LUCENE-5441: Decouple (Sparse)FixedBitSet from DocIdSet.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1633628 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/search/DocValuesDocIdSet.java

@@ -19,6 +19,7 @@ package org.apache.lucene.search;
 import java.io.IOException;
 
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -116,7 +117,7 @@ public abstract class DocValuesDocIdSet extends DocIdSet {
     } else if (acceptDocs instanceof FixedBitSet) {
       // special case for FixedBitSet: use the iterator and filter it
       // (used e.g. when Filters are chained by FilteredQuery)
-      return new FilteredDocIdSetIterator(((DocIdSet) acceptDocs).iterator()) {
+      return new FilteredDocIdSetIterator(new FixedBitDocIdSet((FixedBitSet) acceptDocs).iterator()) {
         @Override
         protected boolean match(int doc) {
           return DocValuesDocIdSet.this.matchDoc(doc);

lucene/core/src/java/org/apache/lucene/search/SloppyPhraseScorer.java

@@ -510,9 +510,8 @@ final class SloppyPhraseScorer extends Scorer {
     HashMap<Term,Integer> tg = new HashMap<>();
     Term[] t = tord.keySet().toArray(new Term[0]);
     for (int i=0; i<bb.size(); i++) { // i is the group no.
-      DocIdSetIterator bits = bb.get(i).iterator();
+      FixedBitSet bits = bb.get(i);
-      int ord;
+      for (int ord = bits.nextSetBit(0); ord != -1; ord = ord + 1 >= bits.length() ? -1 : bits.nextSetBit(ord + 1)) {
-      while ((ord=bits.nextDoc())!=NO_MORE_DOCS) {
         tg.put(t[ord],i);
       }
     }

lucene/core/src/java/org/apache/lucene/util/DocIdSetBuilder.java

@@ -21,6 +21,7 @@ import java.io.IOException;
 
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.util.SparseFixedBitSet.SparseFixedBitSetIterator;
 
 /**
  * A builder of {@link DocIdSet}s that supports random access.
@@ -63,7 +64,7 @@ public final class DocIdSetBuilder {
         denseSet = new FixedBitSet(maxDoc);
         denseSet.or(it);
         if (sparseSet != null) {
-          denseSet.or(sparseSet.iterator());
+          denseSet.or(new SparseFixedBitSetIterator(sparseSet, 0L));
         }
         return;
       }
@@ -84,7 +85,14 @@ public final class DocIdSetBuilder {
    * anymore after this method has been called.
    */
   public DocIdSet build() {
-    final DocIdSet result = denseSet != null ? denseSet : sparseSet;
+    final DocIdSet result;
+    if (denseSet != null) {
+      result = new FixedBitDocIdSet(denseSet, denseSet.cardinality());
+    } else if (sparseSet != null) {
+      result = new SparseFixedBitDocIdSet(sparseSet, sparseSet.approximateCardinality());
+    } else {
+      result = null;
+    }
     denseSet = null;
     sparseSet = null;
     costUpperBound = 0;

lucene/core/src/java/org/apache/lucene/util/FixedBitDocIdSet.java

@@ -0,0 +1,79 @@
+package org.apache.lucene.util;
+
+/*
+ * 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 org.apache.lucene.search.DocIdSet;
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
+
+/**
+ * Implementation of the {@link DocIdSet} interface on top of a {@link FixedBitSet}.
+ * @lucene.internal
+ */
+public class FixedBitDocIdSet extends DocIdSet {
+
+  private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(SparseFixedBitDocIdSet.class);
+
+  private final FixedBitSet set;
+  private final long cost;
+
+  /**
+   * Wrap the given {@link FixedBitSet} as a {@link DocIdSet}. The provided
+   * {@link FixedBitSet} should not be modified after having wrapped as a
+   * {@link DocIdSet}.
+   */
+  public FixedBitDocIdSet(FixedBitSet set, long cost) {
+    this.set = set;
+    this.cost = cost;
+  }
+
+  /**
+   * Same as {@link #FixedBitDocIdSet(FixedBitSet, long)} but uses the set
+   * {@link FixedBitSet#cardinality() cardinality} as a cost.
+   */
+  public FixedBitDocIdSet(FixedBitSet set) {
+    this(set, set.cardinality());
+  }
+
+  @Override
+  public DocIdSetIterator iterator() {
+    return new FixedBitSetIterator(set, cost);
+  }
+
+  @Override
+  public FixedBitSet bits() {
+    return set;
+  }
+
+  /** This DocIdSet implementation is cacheable. */
+  @Override
+  public boolean isCacheable() {
+    return true;
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    return BASE_RAM_BYTES_USED + set.ramBytesUsed();
+  }
+
+  @Override
+  public String toString() {
+    return getClass().getSimpleName() + "(set=" + set + ",cost=" + cost + ")";
+  }
+
+}

lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java

@@ -19,6 +19,7 @@ package org.apache.lucene.util;
 
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.Collections;
 
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -31,7 +32,7 @@ import org.apache.lucene.search.DocIdSetIterator;
  * 
  * @lucene.internal
  */
-public final class FixedBitSet extends DocIdSet implements MutableBits {
+public final class FixedBitSet implements MutableBits, Accountable {
 
   private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(FixedBitSet.class);
 
@@ -43,18 +44,20 @@ public final class FixedBitSet extends DocIdSet implements MutableBits {
     
     final int numBits, numWords;
     final long[] bits;
+    final long cost;
     int doc = -1;
     
     /** Creates an iterator over the given {@link FixedBitSet}. */
-    public FixedBitSetIterator(FixedBitSet bits) {
+    public FixedBitSetIterator(FixedBitSet bits, long cost) {
-      this(bits.bits, bits.numBits, bits.numWords);
+      this(bits.bits, bits.numBits, bits.numWords, cost);
     }
     
     /** Creates an iterator over the given array of bits. */
-    public FixedBitSetIterator(long[] bits, int numBits, int wordLength) {
+    public FixedBitSetIterator(long[] bits, int numBits, int wordLength, long cost) {
       this.bits = bits;
       this.numBits = numBits;
       this.numWords = wordLength;
+      this.cost = cost;
     }
     
     @Override
@@ -69,7 +72,7 @@ public final class FixedBitSet extends DocIdSet implements MutableBits {
     
     @Override
     public long cost() {
-      return numBits;
+      return cost;
     }
     
     @Override
@@ -179,33 +182,22 @@ public final class FixedBitSet extends DocIdSet implements MutableBits {
     this.numBits = numBits;
     this.bits = storedBits;
   }
-  
-  @Override
-  public DocIdSetIterator iterator() {
-    return new FixedBitSetIterator(bits, numBits, numWords);
-  }
-
-  @Override
-  public Bits bits() {
-    return this;
-  }
 
   @Override
   public int length() {
     return numBits;
   }
 
-  /** This DocIdSet implementation is cacheable. */
-  @Override
-  public boolean isCacheable() {
-    return true;
-  }
-
   @Override
   public long ramBytesUsed() {
     return BASE_RAM_BYTES_USED + RamUsageEstimator.sizeOf(bits);
   }
 
+  @Override
+  public Iterable<? extends Accountable> getChildResources() {
+    return Collections.emptyList();
+  }
+
   /** Expert. */
   public long[] getBits() {
     return bits;

lucene/core/src/java/org/apache/lucene/util/RoaringDocIdSet.java

@@ -92,7 +92,7 @@ public class RoaringDocIdSet extends DocIdSet {
           sets[currentBlock] = new NotDocIdSet(BLOCK_SIZE, new ShortArrayDocIdSet(excludedDocs));
         } else {
           // Neither sparse nor super dense, use a fixed bit set
-          sets[currentBlock] = denseBuffer;
+          sets[currentBlock] = new FixedBitDocIdSet(denseBuffer, currentBlockCardinality);
         }
         denseBuffer = null;
       }

lucene/core/src/java/org/apache/lucene/util/SparseFixedBitDocIdSet.java

@@ -0,0 +1,71 @@
+package org.apache.lucene.util;
+
+/*
+ * 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 org.apache.lucene.search.DocIdSet;
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.util.SparseFixedBitSet.SparseFixedBitSetIterator;
+
+/**
+ * Implementation of the {@link DocIdSet} interface on top of a {@link SparseFixedBitSet}.
+ * @lucene.internal
+ */
+public class SparseFixedBitDocIdSet extends DocIdSet {
+
+  private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(SparseFixedBitDocIdSet.class);
+
+  private final SparseFixedBitSet set;
+  private final long cost;
+
+  /**
+   * Wrap the given {@link FixedBitSet} as a {@link DocIdSet}. The provided
+   * {@link FixedBitSet} should not be modified after having wrapped as a
+   * {@link DocIdSet}.
+   */
+  public SparseFixedBitDocIdSet(SparseFixedBitSet set, long cost) {
+    this.set = set;
+    this.cost = cost;
+  }
+
+  @Override
+  public SparseFixedBitSet bits() {
+    return set;
+  }
+
+  @Override
+  public boolean isCacheable() {
+    return true;
+  }
+
+  @Override
+  public DocIdSetIterator iterator() throws IOException {
+    return new SparseFixedBitSetIterator(set, cost);
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    return BASE_RAM_BYTES_USED + set.ramBytesUsed();
+  }
+
+  @Override
+  public String toString() {
+    return getClass().getSimpleName() + "(set=" + set + ",cost=" + cost + ")";
+  }
+}

lucene/core/src/java/org/apache/lucene/util/SparseFixedBitSet.java

@@ -18,8 +18,8 @@ package org.apache.lucene.util;
  */
 
 import java.io.IOException;
+import java.util.Collections;
 
-import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 
 /**
@@ -33,7 +33,7 @@ import org.apache.lucene.search.DocIdSetIterator;
  *
  * @lucene.internal
  */
-public class SparseFixedBitSet extends DocIdSet implements Bits {
+public class SparseFixedBitSet implements Bits, Accountable {
 
   private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(SparseFixedBitSet.class);
   private static final long SINGLE_ELEMENT_ARRAY_BYTES_USED = RamUsageEstimator.sizeOf(new long[1]);
@@ -68,21 +68,11 @@ public class SparseFixedBitSet extends DocIdSet implements Bits {
         + RamUsageEstimator.shallowSizeOf(bits);
   }
 
-  @Override
-  public boolean isCacheable() {
-    return true;
-  }
-
   @Override
   public int length() {
     return length;
   }
 
-  @Override
-  public Bits bits() throws IOException {
-    return this;
-  }
-
   private boolean consistent(int index) {
     assert index >= 0 && index < length : "index=" + index + ",length=" + length;
     return true;
@@ -218,14 +208,27 @@ public class SparseFixedBitSet extends DocIdSet implements Bits {
   }
 
   @Override
-  public DocIdSetIterator iterator() throws IOException {
+  public Iterable<? extends Accountable> getChildResources() {
-    return new Iterator();
+    return Collections.emptyList();
   }
 
-  class Iterator extends DocIdSetIterator {
+  /**
+   * A {@link DocIdSetIterator} which iterates over set bits in a
+   * {@link SparseFixedBitSet}.
+   */
+  public static class SparseFixedBitSetIterator extends DocIdSetIterator {
 
+    private final long[] indices;
+    private final long[][] bits;
+    private final long cost;
     private int doc = -1;
-    private int cost = -1;
+
+    /** Sole constructor. */
+    public SparseFixedBitSetIterator(SparseFixedBitSet set, long cost) {
+      indices = set.indices;
+      bits = set.bits;
+      this.cost = cost;
+    }
 
     @Override
     public int docID() {
@@ -315,13 +318,6 @@ public class SparseFixedBitSet extends DocIdSet implements Bits {
 
     @Override
     public long cost() {
-      // although constant-time, approximateCardinality is a bit expensive so
-      // we cache it to avoid performance traps eg. when sorting iterators by
-      // cost
-      if (cost < 0) {
-        cost = approximateCardinality();
-      }
-      assert cost >= 0;
       return cost;
     }
 

lucene/core/src/test/org/apache/lucene/search/MockFilter.java

@@ -18,6 +18,7 @@ package org.apache.lucene.search;
  */
 
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.Bits;
 
@@ -27,7 +28,8 @@ public class MockFilter extends Filter {
   @Override
   public DocIdSet getDocIdSet(LeafReaderContext context, Bits acceptDocs) {
     wasCalled = true;
-    return new FixedBitSet(context.reader().maxDoc());
+    FixedBitSet bits = new FixedBitSet(context.reader().maxDoc());
+    return new FixedBitDocIdSet(bits);
   }
 
   public void clear() {

lucene/core/src/test/org/apache/lucene/search/SingleDocTestFilter.java

@@ -17,12 +17,13 @@ package org.apache.lucene.search;
  * limitations under the License.
  */
 
+import java.io.IOException;
+
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
-import java.io.IOException;
-
 public class SingleDocTestFilter extends Filter {
   private int doc;
 
@@ -35,6 +36,6 @@ public class SingleDocTestFilter extends Filter {
     FixedBitSet bits = new FixedBitSet(context.reader().maxDoc());
     bits.set(doc);
     if (acceptDocs != null && !acceptDocs.get(doc)) bits.clear(doc);
-    return bits;
+    return new FixedBitDocIdSet(bits);
   }
 }

lucene/core/src/test/org/apache/lucene/search/TestCachingWrapperFilter.java

@@ -32,6 +32,7 @@ import org.apache.lucene.index.SlowCompositeReaderWrapper;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
@@ -264,7 +265,7 @@ public class TestCachingWrapperFilter extends LuceneTestCase {
     assertDocIdSetCacheable(reader, new Filter() {
       @Override
       public DocIdSet getDocIdSet(LeafReaderContext context, Bits acceptDocs) {
-        return new FixedBitSet(context.reader().maxDoc());
+        return new FixedBitDocIdSet(new FixedBitSet(context.reader().maxDoc()));
       }
     }, true);
 

lucene/core/src/test/org/apache/lucene/search/TestFilteredQuery.java

@@ -34,6 +34,7 @@ import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.FilteredQuery.FilterStrategy;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
@@ -104,7 +105,7 @@ public class TestFilteredQuery extends LuceneTestCase {
         FixedBitSet bitset = new FixedBitSet(context.reader().maxDoc());
         if (acceptDocs.get(1)) bitset.set(1);
         if (acceptDocs.get(3)) bitset.set(3);
-        return bitset;
+        return new FixedBitDocIdSet(bitset);
       }
     };
   }
@@ -185,7 +186,7 @@ public class TestFilteredQuery extends LuceneTestCase {
         assertNull("acceptDocs should be null, as we have an index without deletions", acceptDocs);
         FixedBitSet bitset = new FixedBitSet(context.reader().maxDoc());
         bitset.set(0, Math.min(5, bitset.length()));
-        return bitset;
+        return new FixedBitDocIdSet(bitset);
       }
     };
   }

lucene/core/src/test/org/apache/lucene/search/TestFilteredSearch.java

@@ -31,6 +31,7 @@ import org.apache.lucene.index.Term;
 import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 
@@ -98,7 +99,7 @@ public class TestFilteredSearch extends LuceneTestCase {
           set.set(docId-docBase);
         }
       }
-      return set.cardinality() == 0 ? null:set;
+      return set.cardinality() == 0 ? null : new FixedBitDocIdSet(set);
     }
   }
 

lucene/core/src/test/org/apache/lucene/search/TestScorerPerf.java

@@ -14,6 +14,7 @@ import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 
@@ -145,7 +146,7 @@ public class TestScorerPerf extends LuceneTestCase {
       @Override
       public DocIdSet getDocIdSet (LeafReaderContext context, Bits acceptDocs) {
         assertNull("acceptDocs should be null, as we have an index without deletions", acceptDocs);
-        return rnd;
+        return new FixedBitDocIdSet(rnd);
       }
     });
     bq.add(q, BooleanClause.Occur.MUST);

lucene/core/src/test/org/apache/lucene/search/TestSortRandom.java

@@ -39,6 +39,7 @@ import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
@@ -260,7 +261,7 @@ public class TestSortRandom extends LuceneTestCase {
         }
       }
 
-      return bits;
+      return new FixedBitDocIdSet(bits);
     }
   }
 }

lucene/core/src/test/org/apache/lucene/util/TestDocIdSetBuilder.java

@@ -60,8 +60,8 @@ public class TestDocIdSetBuilder extends LuceneTestCase {
       builder.or(b.build().iterator());
     }
     DocIdSet result = builder.build();
-    assertTrue(result instanceof SparseFixedBitSet);
+    assertTrue(result instanceof SparseFixedBitDocIdSet);
-    assertEquals(ref, result);
+    assertEquals(new FixedBitDocIdSet(ref), result);
   }
 
   public void testDense() throws IOException {
@@ -84,8 +84,8 @@ public class TestDocIdSetBuilder extends LuceneTestCase {
       builder.or(b.build().iterator());
     }
     DocIdSet result = builder.build();
-    assertTrue(result instanceof FixedBitSet);
+    assertTrue(result instanceof FixedBitDocIdSet);
-    assertEquals(ref, result);
+    assertEquals(new FixedBitDocIdSet(ref), result);
   }
 
 }

lucene/core/src/test/org/apache/lucene/util/TestFixedBitSet.java

@@ -21,16 +21,17 @@ import java.io.IOException;
 import java.util.BitSet;
 
 import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 
-public class TestFixedBitSet extends BaseDocIdSetTestCase<FixedBitSet> {
+public class TestFixedBitSet extends BaseDocIdSetTestCase<FixedBitDocIdSet> {
 
   @Override
-  public FixedBitSet copyOf(BitSet bs, int length) throws IOException {
+  public FixedBitDocIdSet copyOf(BitSet bs, int length) throws IOException {
     final FixedBitSet set = new FixedBitSet(length);
     for (int doc = bs.nextSetBit(0); doc != -1; doc = bs.nextSetBit(doc + 1)) {
       set.set(doc);
     }
-    return set;
+    return new FixedBitDocIdSet(set);
   }
 
   void doGet(BitSet a, FixedBitSet b) {
@@ -81,7 +82,7 @@ public class TestFixedBitSet extends BaseDocIdSetTestCase<FixedBitSet> {
 
   void doIterate1(BitSet a, FixedBitSet b) throws IOException {
     int aa=-1,bb=-1;
-    DocIdSetIterator iterator = b.iterator();
+    DocIdSetIterator iterator = new FixedBitSetIterator(b, 0);
     do {
       aa = a.nextSetBit(aa+1);
       bb = (bb < b.length() && random().nextBoolean()) ? iterator.nextDoc() : iterator.advance(bb + 1);
@@ -91,7 +92,7 @@ public class TestFixedBitSet extends BaseDocIdSetTestCase<FixedBitSet> {
 
   void doIterate2(BitSet a, FixedBitSet b) throws IOException {
     int aa=-1,bb=-1;
-    DocIdSetIterator iterator = b.iterator();
+    DocIdSetIterator iterator = new FixedBitSetIterator(b, 0);
     do {
       aa = a.nextSetBit(aa+1);
       bb = random().nextBoolean() ? iterator.nextDoc() : iterator.advance(bb + 1);

lucene/core/src/test/org/apache/lucene/util/TestNotDocIdSet.java

@@ -30,7 +30,7 @@ public class TestNotDocIdSet extends BaseDocIdSetTestCase<NotDocIdSet> {
     for (int doc = bs.nextClearBit(0); doc < length; doc = bs.nextClearBit(doc + 1)) {
       set.set(doc);
     }
-    return new NotDocIdSet(length, set);
+    return new NotDocIdSet(length, new FixedBitDocIdSet(set));
   }
 
   @Override
@@ -48,7 +48,7 @@ public class TestNotDocIdSet extends BaseDocIdSetTestCase<NotDocIdSet> {
 
   public void testBits() throws IOException {
     assertNull(new NotDocIdSet(3, DocIdSet.EMPTY).bits());
-    assertNotNull(new NotDocIdSet(3, new FixedBitSet(3)).bits());
+    assertNotNull(new NotDocIdSet(3, new FixedBitDocIdSet(new FixedBitSet(3))).bits());
   }
 
 }

lucene/core/src/test/org/apache/lucene/util/TestSparseFixedBitSet.java

@@ -23,10 +23,10 @@ import java.util.BitSet;
 import java.util.Collections;
 import java.util.List;
 
-public class TestSparseFixedBitSet extends BaseDocIdSetTestCase<SparseFixedBitSet> {
+public class TestSparseFixedBitSet extends BaseDocIdSetTestCase<SparseFixedBitDocIdSet> {
 
   @Override
-  public SparseFixedBitSet copyOf(BitSet bs, int length) throws IOException {
+  public SparseFixedBitDocIdSet copyOf(BitSet bs, int length) throws IOException {
     final SparseFixedBitSet set = new SparseFixedBitSet(length);
     // SparseFixedBitSet can be sensitive to the order of insertion so
     // randomize insertion a bit
@@ -45,15 +45,15 @@ public class TestSparseFixedBitSet extends BaseDocIdSetTestCase<SparseFixedBitSe
     for (int i : buffer) {
       set.set(i);
     }
-    return set;
+    return new SparseFixedBitDocIdSet(set, set.approximateCardinality());
   }
 
   @Override
-  public void assertEquals(int numBits, BitSet ds1, SparseFixedBitSet ds2) throws IOException {
+  public void assertEquals(int numBits, BitSet ds1, SparseFixedBitDocIdSet ds2) throws IOException {
     for (int i = 0; i < numBits; ++i) {
-      assertEquals(ds1.get(i), ds2.get(i));
+      assertEquals(ds1.get(i), ds2.bits().get(i));
     }
-    assertEquals(ds1.cardinality(), ds2.cardinality());
+    assertEquals(ds1.cardinality(), ds2.bits().cardinality());
     super.assertEquals(numBits, ds1, ds2);
   }
 

lucene/facet/src/java/org/apache/lucene/facet/FacetsCollector.java

@@ -40,6 +40,7 @@ import org.apache.lucene.search.TopFieldCollector;
 import org.apache.lucene.search.TopFieldDocs;
 import org.apache.lucene.search.TopScoreDocCollector;
 import org.apache.lucene.util.ArrayUtil;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /** Collects hits for subsequent faceting.  Once you've run
@@ -128,7 +129,7 @@ public class FacetsCollector extends SimpleCollector {
       
       @Override
       public DocIdSet getDocIdSet() {
-        return bits;
+        return new FixedBitDocIdSet(bits);
       }
     };
   }

lucene/facet/src/java/org/apache/lucene/facet/RandomSamplingFacetsCollector.java

@@ -26,6 +26,7 @@ import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -212,7 +213,7 @@ public class RandomSamplingFacetsCollector extends FacetsCollector {
         }
       }
       
-      return new MatchingDocs(docs.context, sampleDocs, docs.totalHits, null);
+      return new MatchingDocs(docs.context, new FixedBitDocIdSet(sampleDocs), docs.totalHits, null);
     } catch (IOException e) {
       throw new RuntimeException();
     }

lucene/facet/src/test/org/apache/lucene/facet/TestDrillSideways.java

@@ -58,6 +58,7 @@ import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.InPlaceMergeSorter;
@@ -657,7 +658,7 @@ public class TestDrillSideways extends FacetTestCase {
                   bits.set(docID);
                 }
               }
-              return bits;
+              return new FixedBitDocIdSet(bits);
             }
           };
       } else {

lucene/facet/src/test/org/apache/lucene/facet/range/TestRangeFacetCounts.java

@@ -65,6 +65,7 @@ import org.apache.lucene.search.NumericRangeFilter;
 import org.apache.lucene.search.NumericRangeQuery;
 import org.apache.lucene.search.QueryWrapperFilter;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.TestUtil;
@@ -926,7 +927,7 @@ public class TestRangeFacetCounts extends FacetTestCase {
             final FixedBitSet cached = new FixedBitSet(reader.maxDoc());
             filterWasUsed.set(true);
             cached.or(iterator);
-            return cached;
+            return new FixedBitDocIdSet(cached);
           }
         };
     } else {

lucene/grouping/src/test/org/apache/lucene/search/grouping/AllGroupHeadsCollectorTest.java

@@ -43,7 +43,6 @@ import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.queries.function.ValueSource;
 import org.apache.lucene.queries.function.valuesource.BytesRefFieldSource;
-import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.ScoreDoc;
 import org.apache.lucene.search.Sort;
@@ -406,9 +405,7 @@ public class AllGroupHeadsCollectorTest extends LuceneTestCase {
       expected.set(expectedDoc);
     }
 
-    int docId;
+    for (int docId = expected.nextSetBit(0); docId != -1; docId = docId + 1 >= expected.length() ? -1 : expected.nextSetBit(docId + 1)) {
-    DocIdSetIterator iterator = expected.iterator();
-    while ((docId = iterator.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
       if (!actual.get(docId)) {
         return false;
       }

lucene/join/src/java/org/apache/lucene/search/join/FixedBitSetCachingWrapperFilter.java

@@ -26,6 +26,7 @@ import org.apache.lucene.search.CachingWrapperFilter;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Filter;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /** A {@link CachingWrapperFilter} that caches sets using a {@link FixedBitSet},
@@ -42,7 +43,7 @@ public final class FixedBitSetCachingWrapperFilter extends CachingWrapperFilter
       throws IOException {
     if (docIdSet == null) {
       return EMPTY;
-    } else if (docIdSet instanceof FixedBitSet) {
+    } else if (docIdSet instanceof FixedBitDocIdSet) {
       // this is different from CachingWrapperFilter: even when the DocIdSet is
       // cacheable, we convert it to a FixedBitSet since we require all the
       // cached filters to be FixedBitSets
@@ -54,7 +55,7 @@ public final class FixedBitSetCachingWrapperFilter extends CachingWrapperFilter
       } else {
         final FixedBitSet copy = new FixedBitSet(reader.maxDoc());
         copy.or(it);
-        return copy;
+        return new FixedBitDocIdSet(copy);
       }
     }
   }

lucene/join/src/java/org/apache/lucene/search/join/TermsIncludingScoreQuery.java

@@ -21,25 +21,26 @@ import java.io.IOException;
 import java.util.Locale;
 import java.util.Set;
 
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.DocsEnum;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
-import org.apache.lucene.search.LeafCollector;
+import org.apache.lucene.search.BulkScorer;
 import org.apache.lucene.search.ComplexExplanation;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.LeafCollector;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.Scorer;
-import org.apache.lucene.search.BulkScorer;
 import org.apache.lucene.search.Weight;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.BytesRefHash;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 
 class TermsIncludingScoreQuery extends Query {
 
@@ -328,7 +329,7 @@ class TermsIncludingScoreQuery extends Query {
       FixedBitSet matchingDocs = new FixedBitSet(maxDoc);
       this.scores = new float[maxDoc];
       fillDocsAndScores(matchingDocs, acceptDocs, termsEnum);
-      this.matchingDocsIterator = matchingDocs.iterator();
+      this.matchingDocsIterator = new FixedBitSetIterator(matchingDocs, cost);
       this.cost = cost;
     }
 

lucene/join/src/java/org/apache/lucene/search/join/ToChildBlockJoinQuery.java

@@ -22,8 +22,8 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Set;
 
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.Explanation;
@@ -33,6 +33,7 @@ import org.apache.lucene.search.Query;
 import org.apache.lucene.search.Scorer;
 import org.apache.lucene.search.Weight;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -144,11 +145,11 @@ public class ToChildBlockJoinQuery extends Query {
         // No matches
         return null;
       }
-      if (!(parents instanceof FixedBitSet)) {
+      if (!(parents instanceof FixedBitDocIdSet)) {
         throw new IllegalStateException("parentFilter must return FixedBitSet; got " + parents);
       }
 
-      return new ToChildBlockJoinScorer(this, parentScorer, (FixedBitSet) parents, doScores, acceptDocs);
+      return new ToChildBlockJoinScorer(this, parentScorer, ((FixedBitDocIdSet) parents).bits(), doScores, acceptDocs);
     }
 
     @Override

lucene/join/src/java/org/apache/lucene/search/join/ToParentBlockJoinFieldComparator.java

@@ -17,15 +17,16 @@ package org.apache.lucene.search.join;
  * limitations under the License.
  */
 
+import java.io.IOException;
+
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.FieldComparator;
 import org.apache.lucene.search.Filter;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
-import java.io.IOException;
-
 /**
  * A field comparator that allows parent documents to be sorted by fields
  * from the nested / child documents.
@@ -69,8 +70,8 @@ public abstract class ToParentBlockJoinFieldComparator extends FieldComparator<O
     DocIdSet innerDocuments = childFilter.getDocIdSet(context, null);
     if (isEmpty(innerDocuments)) {
       this.childDocuments = null;
-    } else if (innerDocuments instanceof FixedBitSet) {
+    } else if (innerDocuments instanceof FixedBitDocIdSet) {
-      this.childDocuments = (FixedBitSet) innerDocuments;
+      this.childDocuments = ((FixedBitDocIdSet) innerDocuments).bits();
     } else {
       DocIdSetIterator iterator = innerDocuments.iterator();
       if (iterator != null) {
@@ -82,8 +83,8 @@ public abstract class ToParentBlockJoinFieldComparator extends FieldComparator<O
     DocIdSet rootDocuments = parentFilter.getDocIdSet(context, null);
     if (isEmpty(rootDocuments)) {
       this.parentDocuments = null;
-    } else if (rootDocuments instanceof FixedBitSet) {
+    } else if (rootDocuments instanceof FixedBitDocIdSet) {
-      this.parentDocuments = (FixedBitSet) rootDocuments;
+      this.parentDocuments = ((FixedBitDocIdSet) rootDocuments).bits();
     } else {
       DocIdSetIterator iterator = rootDocuments.iterator();
       if (iterator != null) {

lucene/join/src/java/org/apache/lucene/search/join/ToParentBlockJoinQuery.java

@@ -23,9 +23,9 @@ import java.util.Collections;
 import java.util.Locale;
 import java.util.Set;
 
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.ComplexExplanation;
 import org.apache.lucene.search.DocIdSet;
@@ -39,6 +39,7 @@ import org.apache.lucene.search.Weight;
 import org.apache.lucene.search.grouping.TopGroups;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -183,11 +184,11 @@ public class ToParentBlockJoinQuery extends Query {
         // No matches
         return null;
       }
-      if (!(parents instanceof FixedBitSet)) {
+      if (!(parents instanceof FixedBitDocIdSet)) {
         throw new IllegalStateException("parentFilter must return FixedBitSet; got " + parents);
       }
 
-      return new BlockJoinScorer(this, childScorer, (FixedBitSet) parents, firstChildDoc, scoreMode, acceptDocs);
+      return new BlockJoinScorer(this, childScorer, ((FixedBitDocIdSet) parents).bits(), firstChildDoc, scoreMode, acceptDocs);
     }
 
     @Override

lucene/join/src/test/org/apache/lucene/search/join/TestBlockJoin.java

@@ -359,7 +359,7 @@ public class TestBlockJoin extends LuceneTestCase {
     final List<LeafReaderContext> leaves = reader.leaves();
     final int subIndex = ReaderUtil.subIndex(childDocID, leaves);
     final LeafReaderContext leaf = leaves.get(subIndex);
-    final FixedBitSet bits = (FixedBitSet) parents.getDocIdSet(leaf, null);
+    final FixedBitSet bits = (FixedBitSet) parents.getDocIdSet(leaf, null).bits();
     return leaf.reader().document(bits.nextSetBit(childDocID - leaf.docBase));
   }
   

lucene/join/src/test/org/apache/lucene/search/join/TestJoinUtil.java

@@ -37,12 +37,12 @@ import org.apache.lucene.document.Field;
 import org.apache.lucene.document.SortedDocValuesField;
 import org.apache.lucene.document.SortedSetDocValuesField;
 import org.apache.lucene.document.TextField;
-import org.apache.lucene.index.LeafReader;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.DocsEnum;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiFields;
 import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.index.SlowCompositeReaderWrapper;
@@ -67,6 +67,7 @@ import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
 import org.junit.Test;
@@ -504,12 +505,12 @@ public class TestJoinUtil extends LuceneTestCase {
         // Asserting bit set...
         if (VERBOSE) {
           System.out.println("expected cardinality:" + expectedResult.cardinality());
-          DocIdSetIterator iterator = expectedResult.iterator();
+          DocIdSetIterator iterator = new FixedBitSetIterator(expectedResult, expectedResult.cardinality());
           for (int doc = iterator.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iterator.nextDoc()) {
             System.out.println(String.format(Locale.ROOT, "Expected doc[%d] with id value %s", doc, indexSearcher.doc(doc).get("id")));
           }
           System.out.println("actual cardinality:" + actualResult.cardinality());
-          iterator = actualResult.iterator();
+          iterator = new FixedBitSetIterator(actualResult, actualResult.cardinality());
           for (int doc = iterator.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iterator.nextDoc()) {
             System.out.println(String.format(Locale.ROOT, "Actual doc[%d] with id value %s", doc, indexSearcher.doc(doc).get("id")));
           }

lucene/misc/src/java/org/apache/lucene/index/PKIndexSplitter.java

@@ -28,6 +28,7 @@ import org.apache.lucene.search.TermRangeFilter;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 import org.apache.lucene.util.IOUtils;
 
 /**
@@ -141,7 +142,7 @@ public class PKIndexSplitter {
       if (in.hasDeletions()) {
         final Bits oldLiveDocs = in.getLiveDocs();
         assert oldLiveDocs != null;
-        final DocIdSetIterator it = bits.iterator();
+        final DocIdSetIterator it = new FixedBitSetIterator(bits, 0L); // the cost is not useful here
         for (int i = it.nextDoc(); i < maxDoc; i = it.nextDoc()) {
           if (!oldLiveDocs.get(i)) {
             // we can safely modify the current bit, as the iterator already stepped over it:

lucene/misc/src/java/org/apache/lucene/index/sorter/BlockJoinComparatorSource.java

@@ -30,6 +30,7 @@ import org.apache.lucene.search.ScoreDoc; // javadocs
 import org.apache.lucene.search.Scorer;
 import org.apache.lucene.search.Sort;
 import org.apache.lucene.search.SortField;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -148,10 +149,10 @@ public class BlockJoinComparatorSource extends FieldComparatorSource {
         if (parents == null) {
           throw new IllegalStateException("LeafReader " + context.reader() + " contains no parents!");
         }
-        if (!(parents instanceof FixedBitSet)) {
+        if (!(parents instanceof FixedBitDocIdSet)) {
           throw new IllegalStateException("parentFilter must return FixedBitSet; got " + parents);
         }
-        parentBits = (FixedBitSet) parents;
+        parentBits = (FixedBitSet) parents.bits();
         for (int i = 0; i < parentComparators.length; i++) {
           parentComparators[i] = parentComparators[i].setNextReader(context);
         }

lucene/misc/src/test/org/apache/lucene/index/sorter/TestBlockJoinSorter.java

@@ -41,6 +41,7 @@ import org.apache.lucene.search.Sort;
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.util.ArrayUtil;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 
@@ -57,7 +58,7 @@ public class TestBlockJoinSorter extends LuceneTestCase {
         throws IOException {
       final FixedBitSet cached = new FixedBitSet(reader.maxDoc());
       cached.or(iterator);
-      return cached;
+      return new FixedBitDocIdSet(cached);
     }
 
   }
@@ -90,7 +91,7 @@ public class TestBlockJoinSorter extends LuceneTestCase {
 
     final LeafReader reader = getOnlySegmentReader(indexReader);
     final Filter parentsFilter = new FixedBitSetCachingWrapperFilter(new QueryWrapperFilter(new TermQuery(new Term("parent", "true"))));
-    final FixedBitSet parentBits = (FixedBitSet) parentsFilter.getDocIdSet(reader.getContext(), null);
+    final FixedBitSet parentBits = (FixedBitSet) parentsFilter.getDocIdSet(reader.getContext(), null).bits();
     final NumericDocValues parentValues = reader.getNumericDocValues("parent_val");
     final NumericDocValues childValues = reader.getNumericDocValues("child_val");
 

lucene/misc/src/test/org/apache/lucene/uninverting/TestFieldCacheSortRandom.java

@@ -52,6 +52,7 @@ import org.apache.lucene.store.Directory;
 import org.apache.lucene.uninverting.UninvertingReader.Type;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
@@ -290,7 +291,7 @@ public class TestFieldCacheSortRandom extends LuceneTestCase {
         }
       }
 
-      return bits;
+      return new FixedBitDocIdSet(bits);
     }
   }
 }

lucene/queries/src/java/org/apache/lucene/queries/BooleanFilter.java

@@ -30,6 +30,7 @@ import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Filter;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 /**
@@ -98,7 +99,10 @@ public class BooleanFilter extends Filter implements Iterable<FilterClause> {
       }
     }
 
-    return BitsFilteredDocIdSet.wrap(res, acceptDocs);
+    if (res == null) {
+      return null;
+    }
+    return BitsFilteredDocIdSet.wrap(new FixedBitDocIdSet(res), acceptDocs);
   }
 
   private static DocIdSetIterator getDISI(Filter filter, LeafReaderContext context)

lucene/queries/src/test/org/apache/lucene/queries/BooleanFilterTest.java

@@ -17,6 +17,8 @@ package org.apache.lucene.queries;
  * limitations under the License.
  */
 
+import java.io.IOException;
+
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.analysis.MockTokenizer;
 import org.apache.lucene.document.Document;
@@ -27,19 +29,18 @@ import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.index.SlowCompositeReaderWrapper;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.BooleanClause.Occur;
+import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Filter;
-import org.apache.lucene.search.TermRangeFilter;
-import org.apache.lucene.search.DocIdSet;
-import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.QueryWrapperFilter;
+import org.apache.lucene.search.TermQuery;
+import org.apache.lucene.search.TermRangeFilter;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 
-import java.io.IOException;
-
 public class BooleanFilterTest extends LuceneTestCase {
   private Directory directory;
   private LeafReader reader;
@@ -93,7 +94,7 @@ public class BooleanFilterTest extends LuceneTestCase {
     return new Filter() {
       @Override
       public DocIdSet getDocIdSet(LeafReaderContext context, Bits acceptDocs) {
-        return new FixedBitSet(context.reader().maxDoc());
+        return new FixedBitDocIdSet(new FixedBitSet(context.reader().maxDoc()));
       }
     };
   }

lucene/queries/src/test/org/apache/lucene/queries/TermsFilterTest.java

@@ -47,6 +47,7 @@ import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
@@ -81,20 +82,20 @@ public class TermsFilterTest extends LuceneTestCase {
 
     List<Term> terms = new ArrayList<>();
     terms.add(new Term(fieldName, "19"));
-    FixedBitSet bits = (FixedBitSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
+    FixedBitDocIdSet bits = (FixedBitDocIdSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
     assertNull("Must match nothing", bits);
 
     terms.add(new Term(fieldName, "20"));
-    bits = (FixedBitSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
+    bits = (FixedBitDocIdSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
-    assertEquals("Must match 1", 1, bits.cardinality());
+    assertEquals("Must match 1", 1, bits.bits().cardinality());
 
     terms.add(new Term(fieldName, "10"));
-    bits = (FixedBitSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
+    bits = (FixedBitDocIdSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
-    assertEquals("Must match 2", 2, bits.cardinality());
+    assertEquals("Must match 2", 2, bits.bits().cardinality());
 
     terms.add(new Term(fieldName, "00"));
-    bits = (FixedBitSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
+    bits = (FixedBitDocIdSet) termsFilter(random().nextBoolean(), terms).getDocIdSet(context, context.reader().getLiveDocs());
-    assertEquals("Must match 2", 2, bits.cardinality());
+    assertEquals("Must match 2", 2, bits.bits().cardinality());
 
     reader.close();
     rd.close();
@@ -126,8 +127,8 @@ public class TermsFilterTest extends LuceneTestCase {
       if (context.reader().docFreq(new Term(fieldName, "content1")) == 0) {
         assertNull(docIdSet);
       } else {
-        FixedBitSet bits = (FixedBitSet) docIdSet;
+        FixedBitDocIdSet bits = (FixedBitDocIdSet) docIdSet;
-        assertTrue("Must be >= 0", bits.cardinality() >= 0);      
+        assertTrue("Must be >= 0", bits.bits().cardinality() >= 0);      
       }
     }
     multi.close();
@@ -163,8 +164,8 @@ public class TermsFilterTest extends LuceneTestCase {
     LeafReaderContext context = reader.leaves().get(0);
     TermsFilter tf = new TermsFilter(terms);
 
-    FixedBitSet bits = (FixedBitSet) tf.getDocIdSet(context, context.reader().getLiveDocs());
+    FixedBitDocIdSet bits = (FixedBitDocIdSet) tf.getDocIdSet(context, context.reader().getLiveDocs());
-    assertEquals("Must be num fields - 1 since we skip only one field", num-1, bits.cardinality());  
+    assertEquals("Must be num fields - 1 since we skip only one field", num-1, bits.bits().cardinality());  
     reader.close();
     dir.close();
   }
@@ -199,8 +200,8 @@ public class TermsFilterTest extends LuceneTestCase {
     LeafReaderContext context = reader.leaves().get(0);
     TermsFilter tf = new TermsFilter(new ArrayList<>(terms));
 
-    FixedBitSet bits = (FixedBitSet) tf.getDocIdSet(context, context.reader().getLiveDocs());
+    FixedBitDocIdSet bits = (FixedBitDocIdSet) tf.getDocIdSet(context, context.reader().getLiveDocs());
-    assertEquals(context.reader().numDocs(), bits.cardinality());  
+    assertEquals(context.reader().numDocs(), bits.bits().cardinality());  
     reader.close();
     dir.close();
   }

lucene/sandbox/src/java/org/apache/lucene/sandbox/queries/DuplicateFilter.java

@@ -29,7 +29,9 @@ import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Filter;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.SparseFixedBitDocIdSet;
 import org.apache.lucene.util.SparseFixedBitSet;
 
 /**
@@ -93,88 +95,84 @@ public class DuplicateFilter extends Filter {
     }
   }
 
-  private SparseFixedBitSet correctBits(LeafReader reader, Bits acceptDocs) throws IOException {
+  private DocIdSet correctBits(LeafReader reader, Bits acceptDocs) throws IOException {
     SparseFixedBitSet bits = new SparseFixedBitSet(reader.maxDoc()); //assume all are INvalid
     Terms terms = reader.fields().terms(fieldName);
 
-    if (terms == null) {
+    if (terms != null) {
-      return bits;
+      TermsEnum termsEnum = terms.iterator(null);
+      DocsEnum docs = null;
+      while (true) {
+        BytesRef currTerm = termsEnum.next();
+        if (currTerm == null) {
+          break;
+        } else {
+          docs = termsEnum.docs(acceptDocs, docs, DocsEnum.FLAG_NONE);
+          int doc = docs.nextDoc();
+          if (doc != DocIdSetIterator.NO_MORE_DOCS) {
+            if (keepMode == KeepMode.KM_USE_FIRST_OCCURRENCE) {
+              bits.set(doc);
+            } else {
+              int lastDoc = doc;
+              while (true) {
+                lastDoc = doc;
+                doc = docs.nextDoc();
+                if (doc == DocIdSetIterator.NO_MORE_DOCS) {
+                  break;
+                }
+              }
+              bits.set(lastDoc);
+            }
+          }
+        }
+      }
     }
+    return new SparseFixedBitDocIdSet(bits, bits.approximateCardinality());
+  }
 
-    TermsEnum termsEnum = terms.iterator(null);
+  private DocIdSet fastBits(LeafReader reader, Bits acceptDocs) throws IOException {
-    DocsEnum docs = null;
+    FixedBitSet bits = new FixedBitSet(reader.maxDoc());
-    while (true) {
+    bits.set(0, reader.maxDoc()); //assume all are valid
-      BytesRef currTerm = termsEnum.next();
+    Terms terms = reader.fields().terms(fieldName);
-      if (currTerm == null) {
+
-        break;
+    if (terms != null) {
-      } else {
+      TermsEnum termsEnum = terms.iterator(null);
-        docs = termsEnum.docs(acceptDocs, docs, DocsEnum.FLAG_NONE);
+      DocsEnum docs = null;
-        int doc = docs.nextDoc();
+      while (true) {
-        if (doc != DocIdSetIterator.NO_MORE_DOCS) {
+        BytesRef currTerm = termsEnum.next();
-          if (keepMode == KeepMode.KM_USE_FIRST_OCCURRENCE) {
+        if (currTerm == null) {
-            bits.set(doc);
+          break;
-          } else {
+        } else {
-            int lastDoc = doc;
+          if (termsEnum.docFreq() > 1) {
+            // unset potential duplicates
+            docs = termsEnum.docs(acceptDocs, docs, DocsEnum.FLAG_NONE);
+            int doc = docs.nextDoc();
+            if (doc != DocIdSetIterator.NO_MORE_DOCS) {
+              if (keepMode == KeepMode.KM_USE_FIRST_OCCURRENCE) {
+                doc = docs.nextDoc();
+              }
+            }
+  
+            int lastDoc = -1;
             while (true) {
               lastDoc = doc;
+              bits.clear(lastDoc);
               doc = docs.nextDoc();
               if (doc == DocIdSetIterator.NO_MORE_DOCS) {
                 break;
               }
             }
-            bits.set(lastDoc);
+  
-          }
+            if (keepMode == KeepMode.KM_USE_LAST_OCCURRENCE) {
-        }
+              // restore the last bit
-      }
+              bits.set(lastDoc);
-    }
-    return bits;
-  }
-
-  private FixedBitSet fastBits(LeafReader reader, Bits acceptDocs) throws IOException {
-    FixedBitSet bits = new FixedBitSet(reader.maxDoc());
-    bits.set(0, reader.maxDoc()); //assume all are valid
-    Terms terms = reader.fields().terms(fieldName);
-
-    if (terms == null) {
-      return bits;
-    }
-
-    TermsEnum termsEnum = terms.iterator(null);
-    DocsEnum docs = null;
-    while (true) {
-      BytesRef currTerm = termsEnum.next();
-      if (currTerm == null) {
-        break;
-      } else {
-        if (termsEnum.docFreq() > 1) {
-          // unset potential duplicates
-          docs = termsEnum.docs(acceptDocs, docs, DocsEnum.FLAG_NONE);
-          int doc = docs.nextDoc();
-          if (doc != DocIdSetIterator.NO_MORE_DOCS) {
-            if (keepMode == KeepMode.KM_USE_FIRST_OCCURRENCE) {
-              doc = docs.nextDoc();
             }
           }
-
-          int lastDoc = -1;
-          while (true) {
-            lastDoc = doc;
-            bits.clear(lastDoc);
-            doc = docs.nextDoc();
-            if (doc == DocIdSetIterator.NO_MORE_DOCS) {
-              break;
-            }
-          }
-
-          if (keepMode == KeepMode.KM_USE_LAST_OCCURRENCE) {
-            // restore the last bit
-            bits.set(lastDoc);
-          }
         }
       }
     }
 
-    return bits;
+    return new FixedBitDocIdSet(bits);
   }
 
   public String getFieldName() {

lucene/sandbox/src/test/org/apache/lucene/search/TestTermAutomatonQuery.java

@@ -46,6 +46,7 @@ import org.apache.lucene.index.Term;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
@@ -637,7 +638,7 @@ public class TestTermAutomatonQuery extends LuceneTestCase {
         }
       }
 
-      return bits;
+      return new FixedBitDocIdSet(bits);
     }
   }
 }

lucene/spatial/src/java/org/apache/lucene/spatial/prefix/IntersectsPrefixTreeFilter.java

@@ -19,11 +19,13 @@ package org.apache.lucene.spatial.prefix;
 
 import com.spatial4j.core.shape.Shape;
 import com.spatial4j.core.shape.SpatialRelation;
+
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.spatial.prefix.tree.Cell;
 import org.apache.lucene.spatial.prefix.tree.SpatialPrefixTree;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 
 import java.io.IOException;
@@ -71,7 +73,7 @@ public class IntersectsPrefixTreeFilter extends AbstractVisitingPrefixTreeFilter
 
       @Override
       protected DocIdSet finish() {
-        return results;
+        return new FixedBitDocIdSet(results);
       }
 
       @Override

lucene/spatial/src/java/org/apache/lucene/spatial/prefix/WithinPrefixTreeFilter.java

@@ -17,6 +17,17 @@ package org.apache.lucene.spatial.prefix;
  * limitations under the License.
  */
 
+import java.io.IOException;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.DocIdSet;
+import org.apache.lucene.spatial.prefix.tree.Cell;
+import org.apache.lucene.spatial.prefix.tree.CellIterator;
+import org.apache.lucene.spatial.prefix.tree.SpatialPrefixTree;
+import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
+import org.apache.lucene.util.FixedBitSet;
+
 import com.spatial4j.core.context.SpatialContext;
 import com.spatial4j.core.distance.DistanceUtils;
 import com.spatial4j.core.shape.Circle;
@@ -24,15 +35,6 @@ import com.spatial4j.core.shape.Point;
 import com.spatial4j.core.shape.Rectangle;
 import com.spatial4j.core.shape.Shape;
 import com.spatial4j.core.shape.SpatialRelation;
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.search.DocIdSet;
-import org.apache.lucene.spatial.prefix.tree.Cell;
-import org.apache.lucene.spatial.prefix.tree.CellIterator;
-import org.apache.lucene.spatial.prefix.tree.SpatialPrefixTree;
-import org.apache.lucene.util.Bits;
-import org.apache.lucene.util.FixedBitSet;
-
-import java.io.IOException;
 
 /**
  * Finds docs where its indexed shape is {@link org.apache.lucene.spatial.query.SpatialOperation#IsWithin
@@ -134,7 +136,7 @@ public class WithinPrefixTreeFilter extends AbstractVisitingPrefixTreeFilter {
       @Override
       protected DocIdSet finish() {
         inside.andNot(outside);
-        return inside;
+        return new FixedBitDocIdSet(inside);
       }
 
       @Override

solr/core/src/java/org/apache/solr/handler/component/ExpandComponent.java

@@ -17,15 +17,17 @@
 
 package org.apache.solr.handler.component;
 
-import com.carrotsearch.hppc.IntObjectMap;
+import java.io.IOException;
-import com.carrotsearch.hppc.IntObjectOpenHashMap;
+import java.net.MalformedURLException;
-import com.carrotsearch.hppc.IntOpenHashSet;
+import java.net.URL;
-import com.carrotsearch.hppc.cursors.IntObjectCursor;
+import java.util.ArrayList;
-import com.carrotsearch.hppc.cursors.ObjectCursor;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
+import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.SortedDocValues;
 import org.apache.lucene.search.Collector;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -41,6 +43,7 @@ import org.apache.lucene.search.TopScoreDocCollector;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.CharsRefBuilder;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 import org.apache.solr.common.SolrDocumentList;
 import org.apache.solr.common.params.ExpandParams;
 import org.apache.solr.common.params.ShardParams;
@@ -60,13 +63,11 @@ import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.util.plugin.PluginInfoInitialized;
 import org.apache.solr.util.plugin.SolrCoreAware;
 
-import java.io.IOException;
+import com.carrotsearch.hppc.IntObjectMap;
-import java.net.MalformedURLException;
+import com.carrotsearch.hppc.IntObjectOpenHashMap;
-import java.net.URL;
+import com.carrotsearch.hppc.IntOpenHashSet;
-import java.util.ArrayList;
+import com.carrotsearch.hppc.cursors.IntObjectCursor;
-import java.util.HashMap;
+import com.carrotsearch.hppc.cursors.ObjectCursor;
-import java.util.List;
-import java.util.Map;
 
 /**
  * The ExpandComponent is designed to work with the CollapsingPostFilter.
@@ -307,7 +308,7 @@ public class ExpandComponent extends SearchComponent implements PluginInfoInitia
     public GroupExpandCollector(SortedDocValues docValues, FixedBitSet groupBits, IntOpenHashSet collapsedSet, int limit, Sort sort) throws IOException {
       int numGroups = collapsedSet.size();
       groups = new IntObjectOpenHashMap<>(numGroups * 2);
-      DocIdSetIterator iterator = groupBits.iterator();
+      DocIdSetIterator iterator = new FixedBitSetIterator(groupBits, 0); // cost is not useful here
       int group;
       while ((group = iterator.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
         Collector collector = (sort == null) ? TopScoreDocCollector.create(limit, true) : TopFieldCollector.create(sort, limit, false, false, false, true);

solr/core/src/java/org/apache/solr/response/SortingResponseWriter.java

@@ -17,11 +17,16 @@
     
 package org.apache.solr.response;
 
-import org.apache.lucene.index.LeafReaderContext;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.io.Writer;
+import java.util.List;
+
 import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiDocValues;
-import org.apache.lucene.index.SortedDocValues;
 import org.apache.lucene.index.NumericDocValues;
+import org.apache.lucene.index.SortedDocValues;
 import org.apache.lucene.index.SortedSetDocValues;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Sort;
@@ -29,31 +34,27 @@ import org.apache.lucene.search.SortField;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.CharsRefBuilder;
-import org.apache.lucene.util.LongValues;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
+import org.apache.lucene.util.LongValues;
 import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.request.SolrQueryRequest;
 import org.apache.solr.request.SolrRequestInfo;
+import org.apache.solr.schema.FieldType;
 import org.apache.solr.schema.IndexSchema;
 import org.apache.solr.schema.SchemaField;
-import org.apache.solr.schema.FieldType;
+import org.apache.solr.schema.StrField;
-import org.apache.solr.schema.TrieFloatField;
 import org.apache.solr.schema.TrieDoubleField;
+import org.apache.solr.schema.TrieFloatField;
 import org.apache.solr.schema.TrieIntField;
 import org.apache.solr.schema.TrieLongField;
-import org.apache.solr.schema.StrField;
 import org.apache.solr.search.SolrIndexSearcher;
 import org.apache.solr.search.SortSpec;
 import org.apache.solr.search.SyntaxError;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.IOException;
-import java.io.Writer;
-import java.io.PrintWriter;
-import java.util.List;
-
 
 public class SortingResponseWriter implements QueryResponseWriter {
 
@@ -127,8 +128,6 @@ public class SortingResponseWriter implements QueryResponseWriter {
     SortQueue queue = new SortQueue(queueSize, sortDoc);
     SortDoc[] outDocs = new SortDoc[queueSize];
 
-    long total = 0;
-
     while(count < totalHits) {
       //long begin = System.nanoTime();
       boolean commaNeeded = false;
@@ -136,7 +135,7 @@ public class SortingResponseWriter implements QueryResponseWriter {
       SortDoc top = queue.top();
       for(int i=0; i<leaves.size(); i++) {
         sortDoc.setNextReader(leaves.get(i));
-        DocIdSetIterator it = sets[i].iterator();
+        DocIdSetIterator it = new FixedBitSetIterator(sets[i], 0); // cost is not useful here
         int docId = -1;
         while((docId = it.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
           sortDoc.setValues(docId);

solr/core/src/java/org/apache/solr/search/BitDocSet.java

@@ -26,6 +26,7 @@ import org.apache.lucene.search.Filter;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
+import org.apache.lucene.util.FixedBitDocIdSet;
 
 /**
  * <code>BitDocSet</code> represents an unordered set of Lucene Document Ids
@@ -91,7 +92,7 @@ public class BitDocSet extends DocSetBase {
   @Override
   public DocIterator iterator() {
     return new DocIterator() {
-      private final FixedBitSetIterator iter = new FixedBitSetIterator(bits);
+      private final FixedBitSetIterator iter = new FixedBitSetIterator(bits, 0L); // cost is not useful here
       private int pos = iter.nextDoc();
       @Override
       public boolean hasNext() {
@@ -276,7 +277,7 @@ public class BitDocSet extends DocSetBase {
         final Bits acceptDocs2 = acceptDocs == null ? null : (reader.getLiveDocs() == acceptDocs ? null : acceptDocs);
 
         if (context.isTopLevel) {
-          return BitsFilteredDocIdSet.wrap(bs, acceptDocs);
+          return BitsFilteredDocIdSet.wrap(new FixedBitDocIdSet(bs), acceptDocs);
         }
 
         final int base = context.docBase;

solr/core/src/java/org/apache/solr/search/CollapsingQParserPlugin.java

@@ -22,8 +22,8 @@ import java.util.Arrays;
 import java.util.Iterator;
 import java.util.Map;
 
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.DocValues;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.SortedDocValues;
 import org.apache.lucene.queries.function.FunctionQuery;
@@ -35,6 +35,7 @@ import org.apache.lucene.search.Query;
 import org.apache.lucene.search.Scorer;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.lucene.util.FixedBitSet.FixedBitSetIterator;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.params.SolrParams;
@@ -49,8 +50,8 @@ import org.apache.solr.schema.TrieIntField;
 import org.apache.solr.schema.TrieLongField;
 
 import com.carrotsearch.hppc.FloatArrayList;
-import com.carrotsearch.hppc.IntOpenHashSet;
 import com.carrotsearch.hppc.IntIntOpenHashMap;
+import com.carrotsearch.hppc.IntOpenHashSet;
 import com.carrotsearch.hppc.cursors.IntIntCursor;
 
 /**
@@ -490,7 +491,7 @@ public class CollapsingQParserPlugin extends QParserPlugin {
       leafDelegate = delegate.getLeafCollector(contexts[currentContext]);
       DummyScorer dummy = new DummyScorer();
       leafDelegate.setScorer(dummy);
-      DocIdSetIterator it = collapsedSet.iterator();
+      DocIdSetIterator it = new FixedBitSetIterator(collapsedSet, 0L); // cost is not useful here
       int docId = -1;
       int nullScoreIndex = 0;
       while((docId = it.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
@@ -603,7 +604,7 @@ public class CollapsingQParserPlugin extends QParserPlugin {
       leafDelegate = delegate.getLeafCollector(contexts[currentContext]);
       DummyScorer dummy = new DummyScorer();
       leafDelegate.setScorer(dummy);
-      DocIdSetIterator it = fieldValueCollapse.getCollapsedSet().iterator();
+      DocIdSetIterator it = new FixedBitSetIterator(fieldValueCollapse.getCollapsedSet(), 0); // cost is not useful here
       int docId = -1;
       int nullScoreIndex = 0;
       float[] scores = fieldValueCollapse.getScores();

solr/core/src/java/org/apache/solr/search/DocSetBase.java

@@ -24,6 +24,7 @@ import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.search.Filter;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.solr.common.SolrException;
 
@@ -171,7 +172,7 @@ abstract class DocSetBase implements DocSet {
         final Bits acceptDocs2 = acceptDocs == null ? null : (reader.getLiveDocs() == acceptDocs ? null : acceptDocs);
 
         if (context.isTopLevel) {
-          return BitsFilteredDocIdSet.wrap(bs, acceptDocs);
+          return BitsFilteredDocIdSet.wrap(new FixedBitDocIdSet(bs), acceptDocs);
         }
 
         final int base = context.docBase;

solr/core/src/test/org/apache/solr/search/TestDocSet.java

@@ -22,14 +22,14 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.Random;
 
-import org.apache.lucene.index.LeafReader;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.FieldInfos;
 import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexReaderContext;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiReader;
 import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.SortedDocValues;
@@ -68,7 +68,7 @@ public class TestDocSet extends LuceneTestCase {
 
   public DocSet getHashDocSet(FixedBitSet bs) {
     int[] docs = new int[bs.cardinality()];
-    FixedBitSetIterator iter = new FixedBitSetIterator(bs);
+    FixedBitSetIterator iter = new FixedBitSetIterator(bs, 0);
     for (int i=0; i<docs.length; i++) {
       docs[i] = iter.nextDoc();
     }
@@ -77,7 +77,7 @@ public class TestDocSet extends LuceneTestCase {
 
   public DocSet getIntDocSet(FixedBitSet bs) {
     int[] docs = new int[bs.cardinality()];
-    FixedBitSetIterator iter = new FixedBitSetIterator(bs);
+    FixedBitSetIterator iter = new FixedBitSetIterator(bs, 0);
     for (int i=0; i<docs.length; i++) {
       docs[i] = iter.nextDoc();
     }
@@ -95,7 +95,7 @@ public class TestDocSet extends LuceneTestCase {
     int offset = 3;
     int end = offset + len;
 
-    FixedBitSetIterator iter = new FixedBitSetIterator(bs);
+    FixedBitSetIterator iter = new FixedBitSetIterator(bs, 0);
     // put in opposite order... DocLists are not ordered.
     for (int i=end-1; i>=offset; i--) {
       arr[i] = iter.nextDoc();

solr/core/src/test/org/apache/solr/search/TestSort.java

@@ -30,18 +30,18 @@ import org.apache.lucene.analysis.core.SimpleAnalyzer;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.StringField;
-import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
-import org.apache.lucene.search.LeafCollector;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.BitsFilteredDocIdSet;
 import org.apache.lucene.search.Collector;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.Filter;
-import org.apache.lucene.search.FilterLeafCollector;
 import org.apache.lucene.search.FilterCollector;
+import org.apache.lucene.search.FilterLeafCollector;
 import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.LeafCollector;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.ScoreDoc;
 import org.apache.lucene.search.Sort;
@@ -53,6 +53,7 @@ import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.RAMDirectory;
 import org.apache.lucene.uninverting.UninvertingReader;
 import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitDocIdSet;
 import org.apache.lucene.util.FixedBitSet;
 import org.apache.lucene.util.TestUtil;
 import org.apache.solr.SolrTestCaseJ4;
@@ -339,7 +340,7 @@ public class TestSort extends SolrTestCaseJ4 {
     for (int i=0; i<n; i++) {
       obs.set(r.nextInt(sz));
     }
-    return obs;
+    return new FixedBitDocIdSet(obs);
   }  
   
 

solr/core/src/test/org/apache/solr/util/BitSetPerf.java

@@ -172,7 +172,7 @@ public class BitSetPerf {
         for (int i=0; i<numSets; i++) {
           if (impl=="open") {
             final FixedBitSet set = osets[i];
-            final FixedBitSetIterator iterator = new FixedBitSetIterator(set);
+            final FixedBitSetIterator iterator = new FixedBitSetIterator(set, 0);
             for(int next=iterator.nextDoc(); next>=0; next=iterator.nextDoc()) {
               ret += next;
             }