org.apache.lucene.util.BitSet Java Examples

public void testSimple() throws Exception {
  Directory dir = newDirectory();
  IndexWriterConfig iwc = newIndexWriterConfig().setMergePolicy(NoMergePolicy.INSTANCE);
  RandomIndexWriter w = new RandomIndexWriter(random(), dir, iwc);
  w.addDocument(new Document());
  DirectoryReader reader = w.getReader();

  QueryBitSetProducer producer = new QueryBitSetProducer(new MatchNoDocsQuery());
  assertNull(producer.getBitSet(reader.leaves().get(0)));
  assertEquals(1, producer.cache.size());

  producer = new QueryBitSetProducer(new MatchAllDocsQuery());
  BitSet bitSet = producer.getBitSet(reader.leaves().get(0));
  assertEquals(1, bitSet.length());
  assertEquals(true, bitSet.get(0));
  assertEquals(1, producer.cache.size());

  IOUtils.close(reader, w, dir);
}
 

private int doNext(int doc) throws IOException {
  advanceLead: for (;; doc = lead.nextDoc()) {
    if (doc >= minLength) {
      return NO_MORE_DOCS;
    }
    for (BitSet bitSet : bitSets) {
      if (bitSet.get(doc) == false) {
        continue advanceLead;
      }
    }
    for (BitSetIterator iterator : bitSetIterators) {
      iterator.setDocId(doc);
    }
    return doc;
  }
}
 

private void assertAdvanceBeyondEnd(BitSet set, Directory dir) throws IOException {
  final int cardinality = set.cardinality();
  final byte denseRankPower = 9; // Not tested here so fixed to isolate factors
  long length;
  int jumpTableentryCount;
  try (IndexOutput out = dir.createOutput("bar", IOContext.DEFAULT)) {
    jumpTableentryCount = IndexedDISI.writeBitSet(new BitSetIterator(set, cardinality), out, denseRankPower);
  }

  try (IndexInput in = dir.openInput("bar", IOContext.DEFAULT)) {
    BitSetIterator disi2 = new BitSetIterator(set, cardinality);
    int doc = disi2.docID();
    int index = 0;
    while (doc < cardinality) {
      doc = disi2.nextDoc();
      index++;
    }

    IndexedDISI disi = new IndexedDISI(in, 0L, in.length(), jumpTableentryCount, denseRankPower, cardinality);
    // Advance 1 docID beyond end
    assertFalse("There should be no set bit beyond the valid docID range", disi.advanceExact(set.length()));
    disi.advance(doc); // Should be the special docID signifyin NO_MORE_DOCS from the BitSetIterator
    assertEquals("The index when advancing beyond the last defined docID should be correct",
        index, disi.index()+1); // disi.index()+1 as the while-loop also counts the NO_MORE_DOCS
  }
}
 

public BlockJoinScorer(Weight weight, Scorer childScorer, BitSet parentBits, ScoreMode scoreMode) {
  super(weight);
  //System.out.println("Q.init firstChildDoc=" + firstChildDoc);
  this.parentBits = parentBits;
  this.childScorer = childScorer;
  this.scoreMode = scoreMode;
  childTwoPhase = childScorer.twoPhaseIterator();
  if (childTwoPhase == null) {
    childApproximation = childScorer.iterator();
    parentApproximation = new ParentApproximation(childApproximation, parentBits);
    parentTwoPhase = null;
  } else {
    childApproximation = childTwoPhase.approximation();
    parentApproximation = new ParentApproximation(childTwoPhase.approximation(), parentBits);
    parentTwoPhase = new ParentTwoPhase(parentApproximation, childTwoPhase);
  }
}
 

private FieldComparator<?> getStringComparator(int numHits) {
  return new FieldComparator.TermOrdValComparator(numHits, getField(), missingValue == STRING_LAST) {

    @Override
    protected SortedDocValues getSortedDocValues(LeafReaderContext context, String field) throws IOException {
      SortedSetDocValues sortedSet = DocValues.getSortedSet(context.reader(), field);
      final BlockJoinSelector.Type type = order
          ? BlockJoinSelector.Type.MAX
          : BlockJoinSelector.Type.MIN;
      final BitSet parents = parentFilter.getBitSet(context);
      final BitSet children = childFilter.getBitSet(context);
      if (children == null) {
        return DocValues.emptySorted();
      }
      return BlockJoinSelector.wrap(sortedSet, type, parents, toIter(children));
    }

  };
}
 

private FieldComparator<?> getIntComparator(int numHits) {
  return new FieldComparator.IntComparator(numHits, getField(), (Integer) missingValue) {
    @Override
    protected NumericDocValues getNumericDocValues(LeafReaderContext context, String field) throws IOException {
      SortedNumericDocValues sortedNumeric = DocValues.getSortedNumeric(context.reader(), field);
      final BlockJoinSelector.Type type = order
          ? BlockJoinSelector.Type.MAX
          : BlockJoinSelector.Type.MIN;
      final BitSet parents = parentFilter.getBitSet(context);
      final BitSet children = childFilter.getBitSet(context);
      if (children == null) {
        return DocValues.emptyNumeric();
      }
      return BlockJoinSelector.wrap(sortedNumeric, type, parents, toIter(children));
    }
  };
}
 

private FieldComparator<?> getLongComparator(int numHits) {
  return new FieldComparator.LongComparator(numHits, getField(), (Long) missingValue) {
    @Override
    protected NumericDocValues getNumericDocValues(LeafReaderContext context, String field) throws IOException {
      SortedNumericDocValues sortedNumeric = DocValues.getSortedNumeric(context.reader(), field);
      final BlockJoinSelector.Type type = order
          ? BlockJoinSelector.Type.MAX
          : BlockJoinSelector.Type.MIN;
      final BitSet parents = parentFilter.getBitSet(context);
      final BitSet children = childFilter.getBitSet(context);
      if (children == null) {
        return DocValues.emptyNumeric();
      }
      return BlockJoinSelector.wrap(sortedNumeric, type, parents, toIter(children));
    }
  };
}
 

public void testPositionNotZero() throws IOException {
  final int BLOCKS = 10;
  final byte denseRankPower = rarely() ? -1 : (byte) (random().nextInt(7)+7); // sane + chance of disable

  BitSet set = createSetWithRandomBlocks(BLOCKS);
  try (Directory dir = newDirectory()) {
    final int cardinality = set.cardinality();
    int jumpTableEntryCount;
    try (IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT)) {
      jumpTableEntryCount = IndexedDISI.writeBitSet(new BitSetIterator(set, cardinality), out, denseRankPower);
    }
    try (IndexInput fullInput = dir.openInput("foo", IOContext.DEFAULT)) {
      IndexInput blockData =
          IndexedDISI.createBlockSlice(fullInput, "blocks", 0, fullInput.length(), jumpTableEntryCount);
      blockData.seek(random().nextInt((int) blockData.length()));

      RandomAccessInput jumpTable = IndexedDISI.createJumpTable(fullInput, 0, fullInput.length(), jumpTableEntryCount);
      IndexedDISI disi = new IndexedDISI(blockData, jumpTable, jumpTableEntryCount, denseRankPower, cardinality);
      // This failed at some point during LUCENE-8585 development as it did not reset the slice position
      disi.advanceExact(BLOCKS*65536-1);
    }
  }
}
 

private FieldComparator<?> getFloatComparator(int numHits) {
  return new FieldComparator.FloatComparator(numHits, getField(), (Float) missingValue) {
    @Override
    protected NumericDocValues getNumericDocValues(LeafReaderContext context, String field) throws IOException {
      SortedNumericDocValues sortedNumeric = DocValues.getSortedNumeric(context.reader(), field);
      final BlockJoinSelector.Type type = order
          ? BlockJoinSelector.Type.MAX
          : BlockJoinSelector.Type.MIN;
      final BitSet parents = parentFilter.getBitSet(context);
      final BitSet children = childFilter.getBitSet(context);
      if (children == null) {
        return DocValues.emptyNumeric();
      }
      return new FilterNumericDocValues(BlockJoinSelector.wrap(sortedNumeric, type, parents, toIter(children))) {
        @Override
        public long longValue() throws IOException {
          // undo the numericutils sortability
          return NumericUtils.sortableFloatBits((int) super.longValue());
        }
      };
    }
  };
}
 

private FieldComparator<?> getDoubleComparator(int numHits) {
  return new FieldComparator.DoubleComparator(numHits, getField(), (Double) missingValue) {
    @Override
    protected NumericDocValues getNumericDocValues(LeafReaderContext context, String field) throws IOException {
      SortedNumericDocValues sortedNumeric = DocValues.getSortedNumeric(context.reader(), field);
      final BlockJoinSelector.Type type = order
          ? BlockJoinSelector.Type.MAX
          : BlockJoinSelector.Type.MIN;
      final BitSet parents = parentFilter.getBitSet(context);
      final BitSet children = childFilter.getBitSet(context);
      if (children == null) {
        return DocValues.emptyNumeric();
      }
      return new FilterNumericDocValues(BlockJoinSelector.wrap(sortedNumeric, type, parents, toIter(children))) {
        @Override
        public long longValue() throws IOException {
          // undo the numericutils sortability
          return NumericUtils.sortableDoubleBits(super.longValue());
        }
      };
    }
  };
}
 

@Override
public Scorer scorer(LeafReaderContext readerContext) throws IOException {

  final Scorer parentScorer = in.scorer(readerContext);

  if (parentScorer == null) {
    // No matches
    return null;
  }

  // NOTE: this doesn't take acceptDocs into account, the responsibility
  // to not match deleted docs is on the scorer
  final BitSet parents = parentsFilter.getBitSet(readerContext);
  if (parents == null) {
    // No parents
    return null;
  }

  return new ToChildBlockJoinScorer(this, parentScorer, parents, doScores);
}
 

IncludeNestedDocsScorer(Weight weight, Scorer parentScorer, BitSet parentBits, int currentParentPointer) {
    super(weight);
    this.parentScorer = parentScorer;
    this.parentBits = parentBits;
    this.currentParentPointer = currentParentPointer;
    if (currentParentPointer == 0) {
        currentChildPointer = 0;
    } else {
        this.currentChildPointer = this.parentBits.prevSetBit(currentParentPointer - 1);
        if (currentChildPointer == -1) {
            // no previous set parent, we delete from doc 0
            currentChildPointer = 0;
        } else {
            currentChildPointer++; // we only care about children
        }
    }

    currentDoc = currentChildPointer;
}
 

@Override
public Scorer scorer(LeafReaderContext context) throws IOException {
    final Scorer parentScorer = parentWeight.scorer(context);

    // no matches
    if (parentScorer == null) {
        return null;
    }

    BitSet parents = parentsFilter.getBitSet(context);
    if (parents == null) {
        // No matches
        return null;
    }

    int firstParentDoc = parentScorer.iterator().nextDoc();
    if (firstParentDoc == DocIdSetIterator.NO_MORE_DOCS) {
        // No matches
        return null;
    }
    return new IncludeNestedDocsScorer(this, parentScorer, parents, firstParentDoc);
}
 

public void testReaderNotSuitedForCaching() throws IOException{
  Directory dir = newDirectory();
  IndexWriterConfig iwc = newIndexWriterConfig().setMergePolicy(NoMergePolicy.INSTANCE);
  RandomIndexWriter w = new RandomIndexWriter(random(), dir, iwc);
  w.addDocument(new Document());
  DirectoryReader reader = new DummyDirectoryReader(w.getReader());

  QueryBitSetProducer producer = new QueryBitSetProducer(new MatchNoDocsQuery());
  assertNull(producer.getBitSet(reader.leaves().get(0)));
  assertEquals(0, producer.cache.size());

  producer = new QueryBitSetProducer(new MatchAllDocsQuery());
  BitSet bitSet = producer.getBitSet(reader.leaves().get(0));
  assertEquals(1, bitSet.length());
  assertEquals(true, bitSet.get(0));
  assertEquals(0, producer.cache.size());

  IOUtils.close(reader, w, dir);
}
 

@Override
public Weight createWeight(IndexSearcher searcher, org.apache.lucene.search.ScoreMode scoreMode, float boost) throws IOException {
  return new ConstantScoreWeight(BitSetProducerQuery.this, boost) {
    @Override
    public Scorer scorer(LeafReaderContext context) throws IOException {
      BitSet bitSet = bitSetProducer.getBitSet(context);
      if (bitSet == null) {
        return null;
      }
      DocIdSetIterator disi = new BitSetIterator(bitSet, bitSet.approximateCardinality());
      return new ConstantScoreScorer(this, boost, scoreMode, disi);
    }

    @Override
    public boolean isCacheable(LeafReaderContext ctx) {
      return getCache();
    }
  };
}
 

static CodecReader wrapReader(String recoverySourceField, CodecReader reader, Supplier<Query> retainSourceQuerySupplier)
    throws IOException {
    NumericDocValues recoverySource = reader.getNumericDocValues(recoverySourceField);
    if (recoverySource == null || recoverySource.nextDoc() == DocIdSetIterator.NO_MORE_DOCS) {
        return reader; // early terminate - nothing to do here since non of the docs has a recovery source anymore.
    }
    IndexSearcher s = new IndexSearcher(reader);
    s.setQueryCache(null);
    Weight weight = s.createWeight(s.rewrite(retainSourceQuerySupplier.get()), ScoreMode.COMPLETE_NO_SCORES, 1.0f);
    Scorer scorer = weight.scorer(reader.getContext());
    if (scorer != null) {
        BitSet recoverySourceToKeep = BitSet.of(scorer.iterator(), reader.maxDoc());
        // calculating the cardinality is significantly cheaper than skipping all bulk-merging we might do
        // if retentions are high we keep most of it
        if (recoverySourceToKeep.cardinality() == reader.maxDoc()) {
            return reader; // keep all source
        }
        return new SourcePruningFilterCodecReader(recoverySourceField, reader, recoverySourceToKeep);
    } else {
        return new SourcePruningFilterCodecReader(recoverySourceField, reader, null);
    }
}
 

/**
 * Check that the given index is good to use for block joins.
 * @throws IllegalStateException if the index does not have an appropriate structure
 */
public static void check(IndexReader reader, BitSetProducer parentsFilter) throws IOException {
  for (LeafReaderContext context : reader.leaves()) {
    if (context.reader().maxDoc() == 0) {
      continue;
    }
    final BitSet parents = parentsFilter.getBitSet(context);
    if (parents == null || parents.cardinality() == 0) {
      throw new IllegalStateException("Every segment should have at least one parent, but " + context.reader() + " does not have any");
    }
    if (parents.get(context.reader().maxDoc() - 1) == false) {
      throw new IllegalStateException("The last document of a segment must always be a parent, but " + context.reader() + " has a child as a last doc");
    }
    final Bits liveDocs = context.reader().getLiveDocs();
    if (liveDocs != null) {
      int prevParentDoc = -1;
      DocIdSetIterator it = new BitSetIterator(parents, 0L);
      for (int parentDoc = it.nextDoc(); parentDoc != DocIdSetIterator.NO_MORE_DOCS; parentDoc = it.nextDoc()) {
        final boolean parentIsLive = liveDocs.get(parentDoc);
        for (int child = prevParentDoc + 1; child != parentDoc; child++) {
          final boolean childIsLive = liveDocs.get(child);
          if (parentIsLive != childIsLive) {
            if (childIsLive) {
              throw new IllegalStateException("Parent doc " + parentDoc + " of segment " + context.reader() + " is live but has a deleted child document " + child);
            } else {
              throw new IllegalStateException("Parent doc " + parentDoc + " of segment " + context.reader() + " is deleted but has a live child document " + child);
            }
          }
        }
        prevParentDoc = parentDoc;
      }
    }
  }
}
 

public ToChildBlockJoinScorer(Weight weight, Scorer parentScorer, BitSet parentBits, boolean doScores) {
  super(weight);
  this.doScores = doScores;
  this.parentBits = parentBits;
  this.parentScorer = parentScorer;
  this.parentIt = parentScorer.iterator();
}
 

public void testOneDoc() throws IOException {
  int maxDoc = TestUtil.nextInt(random(), 1, 100000);
  BitSet set = new SparseFixedBitSet(maxDoc);
  set.set(random().nextInt(maxDoc));
  try (Directory dir = newDirectory()) {
    doTest(set, dir);
  }
}
 

private void doTestAllSingleJump(BitSet set, Directory dir) throws IOException {
  final int cardinality = set.cardinality();
  final byte denseRankPower = rarely() ? -1 : (byte) (random().nextInt(7)+7); // sane + chance of disable
  long length;
  int jumpTableentryCount;
  try (IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT)) {
    jumpTableentryCount = IndexedDISI.writeBitSet(new BitSetIterator(set, cardinality), out, denseRankPower);
    length = out.getFilePointer();
  }

  try (IndexInput in = dir.openInput("foo", IOContext.DEFAULT)) {
    for (int i = 0; i < set.length(); i++) {
      IndexedDISI disi = new IndexedDISI(in, 0L, length, jumpTableentryCount, denseRankPower, cardinality);
      assertEquals("The bit at " + i + " should be correct with advanceExact", set.get(i), disi.advanceExact(i));

      IndexedDISI disi2 = new IndexedDISI(in, 0L, length, jumpTableentryCount, denseRankPower, cardinality);
      disi2.advance(i);
      // Proper sanity check with jump tables as an error could make them seek backwards
      assertTrue("The docID should at least be " + i + " after advance(" + i + ") but was " + disi2.docID(),
          i <= disi2.docID());
      if (set.get(i)) {
        assertEquals("The docID should be present with advance", i, disi2.docID());
      } else {
        assertNotSame("The docID should not be present with advance", i, disi2.docID());
      }
    }
  }
}
 

@Override
public BitSet getBitSet(LeafReaderContext context) throws IOException {
    try {
        return getAndLoadIfNotPresent(query, context);
    } catch (ExecutionException e) {
        throw ExceptionsHelper.convertToElastic(e);
    }
}
 

private BitSet createSetWithRandomBlocks(int blockCount) {
  final int B = 65536;
  BitSet set = new SparseFixedBitSet(blockCount * B);
  for (int block = 0; block < blockCount; block++) {
    switch (random().nextInt(4)) {
      case 0: { // EMPTY
        break;
      }
      case 1: { // ALL
        for (int docID = block* B; docID < (block+1)* B; docID++) {
          set.set(docID);
        }
        break;
      }
      case 2: { // SPARSE ( < 4096 )
        for (int docID = block* B; docID < (block+1)* B; docID += 101) {
          set.set(docID);
        }
        break;
      }
      case 3: { // DENSE ( >= 4096 )
        for (int docID = block* B; docID < (block+1)* B; docID += 3) {
          set.set(docID);
        }
        break;
      }
      default: throw new IllegalStateException("Modulo logic error: there should only be 4 possibilities");
    }
  }
  return set;
}
 

/** Wraps the provided {@link SortedNumericDocValues} in order to only select
 *  one value per parent among its {@code children} using the configured
 *  {@code selection} type. */
public static NumericDocValues wrap(SortedNumericDocValues sortedNumerics, Type selection, BitSet parents, DocIdSetIterator children) {
  NumericDocValues values;
  switch (selection) {
    case MIN:
      values = SortedNumericSelector.wrap(sortedNumerics, SortedNumericSelector.Type.MIN, SortField.Type.LONG);
      break;
    case MAX:
      values = SortedNumericSelector.wrap(sortedNumerics, SortedNumericSelector.Type.MAX, SortField.Type.LONG);
      break;
    default:
      throw new AssertionError();
  }
  return wrap(values, selection, parents, children);
}
 

/** Wraps the provided {@link NumericDocValues}, iterating over only
 *  child documents, in order to only select one value per parent among
 *  its {@code children} using the configured {@code selection} type. */
public static NumericDocValues wrap(final NumericDocValues values, Type selection, BitSet parents, DocIdSetIterator children) {
  if (values.docID() != -1) {
    throw new IllegalArgumentException("values iterator was already consumed: values.docID=" + values.docID());
  }
  return ToParentDocValues.wrap(values,selection, parents, children);
}
 

/** Wraps the provided {@link SortedDocValues} in order to only select
 *  one value per parent among its {@code children} using the configured
 *  {@code selection} type. */
public static SortedDocValues wrap(final SortedDocValues values, Type selection, BitSet parents, DocIdSetIterator children) {
  if (values.docID() != -1) {
    throw new IllegalArgumentException("values iterator was already consumed: values.docID=" + values.docID());
  }
  return ToParentDocValues.wrap(values, selection, parents, children);
}
 

public void testSortedSelector() throws IOException {
  final BitSet parents = new FixedBitSet(20);
  parents.set(0);
  parents.set(5);
  parents.set(6);
  parents.set(10);
  parents.set(15);
  parents.set(19);

  final BitSet children = new FixedBitSet(20);
  children.set(2);
  children.set(3);
  children.set(4);
  children.set(12);
  children.set(17);

  final int[] ords = new int[20];
  Arrays.fill(ords, -1);
  ords[2] = 5;
  ords[3] = 7;
  ords[4] = 3;
  ords[12] = 10;
  ords[18] = 10;

  final SortedDocValues mins = BlockJoinSelector.wrap(DocValues.singleton(new CannedSortedDocValues(ords)), BlockJoinSelector.Type.MIN, parents, toIter(children));
  assertEquals(5, nextDoc(mins,5));
  assertEquals(3, mins.ordValue());
  assertEquals(15, nextDoc(mins,15));
  assertEquals(10, mins.ordValue());
  assertNoMoreDoc(mins, 20);

  final SortedDocValues maxs = BlockJoinSelector.wrap(DocValues.singleton(new CannedSortedDocValues(ords)), BlockJoinSelector.Type.MAX, parents, toIter(children));
  assertEquals(5, nextDoc(maxs,5));
  assertEquals(7, maxs.ordValue());
  assertEquals(15, nextDoc(maxs,15));
  assertEquals(10, maxs.ordValue());
  assertNoMoreDoc( maxs,20);
}
 

private int findRootDocumentIfNested(SearchContext context, LeafReaderContext subReaderContext, int subDocId) throws IOException {
    if (context.mapperService().hasNested()) {
        BitSet bits = context.bitsetFilterCache().getBitSetProducer(Queries.newNonNestedFilter()).getBitSet(subReaderContext);
        if (!bits.get(subDocId)) {
            return bits.nextSetBit(subDocId);
        }
    }
    return -1;
}
 

private BitSet createExpectedResult(String queryValue, boolean from, IndexReader topLevelReader, IndexIterationContext context) throws IOException {
  final Map<String, List<RandomDoc>> randomValueDocs;
  final Map<String, List<RandomDoc>> linkValueDocuments;
  if (from) {
    randomValueDocs = context.randomValueFromDocs;
    linkValueDocuments = context.toDocuments;
  } else {
    randomValueDocs = context.randomValueToDocs;
    linkValueDocuments = context.fromDocuments;
  }

  BitSet expectedResult = new FixedBitSet(topLevelReader.maxDoc());
  List<RandomDoc> matchingDocs = randomValueDocs.get(queryValue);
  if (matchingDocs == null) {
    return new FixedBitSet(topLevelReader.maxDoc());
  }

  for (RandomDoc matchingDoc : matchingDocs) {
    for (String linkValue : matchingDoc.linkValues) {
      List<RandomDoc> otherMatchingDocs = linkValueDocuments.get(linkValue);
      if (otherMatchingDocs == null) {
        continue;
      }

      for (RandomDoc otherSideDoc : otherMatchingDocs) {
        PostingsEnum postingsEnum = MultiTerms.getTermPostingsEnum(topLevelReader, "id", new BytesRef(otherSideDoc.id), 0);
        assert postingsEnum != null;
        int doc = postingsEnum.nextDoc();
        expectedResult.set(doc);
      }
    }
  }
  return expectedResult;
}
 

public void testDocsWithValue() {
  final BitSet parents = new FixedBitSet(20);
  parents.set(0);
  parents.set(5);
  parents.set(6);
  parents.set(10);
  parents.set(15);
  parents.set(19);

  final BitSet children = new FixedBitSet(20);
  children.set(2);
  children.set(3);
  children.set(4);
  children.set(12);
  children.set(17);

  final BitSet childDocsWithValue = new FixedBitSet(20);
  childDocsWithValue.set(2);
  childDocsWithValue.set(3);
  childDocsWithValue.set(4);
  childDocsWithValue.set(8);
  childDocsWithValue.set(16);

  final Bits docsWithValue = BlockJoinSelector.wrap(childDocsWithValue, parents, children);
  assertFalse(docsWithValue.get(0));
  assertTrue(docsWithValue.get(5));
  assertFalse(docsWithValue.get(6));
  assertFalse(docsWithValue.get(10));
  assertFalse(docsWithValue.get(15));
  assertFalse(docsWithValue.get(19));
}
 

private Document getParentDoc(IndexReader reader, BitSetProducer parents, int childDocID) throws IOException {
  final List<LeafReaderContext> leaves = reader.leaves();
  final int subIndex = ReaderUtil.subIndex(childDocID, leaves);
  final LeafReaderContext leaf = leaves.get(subIndex);
  final BitSet bits = parents.getBitSet(leaf);
  return leaf.reader().document(bits.nextSetBit(childDocID - leaf.docBase));
}