
     private double bottom;
 
-
     DoubleComparator(int numHits, DoubleValuesCreator creator, Double missingValue ) {
       super( creator, missingValue != null );
       values = new double[numHits];
@@ -324,13 +331,13 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Double value(int slot) {
       return Double.valueOf(values[slot]);
     }
   }
 
   /** Uses float index values to sort by ascending value */
-  public static final class FloatDocValuesComparator extends FieldComparator {
+  public static final class FloatDocValuesComparator extends FieldComparator<Double> {
     private final double[] values;
     private Source currentReaderValues;
     private final String field;
@@ -386,14 +393,14 @@
     }
 
     @Override
-    public Comparable<Double> value(int slot) {
+    public Double value(int slot) {
       return Double.valueOf(values[slot]);
     }
   }
 
   /** Parses field's values as float (using {@link
    *  FieldCache#getFloats} and sorts by ascending value */
-  public static final class FloatComparator extends NumericComparator<FloatValues> {
+  public static final class FloatComparator extends NumericComparator<FloatValues,Float> {
     private float[] docValues;
     private final float[] values;
     private final float missingValue;
@@ -460,14 +467,14 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Float value(int slot) {
       return Float.valueOf(values[slot]);
     }
   }
 
   /** Parses field's values as short (using {@link
    *  FieldCache#getShorts} and sorts by ascending value */
-  public static final class ShortComparator extends NumericComparator<ShortValues> {
+  public static final class ShortComparator extends NumericComparator<ShortValues,Short> {
     private short[] docValues;
     private final short[] values;
     private short bottom;
@@ -516,14 +523,14 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Short value(int slot) {
       return Short.valueOf(values[slot]);
     }
   }
 
   /** Parses field's values as int (using {@link
    *  FieldCache#getInts} and sorts by ascending value */
-  public static final class IntComparator extends NumericComparator<IntValues> {
+  public static final class IntComparator extends NumericComparator<IntValues,Integer> {
     private int[] docValues;
     private final int[] values;
     private int bottom;                           // Value of bottom of queue
@@ -594,13 +601,13 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Integer value(int slot) {
       return Integer.valueOf(values[slot]);
     }
   }
 
   /** Loads int index values and sorts by ascending value. */
-  public static final class IntDocValuesComparator extends FieldComparator {
+  public static final class IntDocValuesComparator extends FieldComparator<Long> {
     private final long[] values;
     private Source currentReaderValues;
     private final String field;
@@ -660,14 +667,14 @@
     }
 
     @Override
-    public Comparable<Long> value(int slot) {
+    public Long value(int slot) {
       return Long.valueOf(values[slot]);
     }
   }
 
   /** Parses field's values as long (using {@link
    *  FieldCache#getLongs} and sorts by ascending value */
-  public static final class LongComparator extends NumericComparator<LongValues> {
+  public static final class LongComparator extends NumericComparator<LongValues,Long> {
     private long[] docValues;
     private final long[] values;
     private long bottom;
@@ -735,7 +742,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Long value(int slot) {
       return Long.valueOf(values[slot]);
     }
   }
@@ -746,7 +753,7 @@
    *  using {@link TopScoreDocCollector} directly (which {@link
    *  IndexSearcher#search} uses when no {@link Sort} is
    *  specified). */
-  public static final class RelevanceComparator extends FieldComparator {
+  public static final class RelevanceComparator extends FieldComparator<Float> {
     private final float[] scores;
     private float bottom;
     private Scorer scorer;
@@ -791,15 +798,25 @@
     }
     
     @Override
-    public Comparable<?> value(int slot) {
+    public Float value(int slot) {
       return Float.valueOf(scores[slot]);
     }
+
+    // Override because we sort reverse of natural Float order:
+    @Override
+    public int compareValues(Float first, Float second) {
+      if (first > second) {
+        return -1;
+      } else if (first < second) {
+        return 1;
+      } else {
+        return 0;
+      }
+    }
   }
 
-
-
   /** Sorts by ascending docID */
-  public static final class DocComparator extends FieldComparator {
+  public static final class DocComparator extends FieldComparator<Integer> {
     private final int[] docIDs;
     private int docBase;
     private int bottom;
@@ -840,7 +857,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Integer value(int slot) {
       return Integer.valueOf(docIDs[slot]);
     }
   }
@@ -854,7 +871,7 @@
    *  to large results, this comparator will be much faster
    *  than {@link TermValComparator}.  For very small
    *  result sets it may be slower. */
-  public static final class TermOrdValComparator extends FieldComparator {
+  public static final class TermOrdValComparator extends FieldComparator<BytesRef> {
     /** @lucene.internal */
     final int[] ords;
     /** @lucene.internal */
@@ -920,7 +937,7 @@
      * the underlying array access when looking up doc->ord
      * @lucene.internal
      */
-    abstract class PerSegmentComparator extends FieldComparator {
+    abstract class PerSegmentComparator extends FieldComparator<BytesRef> {
       
       @Override
       public FieldComparator setNextReader(AtomicReaderContext context) throws IOException {
@@ -938,7 +955,7 @@
       }
 
       @Override
-      public Comparable<?> value(int slot) {
+      public BytesRef value(int slot) {
         return TermOrdValComparator.this.value(slot);
       }
     }
@@ -1244,7 +1261,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public BytesRef value(int slot) {
       return values[slot];
     }
   }
@@ -1253,7 +1270,7 @@
    *  comparisons are done using BytesRef.compareTo, which is
    *  slow for medium to large result sets but possibly
    *  very fast for very small results sets. */
-  public static final class TermValComparator extends FieldComparator {
+  public static final class TermValComparator extends FieldComparator<BytesRef> {
 
     private BytesRef[] values;
     private DocTerms docTerms;
@@ -1316,7 +1333,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public BytesRef value(int slot) {
       return values[slot];
     }
   }
Index: lucene/src/java/org/apache/lucene/search/FieldDoc.java
--- lucene/src/java/org/apache/lucene/search/FieldDoc.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/FieldDoc.java	Fri Jun 10 19:38:21 2011 -0400
@@ -40,12 +40,13 @@
 
   /** Expert: The values which are used to sort the referenced document.
    * The order of these will match the original sort criteria given by a
-   * Sort object.  Each Object will be either an Integer, Float or String,
-   * depending on the type of values in the terms of the original field.
+   * Sort object.  Each Object will have been returned from
+   * the <code>value</code> method corresponding
+   * FieldComparator used to sort this field.
    * @see Sort
    * @see IndexSearcher#search(Query,Filter,int,Sort)
    */
-  public Comparable[] fields;
+  public Object[] fields;
 
   /** Expert: Creates one of these objects with empty sort information. */
   public FieldDoc (int doc, float score) {
@@ -53,7 +54,7 @@
   }
 
   /** Expert: Creates one of these objects with the given sort information. */
-  public FieldDoc (int doc, float score, Comparable[] fields) {
+  public FieldDoc (int doc, float score, Object[] fields) {
     super (doc, score);
     this.fields = fields;
   }
Index: lucene/src/java/org/apache/lucene/search/FieldValueHitQueue.java
--- lucene/src/java/org/apache/lucene/search/FieldValueHitQueue.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/FieldValueHitQueue.java	Fri Jun 10 19:38:21 2011 -0400
@@ -200,7 +200,7 @@
    */
   FieldDoc fillFields(final Entry entry) {
     final int n = comparators.length;
-    final Comparable<?>[] fields = new Comparable[n];
+    final Object[] fields = new Object[n];
     for (int i = 0; i < n; ++i) {
       fields[i] = comparators[i].value(entry.slot);
     }
Index: lucene/src/java/org/apache/lucene/search/IndexSearcher.java
--- lucene/src/java/org/apache/lucene/search/IndexSearcher.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/IndexSearcher.java	Fri Jun 10 19:38:21 2011 -0400
@@ -443,7 +443,7 @@
    * Collector)}.</p>
    */
   protected TopFieldDocs search(Weight weight, Filter filter, int nDocs,
-                             Sort sort, boolean fillFields)
+                                Sort sort, boolean fillFields)
       throws IOException {
 
     if (sort == null) throw new NullPointerException();
Index: lucene/src/java/org/apache/lucene/search/SortField.java
--- lucene/src/java/org/apache/lucene/search/SortField.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/SortField.java	Fri Jun 10 19:38:21 2011 -0400
@@ -91,10 +91,10 @@
   public static final int BYTES = 12;
   
   /** Represents sorting by document score (relevance). */
-  public static final SortField FIELD_SCORE = new SortField (null, SCORE);
+  public static final SortField FIELD_SCORE = new SortField(null, SCORE);
 
   /** Represents sorting by document number (index order). */
-  public static final SortField FIELD_DOC = new SortField (null, DOC);
+  public static final SortField FIELD_DOC = new SortField(null, DOC);
 
   private String field;
   private int type;  // defaults to determining type dynamically
@@ -111,7 +111,7 @@
    *               <code>type</code> is SCORE or DOC.
    * @param type   Type of values in the terms.
    */
-  public SortField (String field, int type) {
+  public SortField(String field, int type) {
     initFieldType(field, type);
   }
 
@@ -122,7 +122,7 @@
    * @param type   Type of values in the terms.
    * @param reverse True if natural order should be reversed.
    */
-  public SortField (String field, int type, boolean reverse) {
+  public SortField(String field, int type, boolean reverse) {
     initFieldType(field, type);
     this.reverse = reverse;
   }
@@ -140,7 +140,7 @@
    *  @deprecated (4.0) use EntryCreator version
    */
   @Deprecated
-  public SortField (String field, FieldCache.Parser parser) {
+  public SortField(String field, FieldCache.Parser parser) {
     this(field, parser, false);
   }
 
@@ -158,7 +158,7 @@
    *  @deprecated (4.0) use EntryCreator version
    */
   @Deprecated
-  public SortField (String field, FieldCache.Parser parser, boolean reverse) {
+  public SortField(String field, FieldCache.Parser parser, boolean reverse) {
     if (field == null) {
       throw new IllegalArgumentException("field can only be null when type is SCORE or DOC");
     } 
@@ -225,7 +225,7 @@
    * @param field Name of field to sort by; cannot be <code>null</code>.
    * @param comparator Returns a comparator for sorting hits.
    */
-  public SortField (String field, FieldComparatorSource comparator) {
+  public SortField(String field, FieldComparatorSource comparator) {
     initFieldType(field, CUSTOM);
     this.comparatorSource = comparator;
   }
@@ -235,7 +235,7 @@
    * @param comparator Returns a comparator for sorting hits.
    * @param reverse True if natural order should be reversed.
    */
-  public SortField (String field, FieldComparatorSource comparator, boolean reverse) {
+  public SortField(String field, FieldComparatorSource comparator, boolean reverse) {
     initFieldType(field, CUSTOM);
     this.reverse = reverse;
     this.comparatorSource = comparator;
Index: lucene/src/java/org/apache/lucene/search/TopDocs.java
--- lucene/src/java/org/apache/lucene/search/TopDocs.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/java/org/apache/lucene/search/TopDocs.java	Fri Jun 10 19:38:21 2011 -0400
@@ -17,6 +17,10 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
+
+import org.apache.lucene.util.PriorityQueue;
+
 /** Represents hits returned by {@link
  * IndexSearcher#search(Query,Filter,int)} and {@link
  * IndexSearcher#search(Query,int)}. */
@@ -52,4 +56,212 @@
     this.scoreDocs = scoreDocs;
     this.maxScore = maxScore;
   }
+
+  // Refers to one hit:
+  private static class ShardRef {
+    // Which shard (index into shardHits[]):
+    final int shardIndex;
+
+    // Which hit within the shard:
+    int hitIndex;
+
+    public ShardRef(int shardIndex) {
+      this.shardIndex = shardIndex;
+    }
+
+    @Override
+    public String toString() {
+      return "ShardRef(shardIndex=" + shardIndex + " hitIndex=" + hitIndex + ")";
+    }
+  };
+
+  // Specialized MergeSortQueue that just merges by
+  // relevance score, descending:
+  private static class ScoreMergeSortQueue extends PriorityQueue<ShardRef> {
+    final ScoreDoc[][] shardHits;
+
+    public ScoreMergeSortQueue(TopDocs[] shardHits) {
+      super(shardHits.length);
+      this.shardHits = new ScoreDoc[shardHits.length][];
+      for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
+        this.shardHits[shardIDX] = shardHits[shardIDX].scoreDocs;
+      }
+    }
+
+    // Returns true if first is < second
+    public boolean lessThan(ShardRef first, ShardRef second) {
+      assert first != second;
+      final float firstScore = shardHits[first.shardIndex][first.hitIndex].score;
+      final float secondScore = shardHits[second.shardIndex][second.hitIndex].score;
+
+      if (firstScore < secondScore) {
+        return false;
+      } else if (firstScore > secondScore) {
+        return true;
+      } else {
+        // Tie break: earlier shard wins
+        if (first.shardIndex < second.shardIndex) {
+          return true;
+        } else if (first.shardIndex > second.shardIndex) {
+          return false;
+        } else {
+          // Tie break in same shard: resolve however the
+          // shard had resolved it:
+          assert first.hitIndex != second.hitIndex;
+          return first.hitIndex < second.hitIndex;
+        }
+      }
+    }
+  }
+
+  private static class MergeSortQueue extends PriorityQueue<ShardRef> {
+    // These are really FieldDoc instances:
+    final ScoreDoc[][] shardHits;
+    final FieldComparator[] comparators;
+    final int[] reverseMul;
+
+    public MergeSortQueue(Sort sort, TopDocs[] shardHits) throws IOException {
+      super(shardHits.length);
+      this.shardHits = new ScoreDoc[shardHits.length][];
+      for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
+        final ScoreDoc[] shard = shardHits[shardIDX].scoreDocs;
+        //System.out.println("  init shardIdx=" + shardIDX + " hits=" + shard);
+        if (shard != null) {
+          this.shardHits[shardIDX] = shard;
+          // Fail gracefully if API is misused:
+          for(int hitIDX=0;hitIDX<shard.length;hitIDX++) {
+            final ScoreDoc sd = shard[hitIDX];
+            if (!(sd instanceof FieldDoc)) {
+              throw new IllegalArgumentException("shard " + shardIDX + " was not sorted by the provided Sort (expected FieldDoc but got ScoreDoc)");
+            }
+            final FieldDoc fd = (FieldDoc) sd;
+            if (fd.fields == null) {
+              throw new IllegalArgumentException("shard " + shardIDX + " did not set sort field values (FieldDoc.fields is null); you must pass fillFields=true to IndexSearcher.search on each shard");
+            }
+          }
+        }
+      }
+
+      final SortField[] sortFields = sort.getSort();
+      comparators = new FieldComparator[sortFields.length];
+      reverseMul = new int[sortFields.length];
+      for(int compIDX=0;compIDX<sortFields.length;compIDX++) {
+        final SortField sortField = sortFields[compIDX];
+        comparators[compIDX] = sortField.getComparator(1, compIDX);
+        reverseMul[compIDX] = sortField.getReverse() ? -1 : 1;
+      }
+    }
+
+    // Returns true if first is < second
+    @SuppressWarnings("unchecked")
+    public boolean lessThan(ShardRef first, ShardRef second) {
+      assert first != second;
+      final FieldDoc firstFD = (FieldDoc) shardHits[first.shardIndex][first.hitIndex];
+      final FieldDoc secondFD = (FieldDoc) shardHits[second.shardIndex][second.hitIndex];
+      //System.out.println("  lessThan:\n     first=" + first + " doc=" + firstFD.doc + " score=" + firstFD.score + "\n    second=" + second + " doc=" + secondFD.doc + " score=" + secondFD.score);
+
+      for(int compIDX=0;compIDX<comparators.length;compIDX++) {
+        final FieldComparator comp = comparators[compIDX];
+        //System.out.println("    cmp idx=" + compIDX + " cmp1=" + firstFD.fields[compIDX] + " cmp2=" + secondFD.fields[compIDX] + " reverse=" + reverseMul[compIDX]);
+
+        final int cmp = reverseMul[compIDX] * comp.compareValues(firstFD.fields[compIDX], secondFD.fields[compIDX]);
+        
+        if (cmp != 0) {
+          //System.out.println("    return " + (cmp < 0));
+          return cmp < 0;
+        }
+      }
+
+      // Tie break: earlier shard wins
+      if (first.shardIndex < second.shardIndex) {
+        //System.out.println("    return tb true");
+        return true;
+      } else if (first.shardIndex > second.shardIndex) {
+        //System.out.println("    return tb false");
+        return false;
+      } else {
+        // Tie break in same shard: resolve however the
+        // shard had resolved it:
+        //System.out.println("    return tb " + (first.hitIndex < second.hitIndex));
+        assert first.hitIndex != second.hitIndex;
+        return first.hitIndex < second.hitIndex;
+      }
+    }
+  }
+
+  /** Returned from {@link #merge}, to include the merged
+   *  TopDocs as well as the reference to which original
+   *  TopDocs shard each hit came from.
+   *
+   * @lucene.experimental */
+  public static class TopDocsAndShards {
+
+    /** Merged hits from all shards */
+    public final TopDocs hits;
+
+    /** Parallel array matching <code>hits.scoreDocs</code> */
+    public final int[] shardIndex;
+
+    public TopDocsAndShards(TopDocs hits, int[] shardIndex) {
+      this.hits = hits;
+      this.shardIndex = shardIndex;
+    }
+  }
+
+  /** Returns a new TopDocs, containing topN results across
+   *  the provided TopDocs, sorting by the specified {@link
+   *  Sort}.  Each of the TopDocs must have been sorted by
+   *  the same Sort, and sort field values must have been
+   *  filled (ie, <code>fillFields=true</code> must be
+   *  passed to {@link
+   *  TopFieldCollector#create}.
+   *
+   * <p>Pass sort=null to merge sort by score descending.
+   *
+   * @lucene.experimental */
+  public static TopDocsAndShards merge(Sort sort, int topN, TopDocs[] shardHits) throws IOException {
+
+    final PriorityQueue<ShardRef> queue;
+    if (sort == null) {
+      queue = new ScoreMergeSortQueue(shardHits);
+    } else {
+      queue = new MergeSortQueue(sort, shardHits);
+    }
+
+    int totalHitCount = 0;
+    float maxScore = Float.MIN_VALUE;
+    for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
+      final TopDocs shard = shardHits[shardIDX];
+      if (shard.scoreDocs != null && shard.scoreDocs.length > 0) {
+        totalHitCount += shard.totalHits;
+        queue.add(new ShardRef(shardIDX));
+        maxScore = Math.max(maxScore, shard.getMaxScore());
+        //System.out.println("  maxScore now " + maxScore + " vs " + shard.getMaxScore());
+      }
+    }
+
+    final ScoreDoc[] hits = new ScoreDoc[Math.min(topN, totalHitCount)];
+    final int[] shardIndex = new int[hits.length];
+
+    int hitUpto = 0;
+    while(hitUpto < hits.length) {
+      assert queue.size() > 0;
+      ShardRef ref = queue.pop();
+      hits[hitUpto] = shardHits[ref.shardIndex].scoreDocs[ref.hitIndex++];
+      shardIndex[hitUpto] = ref.shardIndex;
+
+      //System.out.println("  hitUpto=" + hitUpto);
+      //System.out.println("    doc=" + hits[hitUpto].doc + " score=" + hits[hitUpto].score);
+
+      hitUpto++;
+
+      if (ref.hitIndex < shardHits[ref.shardIndex].scoreDocs.length) {
+        // Not done with this these TopDocs yet:
+        queue.add(ref);
+      }
+    }
+
+    return new TopDocsAndShards(new TopDocs(totalHitCount, hits, maxScore),
+                                shardIndex);
+  }
 }
Index: lucene/src/test-framework/org/apache/lucene/index/RandomIndexWriter.java
--- lucene/src/test-framework/org/apache/lucene/index/RandomIndexWriter.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test-framework/org/apache/lucene/index/RandomIndexWriter.java	Fri Jun 10 19:38:21 2011 -0400
@@ -308,16 +308,24 @@
     return getReader(true);
   }
 
+  private boolean doRandomOptimize = true;
+
+  public void setDoRandomOptimize(boolean v) {
+    doRandomOptimize = v;
+  }
+
   private void doRandomOptimize() throws IOException {
-    final int segCount = w.getSegmentCount();
-    if (r.nextBoolean() || segCount == 0) {
-      // full optimize
-      w.optimize();
-    } else {
-      // partial optimize
-      final int limit = _TestUtil.nextInt(r, 1, segCount);
-      w.optimize(limit);
-      assert w.getSegmentCount() <= limit: "limit=" + limit + " actual=" + w.getSegmentCount();
+    if (doRandomOptimize) {
+      final int segCount = w.getSegmentCount();
+      if (r.nextBoolean() || segCount == 0) {
+        // full optimize
+        w.optimize();
+      } else {
+        // partial optimize
+        final int limit = _TestUtil.nextInt(r, 1, segCount);
+        w.optimize(limit);
+        assert w.getSegmentCount() <= limit: "limit=" + limit + " actual=" + w.getSegmentCount();
+      }
     }
     switchDoDocValues();
   }
Index: lucene/src/test-framework/org/apache/lucene/util/LuceneTestCase.java
--- lucene/src/test-framework/org/apache/lucene/util/LuceneTestCase.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test-framework/org/apache/lucene/util/LuceneTestCase.java	Fri Jun 10 19:38:21 2011 -0400
@@ -1484,4 +1484,5 @@
 
   @Ignore("just a hack")
   public final void alwaysIgnoredTestMethod() {}
-}
+
+}
\ No newline at end of file
Index: lucene/src/test-framework/org/apache/lucene/util/_TestUtil.java
--- lucene/src/test-framework/org/apache/lucene/util/_TestUtil.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test-framework/org/apache/lucene/util/_TestUtil.java	Fri Jun 10 19:38:21 2011 -0400
@@ -27,10 +27,10 @@
 import java.io.PrintStream;
 import java.lang.reflect.Method;
 import java.util.Enumeration;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Random;
-import java.util.Map;
-import java.util.HashMap;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
@@ -46,6 +46,9 @@
 import org.apache.lucene.index.TieredMergePolicy;
 import org.apache.lucene.index.codecs.Codec;
 import org.apache.lucene.index.codecs.CodecProvider;
+import org.apache.lucene.search.FieldDoc;
+import org.apache.lucene.search.ScoreDoc;
+import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.store.Directory;
 import org.junit.Assert;
 
@@ -467,4 +470,24 @@
     newName.append(suffix);
     return new File(directory, newName.toString());
   }
+
+  public static void assertEquals(TopDocs expected, TopDocs actual) {
+    Assert.assertEquals("wrong total hits", expected.totalHits, actual.totalHits);
+    Assert.assertEquals("wrong maxScore", expected.getMaxScore(), actual.getMaxScore(), 0.0);
+    Assert.assertEquals("wrong hit count", expected.scoreDocs.length, actual.scoreDocs.length);
+    for(int hitIDX=0;hitIDX<expected.scoreDocs.length;hitIDX++) {
+      final ScoreDoc expectedSD = expected.scoreDocs[hitIDX];
+      final ScoreDoc actualSD = actual.scoreDocs[hitIDX];
+      Assert.assertEquals("wrong hit docID", expectedSD.doc, actualSD.doc);
+      Assert.assertEquals("wrong hit score", expectedSD.score, actualSD.score, 0.0);
+      if (expectedSD instanceof FieldDoc) {
+        Assert.assertTrue(actualSD instanceof FieldDoc);
+        Assert.assertEquals("wrong sort field values",
+                            ((FieldDoc) expectedSD).fields,
+                            ((FieldDoc) actualSD).fields);
+      } else {
+        Assert.assertFalse(actualSD instanceof FieldDoc);
+      }
+    }
+  }
 }
Index: lucene/src/test/org/apache/lucene/search/JustCompileSearch.java
--- lucene/src/test/org/apache/lucene/search/JustCompileSearch.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test/org/apache/lucene/search/JustCompileSearch.java	Fri Jun 10 19:38:21 2011 -0400
@@ -103,7 +103,7 @@
     
   }
 
-  static final class JustCompileFieldComparator extends FieldComparator {
+  static final class JustCompileFieldComparator extends FieldComparator<Object> {
 
     @Override
     public int compare(int slot1, int slot2) {
@@ -132,10 +132,10 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Object value(int slot) {
       throw new UnsupportedOperationException(UNSUPPORTED_MSG);
     }
-    
+
   }
 
   static final class JustCompileFieldComparatorSource extends FieldComparatorSource {
Index: lucene/src/test/org/apache/lucene/search/TestElevationComparator.java
--- lucene/src/test/org/apache/lucene/search/TestElevationComparator.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test/org/apache/lucene/search/TestElevationComparator.java	Fri Jun 10 19:38:21 2011 -0400
@@ -139,7 +139,7 @@
 
   @Override
   public FieldComparator newComparator(final String fieldname, final int numHits, int sortPos, boolean reversed) throws IOException {
-   return new FieldComparator() {
+   return new FieldComparator<Integer>() {
 
      FieldCache.DocTermsIndex idIndex;
      private final int[] values = new int[numHits];
@@ -184,7 +184,7 @@
      }
 
      @Override
-     public Comparable<?> value(int slot) {
+     public Integer value(int slot) {
        return Integer.valueOf(values[slot]);
      }
    };
Index: lucene/src/test/org/apache/lucene/search/TestSort.java
--- lucene/src/test/org/apache/lucene/search/TestSort.java	Fri Jun 10 16:56:32 2011 -0400
+++ lucene/src/test/org/apache/lucene/search/TestSort.java	Fri Jun 10 19:38:21 2011 -0400
@@ -511,7 +511,7 @@
     assertMatches (empty, queryX, sort, "");
   }
 
-  static class MyFieldComparator extends FieldComparator {
+  static class MyFieldComparator extends FieldComparator<Integer> {
     int[] docValues;
     int[] slotValues;
     int bottomValue;
@@ -527,6 +527,7 @@
 
     @Override
     public int compare(int slot1, int slot2) {
+      // values are small enough that overflow won't happen
       return slotValues[slot1] - slotValues[slot2];
     }
 
@@ -553,7 +554,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public Integer value(int slot) {
       return Integer.valueOf(slotValues[slot]);
     }
   }
Index: lucene/src/test/org/apache/lucene/search/TestTopDocsMerge.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ lucene/src/test/org/apache/lucene/search/TestTopDocsMerge.java	Fri Jun 10 19:38:21 2011 -0400
@@ -0,0 +1,225 @@
+package org.apache.lucene.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.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.Field;
+import org.apache.lucene.document.NumericField;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.RandomIndexWriter;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.LuceneTestCase;
+import org.apache.lucene.util._TestUtil;
+
+public class TestTopDocsMerge extends LuceneTestCase {
+
+  private static class ShardSearcher extends IndexSearcher {
+    private final IndexReader.AtomicReaderContext[] ctx;
+
+    public ShardSearcher(IndexReader.AtomicReaderContext ctx) {
+      super(ctx.parent);
+      this.ctx = new IndexReader.AtomicReaderContext[] {ctx};
+    }
+
+    public void search(Weight weight, Collector collector) throws IOException {
+      search(ctx, weight, null, collector);
+    }
+
+    public TopDocs search(Weight weight, int topN) throws IOException {
+      return search(ctx, weight, null, topN);
+    }
+  }
+
+  public void testSort() throws Exception {
+
+    IndexReader reader = null;
+    IndexReader[] subReaders = null;
+    Directory dir = null;
+
+    final int numDocs = atLeast(1000);
+    //final int numDocs = atLeast(50);
+
+    final String[] tokens = new String[] {"a", "b", "c", "d", "e"};
+
+    if (VERBOSE) {
+      System.out.println("TEST: make index");
+    }
+
+    // Iterate until we get an index with more than one segment:
+    while(true) {
+
+      dir = newDirectory();
+      final RandomIndexWriter w = new RandomIndexWriter(random, dir);
+      w.setDoRandomOptimize(false);
+
+      w.w.getConfig().setMaxBufferedDocs(atLeast(100));
+
+      final String[] content = new String[atLeast(20)];
+
+      for(int contentIDX=0;contentIDX<content.length;contentIDX++) {
+        final StringBuilder sb = new StringBuilder();
+        final int numTokens = _TestUtil.nextInt(random, 1, 10);
+        for(int tokenIDX=0;tokenIDX<numTokens;tokenIDX++) {
+          sb.append(tokens[random.nextInt(tokens.length)]).append(' ');
+        }
+        content[contentIDX] = sb.toString();
+      }
+
+      for(int docIDX=0;docIDX<numDocs;docIDX++) {
+        final Document doc = new Document();
+        doc.add(newField("string", _TestUtil.randomRealisticUnicodeString(random), Field.Index.NOT_ANALYZED));
+        doc.add(newField("text", content[random.nextInt(content.length)], Field.Index.ANALYZED));
+        doc.add(new NumericField("float").setFloatValue(random.nextFloat()));
+        final int intValue;
+        if (random.nextInt(100) == 17) {
+          intValue = Integer.MIN_VALUE;
+        } else if (random.nextInt(100) == 17) {
+          intValue = Integer.MAX_VALUE;
+        } else {
+          intValue = random.nextInt();
+        }
+        doc.add(new NumericField("int").setIntValue(intValue));
+        if (VERBOSE) {
+          System.out.println("  doc=" + doc);
+        }
+        w.addDocument(doc);
+      }
+
+      reader = w.getReader();
+      subReaders = reader.getSequentialSubReaders();
+      if (VERBOSE) {
+        System.out.println("TEST: got " + subReaders.length + " subs; reader=" + reader);
+      }
+      w.close();
+      if (subReaders.length > 1) {
+        break;
+      }
+      reader.close();
+      dir.close();
+
+      // Try again...
+      if (VERBOSE) {
+        System.out.println("TEST: build index again");
+      }
+    }
+
+    final IndexSearcher searcher = new IndexSearcher(reader);
+    final ShardSearcher[] subSearchers = new ShardSearcher[subReaders.length];
+    final IndexReader.ReaderContext ctx = reader.getTopReaderContext();
+
+    for(int searcherIDX=0;searcherIDX<subSearchers.length;searcherIDX++) { 
+      subSearchers[searcherIDX] = new ShardSearcher(((IndexReader.CompositeReaderContext) ctx).leaves[searcherIDX]);
+    }
+
+    final List<SortField> sortFields = new ArrayList<SortField>();
+    sortFields.add(new SortField("string", SortField.STRING, true));
+    sortFields.add(new SortField("string", SortField.STRING, false));
+    sortFields.add(new SortField("int", SortField.INT, true));
+    sortFields.add(new SortField("int", SortField.INT, false));
+    sortFields.add(new SortField("float", SortField.FLOAT, true));
+    sortFields.add(new SortField("float", SortField.FLOAT, false));
+    sortFields.add(new SortField(null, SortField.SCORE, true));
+    sortFields.add(new SortField(null, SortField.SCORE, false));
+    sortFields.add(new SortField(null, SortField.DOC, true));
+    sortFields.add(new SortField(null, SortField.DOC, false));
+
+    for(int iter=0;iter<1000*RANDOM_MULTIPLIER;iter++) {
+
+      // TODO: custom FieldComp...
+      final Query query = new TermQuery(new Term("text", tokens[random.nextInt(tokens.length)]));
+
+      final Sort sort;
+      if (random.nextInt(10) == 4) {
+        // Sort by score
+        sort = null;
+      } else {
+        final SortField[] randomSortFields = new SortField[_TestUtil.nextInt(random, 1, 3)];
+        for(int sortIDX=0;sortIDX<randomSortFields.length;sortIDX++) {
+          randomSortFields[sortIDX] = sortFields.get(random.nextInt(sortFields.size()));
+        }
+        sort = new Sort(randomSortFields);
+      }
+
+      final int numHits = _TestUtil.nextInt(random, 1, numDocs+5);
+      //final int numHits = 5;
+      
+      if (VERBOSE) {
+        System.out.println("TEST: search query=" + query + " sort=" + sort + " numHits=" + numHits);
+      }
+
+      // First search on whole index:
+      final TopDocs topHits;
+      if (sort == null) {
+        topHits = searcher.search(query, numHits);
+      } else {
+        final TopFieldCollector c = TopFieldCollector.create(sort, numHits, true, true, true, random.nextBoolean());
+        searcher.search(query, c);
+        topHits = c.topDocs(0, numHits);
+      }
+
+      if (VERBOSE) {
+        System.out.println("  top search: " + topHits.totalHits + " totalHits; hits=" + (topHits.scoreDocs == null ? "null" : topHits.scoreDocs.length));
+        if (topHits.scoreDocs != null) {
+          for(int hitIDX=0;hitIDX<topHits.scoreDocs.length;hitIDX++) {
+            final ScoreDoc sd = topHits.scoreDocs[hitIDX];
+            System.out.println("    doc=" + sd.doc + " score=" + sd.score);
+          }
+        }
+      }
+
+      // ... then all shards:
+      final Weight w = query.weight(searcher);
+
+      final TopDocs[] shardHits = new TopDocs[subSearchers.length];
+      for(int shardIDX=0;shardIDX<subSearchers.length;shardIDX++) {
+        final TopDocs subHits;
+        final ShardSearcher subSearcher = subSearchers[shardIDX];
+        if (sort == null) {
+          subHits = subSearcher.search(w, numHits);
+        } else {
+          final TopFieldCollector c = TopFieldCollector.create(sort, numHits, true, true, true, random.nextBoolean());
+          subSearcher.search(w, c);
+          subHits = c.topDocs(0, numHits);
+        }
+
+        shardHits[shardIDX] = subHits;
+        if (VERBOSE) {
+          System.out.println("  shard=" + shardIDX + " " + subHits.totalHits + " totalHits hits=" + (subHits.scoreDocs == null ? "null" : subHits.scoreDocs.length));
+          if (subHits.scoreDocs != null) {
+            for(ScoreDoc sd : subHits.scoreDocs) {
+              System.out.println("    doc=" + sd.doc + " score=" + sd.score);
+            }
+          }
+        }
+      }
+
+      // Merge:
+      final TopDocs mergedHits = TopDocs.merge(sort, numHits, shardHits).hits;
+
+      _TestUtil.assertEquals(topHits, mergedHits);
+    }
+        
+    reader.close();
+    dir.close();
+  }
+}
\ No newline at end of file
Index: modules/grouping/src/java/org/apache/lucene/search/grouping/BlockGroupingCollector.java
--- modules/grouping/src/java/org/apache/lucene/search/grouping/BlockGroupingCollector.java	Fri Jun 10 16:56:32 2011 -0400
+++ modules/grouping/src/java/org/apache/lucene/search/grouping/BlockGroupingCollector.java	Fri Jun 10 19:38:21 2011 -0400
@@ -348,7 +348,7 @@
       }
       totalGroupedHitCount += og.count;
 
-      final Comparable[] groupSortValues;
+      final Object[] groupSortValues;
 
       if (fillSortFields) {
         groupSortValues = new Comparable[comparators.length];
Index: modules/grouping/src/java/org/apache/lucene/search/grouping/GroupDocs.java
--- modules/grouping/src/java/org/apache/lucene/search/grouping/GroupDocs.java	Fri Jun 10 16:56:32 2011 -0400
+++ modules/grouping/src/java/org/apache/lucene/search/grouping/GroupDocs.java	Fri Jun 10 19:38:21 2011 -0400
@@ -40,13 +40,13 @@
 
   /** Matches the groupSort passed to {@link
    *  AbstractFirstPassGroupingCollector}. */
-  public final Comparable[] groupSortValues;
+  public final Object[] groupSortValues;
 
   public GroupDocs(float maxScore,
                    int totalHits,
                    ScoreDoc[] scoreDocs,
                    GROUP_VALUE_TYPE groupValue,
-                   Comparable[] groupSortValues) {
+                   Object[] groupSortValues) {
     this.maxScore = maxScore;
     this.totalHits = totalHits;
     this.scoreDocs = scoreDocs;
Index: modules/grouping/src/java/org/apache/lucene/search/grouping/SearchGroup.java
--- modules/grouping/src/java/org/apache/lucene/search/grouping/SearchGroup.java	Fri Jun 10 16:56:32 2011 -0400
+++ modules/grouping/src/java/org/apache/lucene/search/grouping/SearchGroup.java	Fri Jun 10 19:38:21 2011 -0400
@@ -28,5 +28,5 @@
   public GROUP_VALUE_TYPE groupValue;
 
   /** The sort values used during sorting. Can be <code>null</code>. */
-  public Comparable[] sortValues;
+  public Object[] sortValues;
 }
Index: solr/src/java/org/apache/solr/handler/component/QueryElevationComponent.java
--- solr/src/java/org/apache/solr/handler/component/QueryElevationComponent.java	Fri Jun 10 16:56:32 2011 -0400
+++ solr/src/java/org/apache/solr/handler/component/QueryElevationComponent.java	Fri Jun 10 19:38:21 2011 -0400
@@ -476,8 +476,8 @@
   }
 
   @Override
-  public FieldComparator newComparator(final String fieldname, final int numHits, int sortPos, boolean reversed) throws IOException {
-    return new FieldComparator() {
+  public FieldComparator<Integer> newComparator(final String fieldname, final int numHits, int sortPos, boolean reversed) throws IOException {
+    return new FieldComparator<Integer>() {
       
       FieldCache.DocTermsIndex idIndex;
       private final int[] values = new int[numHits];
@@ -517,7 +517,7 @@
       }
 
       @Override
-      public Comparable value(int slot) {
+      public Integer value(int slot) {
         return values[slot];
       }
     };
Index: solr/src/java/org/apache/solr/schema/RandomSortField.java
--- solr/src/java/org/apache/solr/schema/RandomSortField.java	Fri Jun 10 16:56:32 2011 -0400
+++ solr/src/java/org/apache/solr/schema/RandomSortField.java	Fri Jun 10 19:38:21 2011 -0400
@@ -102,8 +102,8 @@
 
   private static FieldComparatorSource randomComparatorSource = new FieldComparatorSource() {
     @Override
-    public FieldComparator newComparator(final String fieldname, final int numHits, int sortPos, boolean reversed) throws IOException {
-      return new FieldComparator() {
+    public FieldComparator<Integer> newComparator(final String fieldname, final int numHits, int sortPos, boolean reversed) throws IOException {
+      return new FieldComparator<Integer>() {
         int seed;
         private final int[] values = new int[numHits];
         int bottomVal;
@@ -135,7 +135,7 @@
         }
 
         @Override
-        public Comparable value(int slot) {
+        public Integer value(int slot) {
           return values[slot];
         }
       };
Index: solr/src/java/org/apache/solr/search/MissingStringLastComparatorSource.java
--- solr/src/java/org/apache/solr/search/MissingStringLastComparatorSource.java	Fri Jun 10 16:56:32 2011 -0400
+++ solr/src/java/org/apache/solr/search/MissingStringLastComparatorSource.java	Fri Jun 10 19:38:21 2011 -0400
@@ -56,7 +56,7 @@
 
 // Copied from Lucene's TermOrdValComparator and modified since the Lucene version couldn't
 // be extended.
-class TermOrdValComparator_SML extends FieldComparator {
+class TermOrdValComparator_SML extends FieldComparator<BytesRef> {
   private static final int NULL_ORD = Integer.MAX_VALUE;
 
   private final int[] ords;
@@ -98,7 +98,7 @@
   }
 
   @Override
-  public Comparable<?> value(int slot) {
+  public BytesRef value(int slot) {
     throw new UnsupportedOperationException();
   }
 
@@ -111,7 +111,7 @@
   // ords) per-segment comparator.  NOTE: this is messy;
   // we do this only because hotspot can't reliably inline
   // the underlying array access when looking up doc->ord
-  private static abstract class PerSegmentComparator extends FieldComparator {
+  private static abstract class PerSegmentComparator extends FieldComparator<BytesRef> {
     protected TermOrdValComparator_SML parent;
     protected final int[] ords;
     protected final BytesRef[] values;
@@ -199,7 +199,7 @@
     }
 
     @Override
-    public Comparable<?> value(int slot) {
+    public BytesRef value(int slot) {
       return values==null ? parent.NULL_VAL : values[slot];
     }
   }
Index: solr/src/java/org/apache/solr/search/function/ValueSource.java
--- solr/src/java/org/apache/solr/search/function/ValueSource.java	Fri Jun 10 16:56:32 2011 -0400
+++ solr/src/java/org/apache/solr/search/function/ValueSource.java	Fri Jun 10 19:38:21 2011 -0400
@@ -141,7 +141,7 @@
    * off of the {@link org.apache.solr.search.function.DocValues} for a ValueSource
    * instead of the normal Lucene FieldComparator that works off of a FieldCache.
    */
-  class ValueSourceComparator extends FieldComparator {
+  class ValueSourceComparator extends FieldComparator<Double> {
     private final double[] values;
     private DocValues docVals;
     private double bottom;
@@ -195,7 +195,7 @@
     }
 
     @Override
-    public Comparable value(int slot) {
+    public Double value(int slot) {
       return values[slot];
     }
   }