LUCENE-7456: PerFieldPostings/DocValuesFormat was failing to delegate the merge method

lucene/CHANGES.txt

@@ -49,6 +49,9 @@ Bug Fixes
 * LUCENE-7472: MultiFieldQueryParser.getFieldQuery() drops queries that are
   neither BooleanQuery nor TermQuery.  (Steve Rowe)
 
+* LUCENE-7456: PerFieldPostings/DocValues was failing to delegate the
+  merge method (Julien MASSENET via Mike McCandless)
+
 Improvements
 
 * LUCENE-7439: FuzzyQuery now matches all terms within the specified

lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldDocValuesFormat.java

@@ -18,6 +18,7 @@ package org.apache.lucene.codecs.perfield;
 
 import java.io.Closeable;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.IdentityHashMap;
@@ -32,6 +33,7 @@ import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.DocValuesType;
 import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.MergeState;
 import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
@@ -127,6 +129,32 @@ public abstract class PerFieldDocValuesFormat extends DocValuesFormat {
       getInstance(field).addSortedSetField(field, valuesProducer);
     }
 
+    @Override
+    public void merge(MergeState mergeState) throws IOException {
+      Map<DocValuesConsumer, Collection<String>> consumersToField = new IdentityHashMap<>();
+
+      // Group each consumer by the fields it handles
+      for (FieldInfo fi : mergeState.mergeFieldInfos) {
+        DocValuesConsumer consumer = getInstance(fi);
+        Collection<String> fieldsForConsumer = consumersToField.get(consumer);
+        if (fieldsForConsumer == null) {
+          fieldsForConsumer = new ArrayList<>();
+          consumersToField.put(consumer, fieldsForConsumer);
+        }
+        fieldsForConsumer.add(fi.name);
+      }
+
+      // Delegate the merge to the appropriate consumer
+      PerFieldMergeState pfMergeState = new PerFieldMergeState(mergeState);
+      try {
+        for (Map.Entry<DocValuesConsumer, Collection<String>> e : consumersToField.entrySet()) {
+          e.getKey().merge(pfMergeState.apply(e.getValue()));
+        }
+      } finally {
+        pfMergeState.reset();
+      }
+    }
+
     private DocValuesConsumer getInstance(FieldInfo field) throws IOException {
       DocValuesFormat format = null;
       if (field.getDocValuesGen() != -1) {

lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldMergeState.java

@@ -0,0 +1,274 @@
+/*
+ * 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.
+ */
+package org.apache.lucene.codecs.perfield;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.index.DocValuesType;
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.FieldInfos;
+import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.MergeState;
+import org.apache.lucene.index.Terms;
+
+/**
+ * Utility class to update the {@link MergeState} instance to be restricted to a set of fields.
+ * <p>
+ * Warning: the input {@linkplain MergeState} instance will be updated when calling {@link #apply(Collection)}.
+ * <p>
+ * It should be called within a {@code try &#123;...&#125; finally &#123;...&#125;} block to make sure that the mergeState instance is
+ * restored to its original state:
+ * <pre>
+ * PerFieldMergeState pfMergeState = new PerFieldMergeState(mergeState);
+ * try {
+ *   doSomething(pfMergeState.apply(fields));
+ *   ...
+ * } finally {
+ *   pfMergeState.reset();
+ * }
+ * </pre>
+ */
+final class PerFieldMergeState {
+  private final MergeState in;
+  private final FieldInfos orgMergeFieldInfos;
+  private final FieldInfos[] orgFieldInfos;
+  private final FieldsProducer[] orgFieldsProducers;
+
+  PerFieldMergeState(MergeState in) {
+    this.in = in;
+    this.orgMergeFieldInfos = in.mergeFieldInfos;
+    this.orgFieldInfos = new FieldInfos[in.fieldInfos.length];
+    this.orgFieldsProducers = new FieldsProducer[in.fieldsProducers.length];
+
+    System.arraycopy(in.fieldInfos, 0, this.orgFieldInfos, 0, this.orgFieldInfos.length);
+    System.arraycopy(in.fieldsProducers, 0, this.orgFieldsProducers, 0, this.orgFieldsProducers.length);
+  }
+
+  /**
+   * Update the input {@link MergeState} instance to restrict the fields to the given ones.
+   *
+   * @param fields The fields to keep in the updated instance.
+   * @return The updated instance.
+   */
+  MergeState apply(Collection<String> fields) {
+    in.mergeFieldInfos = new FilterFieldInfos(orgMergeFieldInfos, fields);
+    for (int i = 0; i < orgFieldInfos.length; i++) {
+      in.fieldInfos[i] = new FilterFieldInfos(orgFieldInfos[i], fields);
+    }
+    for (int i = 0; i < orgFieldsProducers.length; i++) {
+      in.fieldsProducers[i] = new FilterFieldsProducer(orgFieldsProducers[i], fields);
+    }
+    return in;
+  }
+
+  /**
+   * Resets the input {@link MergeState} instance to its original state.
+   *
+   * @return The reset instance.
+   */
+  MergeState reset() {
+    in.mergeFieldInfos = orgMergeFieldInfos;
+    System.arraycopy(orgFieldInfos, 0, in.fieldInfos, 0, in.fieldInfos.length);
+    System.arraycopy(orgFieldsProducers, 0, in.fieldsProducers, 0, in.fieldsProducers.length);
+    return in;
+  }
+
+  private static class FilterFieldInfos extends FieldInfos {
+    private final Set<String> filteredNames;
+    private final List<FieldInfo> filtered;
+
+    // Copy of the private fields from FieldInfos
+    // Renamed so as to be less confusing about which fields we're referring to
+    private final boolean filteredHasVectors;
+    private final boolean filteredHasProx;
+    private final boolean filteredHasPayloads;
+    private final boolean filteredHasOffsets;
+    private final boolean filteredHasFreq;
+    private final boolean filteredHasNorms;
+    private final boolean filteredHasDocValues;
+    private final boolean filteredHasPointValues;
+
+    FilterFieldInfos(FieldInfos src, Collection<String> filterFields) {
+      // Copy all the input FieldInfo objects since the field numbering must be kept consistent
+      super(toArray(src));
+
+      boolean hasVectors = false;
+      boolean hasProx = false;
+      boolean hasPayloads = false;
+      boolean hasOffsets = false;
+      boolean hasFreq = false;
+      boolean hasNorms = false;
+      boolean hasDocValues = false;
+      boolean hasPointValues = false;
+
+      this.filteredNames = new HashSet<>(filterFields);
+      this.filtered = new ArrayList<>(filterFields.size());
+      for (FieldInfo fi : src) {
+        if (filterFields.contains(fi.name)) {
+          this.filtered.add(fi);
+          hasVectors |= fi.hasVectors();
+          hasProx |= fi.getIndexOptions().compareTo(IndexOptions.DOCS_AND_FREQS_AND_POSITIONS) >= 0;
+          hasFreq |= fi.getIndexOptions() != IndexOptions.DOCS;
+          hasOffsets |= fi.getIndexOptions().compareTo(IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS) >= 0;
+          hasNorms |= fi.hasNorms();
+          hasDocValues |= fi.getDocValuesType() != DocValuesType.NONE;
+          hasPayloads |= fi.hasPayloads();
+          hasPointValues |= (fi.getPointDimensionCount() != 0);
+        }
+      }
+
+      this.filteredHasVectors = hasVectors;
+      this.filteredHasProx = hasProx;
+      this.filteredHasPayloads = hasPayloads;
+      this.filteredHasOffsets = hasOffsets;
+      this.filteredHasFreq = hasFreq;
+      this.filteredHasNorms = hasNorms;
+      this.filteredHasDocValues = hasDocValues;
+      this.filteredHasPointValues = hasPointValues;
+    }
+
+    private static FieldInfo[] toArray(FieldInfos src) {
+      FieldInfo[] res = new FieldInfo[src.size()];
+      int i = 0;
+      for (FieldInfo fi : src) {
+        res[i++] = fi;
+      }
+      return res;
+    }
+
+    @Override
+    public Iterator<FieldInfo> iterator() {
+      return filtered.iterator();
+    }
+
+    @Override
+    public boolean hasFreq() {
+      return filteredHasFreq;
+    }
+
+    @Override
+    public boolean hasProx() {
+      return filteredHasProx;
+    }
+
+    @Override
+    public boolean hasPayloads() {
+      return filteredHasPayloads;
+    }
+
+    @Override
+    public boolean hasOffsets() {
+      return filteredHasOffsets;
+    }
+
+    @Override
+    public boolean hasVectors() {
+      return filteredHasVectors;
+    }
+
+    @Override
+    public boolean hasNorms() {
+      return filteredHasNorms;
+    }
+
+    @Override
+    public boolean hasDocValues() {
+      return filteredHasDocValues;
+    }
+
+    @Override
+    public boolean hasPointValues() {
+      return filteredHasPointValues;
+    }
+
+    @Override
+    public int size() {
+      return filtered.size();
+    }
+
+    @Override
+    public FieldInfo fieldInfo(String fieldName) {
+      if (!filteredNames.contains(fieldName)) {
+        // Throw IAE to be consistent with fieldInfo(int) which throws it as well on invalid numbers
+        throw new IllegalArgumentException("The field named '" + fieldName + "' is not accessible in the current " +
+            "merge context, available ones are: " + filteredNames);
+      }
+      return super.fieldInfo(fieldName);
+    }
+
+    @Override
+    public FieldInfo fieldInfo(int fieldNumber) {
+      FieldInfo res = super.fieldInfo(fieldNumber);
+      if (!filteredNames.contains(res.name)) {
+        throw new IllegalArgumentException("The field named '" + res.name + "' numbered '" + fieldNumber + "' is not " +
+            "accessible in the current merge context, available ones are: " + filteredNames);
+      }
+      return res;
+    }
+  }
+
+  private static class FilterFieldsProducer extends FieldsProducer {
+    private final FieldsProducer in;
+    private final List<String> filtered;
+
+    FilterFieldsProducer(FieldsProducer in, Collection<String> filterFields) {
+      this.in = in;
+      this.filtered = new ArrayList<>(filterFields);
+    }
+
+    @Override
+    public long ramBytesUsed() {
+      return in.ramBytesUsed();
+    }
+
+    @Override
+    public Iterator<String> iterator() {
+      return filtered.iterator();
+    }
+
+    @Override
+    public Terms terms(String field) throws IOException {
+      if (!filtered.contains(field)) {
+        throw new IllegalArgumentException("The field named '" + field + "' is not accessible in the current " +
+            "merge context, available ones are: " + filtered);
+      }
+      return in.terms(field);
+    }
+
+    @Override
+    public int size() {
+      return filtered.size();
+    }
+
+    @Override
+    public void close() throws IOException {
+      in.close();
+    }
+
+    @Override
+    public void checkIntegrity() throws IOException {
+      in.checkIntegrity();
+    }
+  }
+}

lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldPostingsFormat.java

@@ -39,6 +39,8 @@ import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.FilterLeafReader.FilterFields;
 import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.MergeState;
+import org.apache.lucene.index.MultiFields;
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.index.Terms;
@@ -116,7 +118,61 @@ public abstract class PerFieldPostingsFormat extends PostingsFormat {
 
     @Override
     public void write(Fields fields) throws IOException {
+      Map<PostingsFormat, FieldsGroup> formatToGroups = buildFieldsGroupMapping(fields);
 
+      // Write postings
+      boolean success = false;
+      try {
+        for (Map.Entry<PostingsFormat, FieldsGroup> ent : formatToGroups.entrySet()) {
+          PostingsFormat format = ent.getKey();
+          final FieldsGroup group = ent.getValue();
+
+          // Exposes only the fields from this group:
+          Fields maskedFields = new FilterFields(fields) {
+            @Override
+            public Iterator<String> iterator() {
+              return group.fields.iterator();
+            }
+          };
+
+          FieldsConsumer consumer = format.fieldsConsumer(group.state);
+          toClose.add(consumer);
+          consumer.write(maskedFields);
+        }
+        success = true;
+      } finally {
+        if (!success) {
+          IOUtils.closeWhileHandlingException(toClose);
+        }
+      }
+    }
+
+    @Override
+    public void merge(MergeState mergeState) throws IOException {
+      Map<PostingsFormat, FieldsGroup> formatToGroups = buildFieldsGroupMapping(new MultiFields(mergeState.fieldsProducers, null));
+
+      // Merge postings
+      PerFieldMergeState pfMergeState = new PerFieldMergeState(mergeState);
+      boolean success = false;
+      try {
+        for (Map.Entry<PostingsFormat, FieldsGroup> ent : formatToGroups.entrySet()) {
+          PostingsFormat format = ent.getKey();
+          final FieldsGroup group = ent.getValue();
+
+          FieldsConsumer consumer = format.fieldsConsumer(group.state);
+          toClose.add(consumer);
+          consumer.merge(pfMergeState.apply(group.fields));
+        }
+        success = true;
+      } finally {
+        pfMergeState.reset();
+        if (!success) {
+          IOUtils.closeWhileHandlingException(toClose);
+        }
+      }
+    }
+
+    private Map<PostingsFormat, FieldsGroup> buildFieldsGroupMapping(Fields fields) {
       // Maps a PostingsFormat instance to the suffix it
       // should use
       Map<PostingsFormat,FieldsGroup> formatToGroups = new HashMap<>();
@@ -124,7 +180,7 @@ public abstract class PerFieldPostingsFormat extends PostingsFormat {
       // Holds last suffix of each PostingFormat name
       Map<String,Integer> suffixes = new HashMap<>();
 
-      // First pass: assign field -> PostingsFormat
+      // Assign field -> PostingsFormat
       for(String field : fields) {
         FieldInfo fieldInfo = writeState.fieldInfos.fieldInfo(field);
 
@@ -177,32 +233,7 @@ public abstract class PerFieldPostingsFormat extends PostingsFormat {
                                           ", field=" + fieldInfo.name + ", old=" + previousValue + ", new=" + group.suffix);
         }
       }
-
+      return formatToGroups;
-      // Second pass: write postings
-      boolean success = false;
-      try {
-        for(Map.Entry<PostingsFormat,FieldsGroup> ent : formatToGroups.entrySet()) {
-          PostingsFormat format = ent.getKey();
-          final FieldsGroup group = ent.getValue();
-
-          // Exposes only the fields from this group:
-          Fields maskedFields = new FilterFields(fields) {
-              @Override
-              public Iterator<String> iterator() {
-                return group.fields.iterator();
-              }
-            };
-
-          FieldsConsumer consumer = format.fieldsConsumer(group.state);
-          toClose.add(consumer);
-          consumer.write(maskedFields);
-        }
-        success = true;
-      } finally {
-        if (success == false) {
-          IOUtils.closeWhileHandlingException(toClose);
-        }
-      }
     }
 
     @Override

lucene/core/src/test/org/apache/lucene/codecs/perfield/TestPerFieldDocValuesFormat.java

@@ -18,13 +18,19 @@ package org.apache.lucene.codecs.perfield;
 
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
 import java.util.Random;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.DocValuesConsumer;
 import org.apache.lucene.codecs.DocValuesFormat;
+import org.apache.lucene.codecs.DocValuesProducer;
 import org.apache.lucene.codecs.asserting.AssertingCodec;
 import org.apache.lucene.document.BinaryDocValuesField;
 import org.apache.lucene.document.Document;
@@ -33,11 +39,15 @@ import org.apache.lucene.document.NumericDocValuesField;
 import org.apache.lucene.index.BaseDocValuesFormatTestCase;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.MergeState;
 import org.apache.lucene.index.NumericDocValues;
 import org.apache.lucene.index.RandomCodec;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.Query;
@@ -127,4 +137,116 @@ public class TestPerFieldDocValuesFormat extends BaseDocValuesFormatTestCase {
     ireader.close();
     directory.close();
   }
+
+  public void testMergeCalledOnTwoFormats() throws IOException {
+    MergeRecordingDocValueFormatWrapper dvf1 = new MergeRecordingDocValueFormatWrapper(TestUtil.getDefaultDocValuesFormat());
+    MergeRecordingDocValueFormatWrapper dvf2 = new MergeRecordingDocValueFormatWrapper(TestUtil.getDefaultDocValuesFormat());
+
+    IndexWriterConfig iwc = newIndexWriterConfig();
+    iwc.setCodec(new AssertingCodec() {
+      @Override
+      public DocValuesFormat getDocValuesFormatForField(String field) {
+        switch (field) {
+          case "dv1":
+          case "dv2":
+            return dvf1;
+
+          case "dv3":
+            return dvf2;
+
+          default:
+            return super.getDocValuesFormatForField(field);
+        }
+      }
+    });
+
+    Directory directory = newDirectory();
+
+    IndexWriter iwriter = new IndexWriter(directory, iwc);
+
+    Document doc = new Document();
+    doc.add(new NumericDocValuesField("dv1", 5));
+    doc.add(new NumericDocValuesField("dv2", 42));
+    doc.add(new BinaryDocValuesField("dv3", new BytesRef("hello world")));
+    iwriter.addDocument(doc);
+    iwriter.commit();
+
+    doc = new Document();
+    doc.add(new NumericDocValuesField("dv1", 8));
+    doc.add(new NumericDocValuesField("dv2", 45));
+    doc.add(new BinaryDocValuesField("dv3", new BytesRef("goodbye world")));
+    iwriter.addDocument(doc);
+    iwriter.commit();
+
+    iwriter.forceMerge(1, true);
+    iwriter.close();
+
+    assertEquals(1, dvf1.nbMergeCalls);
+    assertEquals(new HashSet<>(Arrays.asList("dv1", "dv2")), new HashSet<>(dvf1.fieldNames));
+    assertEquals(1, dvf2.nbMergeCalls);
+    assertEquals(Collections.singletonList("dv3"), dvf2.fieldNames);
+
+    directory.close();
+  }
+
+  private static final class MergeRecordingDocValueFormatWrapper extends DocValuesFormat {
+    private final DocValuesFormat delegate;
+    final List<String> fieldNames = new ArrayList<>();
+    volatile int nbMergeCalls = 0;
+
+    MergeRecordingDocValueFormatWrapper(DocValuesFormat delegate) {
+      super(delegate.getName());
+      this.delegate = delegate;
+    }
+
+    @Override
+    public DocValuesConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
+      final DocValuesConsumer consumer = delegate.fieldsConsumer(state);
+      return new DocValuesConsumer() {
+        @Override
+        public void addNumericField(FieldInfo field, Iterable<Number> values) throws IOException {
+          consumer.addNumericField(field, values);
+        }
+
+        @Override
+        public void addBinaryField(FieldInfo field, Iterable<BytesRef> values) throws IOException {
+          consumer.addBinaryField(field, values);
+        }
+
+        @Override
+        public void addSortedField(FieldInfo field, Iterable<BytesRef> values, Iterable<Number> docToOrd) throws IOException {
+          consumer.addSortedField(field, values, docToOrd);
+        }
+
+        @Override
+        public void addSortedNumericField(FieldInfo field, Iterable<Number> docToValueCount, Iterable<Number> values) throws IOException {
+          consumer.addSortedNumericField(field, docToValueCount, values);
+        }
+
+        @Override
+        public void addSortedSetField(FieldInfo field, Iterable<BytesRef> values, Iterable<Number> docToOrdCount, Iterable<Number> ords) throws IOException {
+          consumer.addSortedSetField(field, values, docToOrdCount, ords);
+        }
+
+        @Override
+        public void merge(MergeState mergeState) throws IOException {
+          nbMergeCalls++;
+          for (FieldInfo fi : mergeState.mergeFieldInfos) {
+            fieldNames.add(fi.name);
+          }
+          consumer.merge(mergeState);
+        }
+
+        @Override
+        public void close() throws IOException {
+          consumer.close();
+        }
+      };
+    }
+
+    @Override
+    public DocValuesProducer fieldsProducer(SegmentReadState state) throws IOException {
+      return delegate.fieldsProducer(state);
+    }
+  }
 }

lucene/core/src/test/org/apache/lucene/codecs/perfield/TestPerFieldPostingsFormat2.java

@@ -18,9 +18,16 @@ package org.apache.lucene.codecs.perfield;
 
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
 
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.FieldsConsumer;
+import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.asserting.AssertingCodec;
 import org.apache.lucene.codecs.blockterms.LuceneVarGapFixedInterval;
@@ -29,14 +36,21 @@ import org.apache.lucene.codecs.memory.MemoryPostingsFormat;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.FieldType;
+import org.apache.lucene.document.IntPoint;
+import org.apache.lucene.document.StringField;
 import org.apache.lucene.document.TextField;
 import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.LogDocMergePolicy;
+import org.apache.lucene.index.MergeState;
 import org.apache.lucene.index.RandomIndexWriter;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.TermQuery;
@@ -322,4 +336,100 @@ public class TestPerFieldPostingsFormat2 extends LuceneTestCase {
     iw.close();
     dir.close(); // checkindex
   }
+
+  @SuppressWarnings("deprecation")
+  public void testMergeCalledOnTwoFormats() throws IOException {
+    MergeRecordingPostingsFormatWrapper pf1 = new MergeRecordingPostingsFormatWrapper(TestUtil.getDefaultPostingsFormat());
+    MergeRecordingPostingsFormatWrapper pf2 = new MergeRecordingPostingsFormatWrapper(TestUtil.getDefaultPostingsFormat());
+
+    IndexWriterConfig iwc = newIndexWriterConfig();
+    iwc.setCodec(new AssertingCodec() {
+      @Override
+      public PostingsFormat getPostingsFormatForField(String field) {
+        switch (field) {
+          case "f1":
+          case "f2":
+            return pf1;
+
+          case "f3":
+          case "f4":
+            return pf2;
+
+          default:
+            return super.getPostingsFormatForField(field);
+        }
+      }
+    });
+
+    Directory directory = newDirectory();
+
+    IndexWriter iwriter = new IndexWriter(directory, iwc);
+
+    Document doc = new Document();
+    doc.add(new StringField("f1", "val1", Field.Store.NO));
+    doc.add(new StringField("f2", "val2", Field.Store.YES));
+    doc.add(new IntPoint("f3", 3)); // Points are not indexed as postings and should not appear in the merge fields
+    doc.add(new StringField("f4", "val4", Field.Store.NO));
+    iwriter.addDocument(doc);
+    iwriter.commit();
+
+    doc = new Document();
+    doc.add(new StringField("f1", "val5", Field.Store.NO));
+    doc.add(new StringField("f2", "val6", Field.Store.YES));
+    doc.add(new IntPoint("f3", 7));
+    doc.add(new StringField("f4", "val8", Field.Store.NO));
+    iwriter.addDocument(doc);
+    iwriter.commit();
+
+    iwriter.forceMerge(1, true);
+    iwriter.close();
+
+    assertEquals(1, pf1.nbMergeCalls);
+    assertEquals(new HashSet<>(Arrays.asList("f1", "f2")), new HashSet<>(pf1.fieldNames));
+    assertEquals(1, pf2.nbMergeCalls);
+    assertEquals(Collections.singletonList("f4"), pf2.fieldNames);
+
+    directory.close();
+  }
+
+  private static final class MergeRecordingPostingsFormatWrapper extends PostingsFormat {
+    private final PostingsFormat delegate;
+    final List<String> fieldNames = new ArrayList<>();
+    int nbMergeCalls = 0;
+
+    MergeRecordingPostingsFormatWrapper(PostingsFormat delegate) {
+      super(delegate.getName());
+      this.delegate = delegate;
+    }
+
+    @Override
+    public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
+      final FieldsConsumer consumer = delegate.fieldsConsumer(state);
+      return new FieldsConsumer() {
+        @Override
+        public void write(Fields fields) throws IOException {
+          consumer.write(fields);
+        }
+
+        @Override
+        public void merge(MergeState mergeState) throws IOException {
+          nbMergeCalls++;
+          for (FieldInfo fi : mergeState.mergeFieldInfos) {
+            fieldNames.add(fi.name);
+          }
+          consumer.merge(mergeState);
+        }
+
+        @Override
+        public void close() throws IOException {
+          consumer.close();
+        }
+      };
+    }
+
+    @Override
+    public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
+      return delegate.fieldsProducer(state);
+    }
+  }
 }