diff --git a/java/execution/impl/src/com/intellij/execution/testDiscovery/indices/TestFilesIndex.java b/java/execution/impl/src/com/intellij/execution/testDiscovery/indices/TestFilesIndex.java
index ad96c0b44db2..8158d3d34cfe 100644
--- a/java/execution/impl/src/com/intellij/execution/testDiscovery/indices/TestFilesIndex.java
+++ b/java/execution/impl/src/com/intellij/execution/testDiscovery/indices/TestFilesIndex.java
@@ -38,7 +38,7 @@ public class TestFilesIndex extends MapReduceIndex<Integer, Void, UsedSources> {
   @Nullable
   Collection<Integer> getTestDataFor(int testId) throws IOException {
     ForwardIndex forwardIndex = getForwardIndexMap();
-    KeyCollectionForwardIndexAccessor<Integer, Void, UsedSources> forwardIndexAccessor = (KeyCollectionForwardIndexAccessor<Integer, Void, UsedSources>)getForwardIndexAccessor();
+    KeyCollectionForwardIndexAccessor<Integer, Void> forwardIndexAccessor = (KeyCollectionForwardIndexAccessor<Integer, Void>)getForwardIndexAccessor();
     return forwardIndexAccessor.deserializeData(forwardIndex.get(testId));
   }
 
diff --git a/platform/lang-impl/src/com/intellij/psi/stubs/StubUpdatingForwardIndexAccessor.java b/platform/lang-impl/src/com/intellij/psi/stubs/StubUpdatingForwardIndexAccessor.java
index d3cbf854301a..be57c5c9296a 100644
--- a/platform/lang-impl/src/com/intellij/psi/stubs/StubUpdatingForwardIndexAccessor.java
+++ b/platform/lang-impl/src/com/intellij/psi/stubs/StubUpdatingForwardIndexAccessor.java
@@ -5,6 +5,7 @@ import com.intellij.openapi.progress.ProgressManager;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.indexing.FileContent;
 import com.intellij.util.indexing.ID;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
 import com.intellij.util.indexing.impl.forward.AbstractForwardIndexAccessor;
 import com.intellij.util.io.DataExternalizer;
@@ -19,7 +20,7 @@ import java.io.IOException;
 import java.util.Collections;
 import java.util.Map;
 
-class StubUpdatingForwardIndexAccessor extends AbstractForwardIndexAccessor<Integer, SerializedStubTree, IndexedStubs , FileContent> {
+class StubUpdatingForwardIndexAccessor extends AbstractForwardIndexAccessor<Integer, SerializedStubTree, IndexedStubs> {
   StubUpdatingForwardIndexAccessor() {super(new DataExternalizer<IndexedStubs>() {
     private volatile boolean myEnsuredStubElementTypesLoaded;
 
@@ -68,10 +69,10 @@ class StubUpdatingForwardIndexAccessor extends AbstractForwardIndexAccessor<Inte
     }
   });}
 
+  @Nullable
   @Override
-  public IndexedStubs convertToDataType(@Nullable Map<Integer, SerializedStubTree> map,
-                                                                      @Nullable FileContent content) {
-    return getIndexedStubs(map);
+  public IndexedStubs convertToDataType(@NotNull InputData<Integer, SerializedStubTree> data) {
+    return getIndexedStubs(data.getKeyValues());
   }
 
   @Override
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/HashIdForwardIndexAccessor.java b/platform/lang-impl/src/com/intellij/util/indexing/HashIdForwardIndexAccessor.java
index ccad9895626b..0b97d75a0f57 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/HashIdForwardIndexAccessor.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/HashIdForwardIndexAccessor.java
@@ -1,6 +1,7 @@
 // Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.util.indexing;
 
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
 import com.intellij.util.indexing.impl.MapInputDataDiffBuilder;
 import com.intellij.util.indexing.impl.forward.AbstractMapForwardIndexAccessor;
@@ -13,8 +14,8 @@ import java.io.IOException;
 import java.util.Map;
 
 class HashIdForwardIndexAccessor<Key, Value, Input>
-  extends AbstractMapForwardIndexAccessor<Key, Value, Integer, Input>
-  implements IntForwardIndexAccessor<Key, Value, Input> {
+  extends AbstractMapForwardIndexAccessor<Key, Value, Integer>
+  implements IntForwardIndexAccessor<Key, Value> {
   private final UpdatableSnapshotInputMappingIndex<Key, Value, Input> mySnapshotInputMappingIndex;
 
   HashIdForwardIndexAccessor(@NotNull UpdatableSnapshotInputMappingIndex<Key, Value, Input> snapshotInputMappingIndex) {
@@ -35,12 +36,13 @@ class HashIdForwardIndexAccessor<Key, Value, Input>
   }
 
   @Override
-  public int convertToInt(@Nullable Map<Key, Value> map, @Nullable Input content) {
-    try {
-      return mySnapshotInputMappingIndex.getHashId(content);
-    }
-    catch (IOException e) {
-      throw new RuntimeException(e);
-    }
+  public int serializeIndexedDataToInt(@NotNull InputData<Key, Value> data) {
+    return data == InputData.empty() ? 0 : ((HashedInputData)data).getHashId();
+  }
+
+  @Nullable
+  @Override
+  public Integer convertToDataType(@NotNull InputData<Key, Value> data) {
+    return serializeIndexedDataToInt(data);
   }
 }
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/HashedInputData.java b/platform/lang-impl/src/com/intellij/util/indexing/HashedInputData.java
new file mode 100644
index 000000000000..017f4d824268
--- /dev/null
+++ b/platform/lang-impl/src/com/intellij/util/indexing/HashedInputData.java
@@ -0,0 +1,20 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.util.indexing;
+
+import com.intellij.util.indexing.impl.InputData;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Map;
+
+public class HashedInputData<Key, Value> extends InputData<Key, Value> {
+  private final int myHashId;
+
+  protected HashedInputData(@NotNull Map<Key, Value> values, int hashId) {
+    super(values);
+    myHashId = hashId;
+  }
+
+  public int getHashId() {
+    return myHashId;
+  }
+}
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/SharedMapForwardIndex.java b/platform/lang-impl/src/com/intellij/util/indexing/SharedMapForwardIndex.java
index 4264e2da4149..2bad7017ab12 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/SharedMapForwardIndex.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/SharedMapForwardIndex.java
@@ -26,10 +26,10 @@ public class SharedMapForwardIndex implements ForwardIndex {
 
   // only verification purpose
   @Nullable
-  private final AbstractForwardIndexAccessor<?, ?, ?, ?> myAccessor;
+  private final AbstractForwardIndexAccessor<?, ?, ?> myAccessor;
 
   public SharedMapForwardIndex(@NotNull IndexExtension<?, ?, ?> extension,
-                               @Nullable AbstractForwardIndexAccessor<?, ?, ?, ?> accessor,
+                               @Nullable AbstractForwardIndexAccessor<?, ?, ?> accessor,
                                @Nullable File verificationIndexStorageFile,
                                boolean verificationIndexHasChunks) throws IOException {
     myIndexId = (ID<?, ?>)extension.getName();
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappingIndex.java b/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappingIndex.java
index a72497ac243a..52c3575e4391 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappingIndex.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappingIndex.java
@@ -1,6 +1,7 @@
 // Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.util.indexing;
 
+import com.intellij.util.indexing.impl.InputData;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -12,5 +13,5 @@ import java.util.Map;
 @ApiStatus.Experimental
 public interface SnapshotInputMappingIndex<Key, Value, Input> extends Closeable {
   @Nullable
-  Map<Key, Value> readData(@NotNull Input content) throws IOException;
+  InputData<Key, Value> readData(@NotNull Input content) throws IOException;
 }
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappings.java b/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappings.java
index 2962d50957ce..e0ebd2ed7634 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappings.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/SnapshotInputMappings.java
@@ -13,6 +13,7 @@ import com.intellij.util.CompressionUtil;
 import com.intellij.util.ExceptionUtil;
 import com.intellij.util.SystemProperties;
 import com.intellij.util.indexing.impl.DebugAssertions;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.forward.AbstractForwardIndexAccessor;
 import com.intellij.util.indexing.impl.forward.PersistentMapBasedForwardIndex;
 import com.intellij.util.io.*;
@@ -70,12 +71,13 @@ class SnapshotInputMappings<Key, Value, Input> implements UpdatableSnapshotInput
 
   @Nullable
   @Override
-  public Map<Key, Value> readData(@NotNull Input content) throws IOException {
+  public InputData<Key, Value> readData(@NotNull Input content) throws IOException {
     Map<Key, Value> data = null;
+    int hashId = 0;
 
     if (doReadSavedPersistentData) {
       if (myContents == null || !myContents.isBusyReading() || DebugAssertions.EXTRA_SANITY_CHECKS) { // avoid blocking read, we can calculate index value
-        int hashId = getHashId(content);
+        hashId = getHashId(content);
         ByteArraySequence bytes = readContents(hashId);
 
         if (bytes != null) {
@@ -96,25 +98,32 @@ class SnapshotInputMappings<Key, Value, Input> implements UpdatableSnapshotInput
         }
       }
     }
-    return data;
+    return data == null ? null : new HashedInputData<>(data, hashId);
   }
 
   @Override
-  public void putData(@Nullable Input content, @NotNull Map<Key, Value> data) throws IOException {
-    int hashId = getHashId(content);
-    boolean saved = savePersistentData(data, hashId);
+  public InputData<Key, Value> putData(@Nullable Input content, @NotNull InputData<Key, Value> data) throws IOException {
+    int hashId;
+    InputData<Key, Value> result;
+    if (data instanceof HashedInputData) {
+      hashId = ((HashedInputData<Key, Value>)data).getHashId();
+      result = data;
+    } else {
+      hashId = getHashId(content);
+      result = hashId == 0 ? InputData.empty() : new HashedInputData<>(data.getKeyValues(), hashId);
+    }
+    boolean saved = savePersistentData(data.getKeyValues(), hashId);
     if (DebugAssertions.EXTRA_SANITY_CHECKS) {
       if (saved) {
         try {
-          myIndexingTrace.put(hashId, getContentDebugData(content) +
-                                      "," +
-                                      ExceptionUtil.getThrowableText(new Throwable()));
+          myIndexingTrace.put(hashId, getContentDebugData(content) + "," + ExceptionUtil.getThrowableText(new Throwable()));
         }
         catch (IOException ex) {
           LOG.error(ex);
         }
       }
     }
+    return result;
   }
 
   @NotNull
@@ -123,8 +132,7 @@ class SnapshotInputMappings<Key, Value, Input> implements UpdatableSnapshotInput
     return "[" + content.getFile().getPath() + ";" + content.getFileType().getName() + ";" + content.getCharset() + "]";
   }
 
-  @Override
-  public int getHashId(@Nullable Input content) throws IOException {
+  private int getHashId(@Nullable Input content) throws IOException {
     return content == null ? 0 : getHashOfContent((FileContent) content);
   }
 
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/UpdatableSnapshotInputMappingIndex.java b/platform/lang-impl/src/com/intellij/util/indexing/UpdatableSnapshotInputMappingIndex.java
index 26176227537d..b9a467618a98 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/UpdatableSnapshotInputMappingIndex.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/UpdatableSnapshotInputMappingIndex.java
@@ -1,6 +1,7 @@
 // Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.util.indexing;
 
+import com.intellij.util.indexing.impl.InputData;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -13,9 +14,7 @@ public interface UpdatableSnapshotInputMappingIndex<Key, Value, Input> extends S
   @NotNull
   Map<Key, Value> readData(int hashId) throws IOException;
 
-  void putData(@NotNull Input content, @NotNull Map<Key, Value> data) throws IOException;
-
-  int getHashId(@Nullable Input content) throws IOException;
+  InputData<Key, Value> putData(@NotNull Input content, @NotNull InputData<Key, Value> data) throws IOException;
 
   void flush() throws IOException;
 
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/VfsAwareMapReduceIndex.java b/platform/lang-impl/src/com/intellij/util/indexing/VfsAwareMapReduceIndex.java
index 13601fb70ff7..a40b0f3abb1f 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/VfsAwareMapReduceIndex.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/VfsAwareMapReduceIndex.java
@@ -72,7 +72,7 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
   protected VfsAwareMapReduceIndex(@NotNull IndexExtension<Key, Value, Input> extension,
                                    @NotNull IndexStorage<Key, Value> storage,
                                    @Nullable ForwardIndex forwardIndexMap,
-                                   @Nullable ForwardIndexAccessor<Key, Value, ?, Input> forwardIndexAccessor,
+                                   @Nullable ForwardIndexAccessor<Key, Value> forwardIndexAccessor,
                                    @Nullable SnapshotInputMappingIndex<Key, Value, Input> snapshotInputMappings) {
     super(extension, storage, forwardIndexMap, forwardIndexAccessor, null);
     SharedIndicesData.registerIndex((ID<Key, Value>)myIndexId, extension);
@@ -89,10 +89,10 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
 
   @NotNull
   @Override
-  protected Map<Key, Value> mapInput(@Nullable Input content) {
-    Map<Key, Value> data;
+  protected InputData<Key, Value> mapInput(@Nullable Input content) {
+    InputData<Key, Value> data;
     boolean containsSnapshotData = true;
-    if (mySnapshotInputMappings != null && !myInMemoryMode.get() && content != null) {
+    if (mySnapshotInputMappings != null && content != null) {
       try {
         data = mySnapshotInputMappings.readData(content);
         if (data != null) {
@@ -108,7 +108,7 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
     data = super.mapInput(content);
     if (!containsSnapshotData) {
       try {
-        ((UpdatableSnapshotInputMappingIndex)mySnapshotInputMappings).putData(content, data);
+        return ((UpdatableSnapshotInputMappingIndex)mySnapshotInputMappings).putData(content, data);
       }
       catch (IOException e) {
         throw new RuntimeException(e);
@@ -140,13 +140,13 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
   }
 
   @Override
-  protected void updateForwardIndex(int inputId, @NotNull Map<Key, Value> data, @Nullable Object forwardIndexData) throws IOException {
+  protected void updateForwardIndex(int inputId, @NotNull InputData<Key, Value> data) throws IOException {
     if (myInMemoryMode.get()) {
       synchronized (myInMemoryKeysAndValues) {
-        myInMemoryKeysAndValues.put(inputId, data);
+        myInMemoryKeysAndValues.put(inputId, data.getKeyValues());
       }
     } else {
-      super.updateForwardIndex(inputId, data, forwardIndexData);
+      super.updateForwardIndex(inputId, data);
     }
   }
 
@@ -248,7 +248,7 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
     }
     if (getForwardIndexAccessor() instanceof AbstractMapForwardIndexAccessor) {
       ByteArraySequence serializedInputData = getForwardIndexMap().get(fileId);
-      AbstractMapForwardIndexAccessor<Key, Value, ?, Input> forwardIndexAccessor = (AbstractMapForwardIndexAccessor<Key, Value, ?, Input>)getForwardIndexAccessor();
+      AbstractMapForwardIndexAccessor<Key, Value, ?> forwardIndexAccessor = (AbstractMapForwardIndexAccessor<Key, Value, ?>)getForwardIndexAccessor();
       return forwardIndexAccessor.convertToInputDataMap(serializedInputData);
     }
     // in future we will get rid of forward index for SingleEntryFileBasedIndexExtension
@@ -319,7 +319,7 @@ public class VfsAwareMapReduceIndex<Key, Value, Input> extends MapReduceIndex<Ke
   }
 
   @Nullable
-  private static <Key, Value, Input> ForwardIndexAccessor<Key, Value, ?, Input> getForwardIndexAccessor(@NotNull IndexExtension<Key, Value, Input> indexExtension) {
+  private static <Key, Value> ForwardIndexAccessor<Key, Value> getForwardIndexAccessor(@NotNull IndexExtension<Key, Value, ?> indexExtension) {
     if (!shouldCreateForwardIndex(indexExtension)) return null;
     return new MapForwardIndexAccessor<>(new InputMapExternalizer<>(indexExtension));
   }
diff --git a/platform/util/src/com/intellij/util/indexing/impl/InputData.java b/platform/util/src/com/intellij/util/indexing/impl/InputData.java
new file mode 100644
index 000000000000..1761f3a44217
--- /dev/null
+++ b/platform/util/src/com/intellij/util/indexing/impl/InputData.java
@@ -0,0 +1,28 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.util.indexing.impl;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.Map;
+
+public class InputData<Key, Value> {
+  private static final InputData EMPTY = new InputData<>(Collections.emptyMap());
+
+  @SuppressWarnings("unchecked")
+  public static <Key, Value> InputData<Key, Value> empty() {
+    return EMPTY;
+  }
+
+  @NotNull
+  private final Map<Key, Value> myKeyValues;
+
+  protected InputData(@NotNull Map<Key, Value> values) {
+    myKeyValues = values;
+  }
+
+  @NotNull
+  public Map<Key, Value> getKeyValues() {
+    return myKeyValues;
+  }
+}
diff --git a/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java b/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
index 1db858cf0985..4e3c0c544ade 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
@@ -56,7 +56,7 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
   protected final ForwardIndex<Key, Value> myForwardIndex;
   //new
   private final com.intellij.util.indexing.impl.forward.ForwardIndex myForwardIndexMap;
-  private final ForwardIndexAccessor<Key, Value, ?, Input> myForwardIndexAccessor;
+  private final ForwardIndexAccessor<Key, Value> myForwardIndexAccessor;
 
   private final ReentrantReadWriteLock myLock = createLock();
   private final boolean myUseIntForwardIndex;
@@ -85,7 +85,7 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
   protected MapReduceIndex(@NotNull IndexExtension<Key, Value, Input> extension,
                            @NotNull IndexStorage<Key, Value> storage,
                            @Nullable com.intellij.util.indexing.impl.forward.ForwardIndex forwardIndexMap,
-                           @Nullable ForwardIndexAccessor<Key, Value, ?, Input> forwardIndexAccessor,
+                           @Nullable ForwardIndexAccessor<Key, Value> forwardIndexAccessor,
                            @Nullable ForwardIndex<Key, Value> forwardIndex) {
     myIndexId = extension.getName();
     myExtension = extension;
@@ -102,7 +102,7 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
   protected MapReduceIndex(@NotNull IndexExtension<Key, Value, Input> extension,
                            @NotNull IndexStorage<Key, Value> storage,
                            @Nullable com.intellij.util.indexing.impl.forward.ForwardIndex forwardIndex,
-                           @Nullable ForwardIndexAccessor<Key, Value, ?, Input> forwardIndexAccessor) {
+                           @Nullable ForwardIndexAccessor<Key, Value> forwardIndexAccessor) {
     this(extension, storage, forwardIndex, forwardIndexAccessor, null);
   }
 
@@ -117,7 +117,7 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
     return myForwardIndexMap;
   }
 
-  public ForwardIndexAccessor<Key, Value, ?, Input> getForwardIndexAccessor() {
+  public ForwardIndexAccessor<Key, Value> getForwardIndexAccessor() {
     return myForwardIndexAccessor;
   }
 
@@ -266,26 +266,19 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
 
   @NotNull
   protected UpdateData<Key, Value> calculateUpdateData(final int inputId, @Nullable Input content) {
-    final Map<Key, Value> data = mapInput(content);
-    Object forwardIndexData;
-    if (myForwardIndexAccessor != null) {
-      forwardIndexData = myForwardIndexAccessor.convertToDataType(data, content);
-    } else {
-      forwardIndexData = null;
-    }
-    return createUpdateData(data,
+    final InputData<Key, Value> data = mapInput(content);
+    return createUpdateData(data.getKeyValues(),
                             () -> getKeysDiffBuilder(inputId),
-                            () -> updateForwardIndex(inputId, data, forwardIndexData));
+                            () -> updateForwardIndex(inputId, data));
   }
 
-  protected void updateForwardIndex(int inputId, @NotNull Map<Key, Value> data, @Nullable Object forwardIndexData) throws IOException {
-    if (myForwardIndex != null) myForwardIndex.putInputData(inputId, data);
+  protected void updateForwardIndex(int inputId, @NotNull InputData<Key, Value> data) throws IOException {
+    if (myForwardIndex != null) myForwardIndex.putInputData(inputId, data.getKeyValues());
     if (myForwardIndexMap != null) {
       if (myUseIntForwardIndex) {
-        ((IntForwardIndex)myForwardIndexMap).putInt(inputId, (Integer)forwardIndexData);
+        ((IntForwardIndex)myForwardIndexMap).putInt(inputId, ((IntForwardIndexAccessor<Key, Value>)myForwardIndexAccessor).serializeIndexedDataToInt(data));
       } else {
-        //noinspection unchecked
-        myForwardIndexMap.put(inputId, ((ForwardIndexAccessor)myForwardIndexAccessor).serializeIndexedData(forwardIndexData));
+        myForwardIndexMap.put(inputId, myForwardIndexAccessor.serializeIndexedData(data));
       }
     }
   }
@@ -313,14 +306,14 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
   }
 
   @NotNull
-  protected Map<Key, Value> mapInput(@Nullable Input content) {
+  protected InputData<Key, Value> mapInput(@Nullable Input content) {
     if (content == null) {
-      return Collections.emptyMap();
+      return InputData.empty();
     }
     Map<Key, Value> data = myIndexer.map(content);
     checkValuesHaveProperEqualsAndHashCode(data, myIndexId, myValueExternalizer);
     checkCanceled();
-    return data;
+    return new InputData<>(data);
   }
 
   public abstract void checkCanceled();
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractForwardIndexAccessor.java
index cb57a5b0c829..539b58e161a8 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractForwardIndexAccessor.java
@@ -5,6 +5,7 @@ import com.intellij.openapi.util.ThreadLocalCachedByteArray;
 import com.intellij.openapi.util.io.BufferExposingByteArrayOutputStream;
 import com.intellij.openapi.util.io.ByteArraySequence;
 import com.intellij.util.containers.ContainerUtil;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
 import com.intellij.util.io.DataExternalizer;
 import com.intellij.util.io.DataOutputStream;
@@ -18,7 +19,7 @@ import java.io.IOException;
 import java.util.Map;
 
 @ApiStatus.Experimental
-public abstract class AbstractForwardIndexAccessor<Key, Value, DataType, Input> implements ForwardIndexAccessor<Key, Value, DataType, Input> {
+public abstract class AbstractForwardIndexAccessor<Key, Value, DataType> implements ForwardIndexAccessor<Key, Value> {
   @NotNull
   private final DataExternalizer<DataType> myDataTypeExternalizer;
 
@@ -40,8 +41,16 @@ public abstract class AbstractForwardIndexAccessor<Key, Value, DataType, Input>
     return createDiffBuilder(inputId, deserializeData(sequence));
   }
 
+  @Nullable
+  public abstract DataType convertToDataType(@NotNull InputData<Key, Value> data);
+
   @Nullable
   @Override
+  public ByteArraySequence serializeIndexedData(@NotNull InputData<Key, Value> data) throws IOException {
+    return serializeIndexedData(convertToDataType(data));
+  }
+
+  @Nullable
   public ByteArraySequence serializeIndexedData(@Nullable DataType data) throws IOException {
     if (data == null) return null;
     return serializeToByteSeq(data, myDataTypeExternalizer, getBufferInitialSize(data));
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractMapForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractMapForwardIndexAccessor.java
index 8e67ffafdfc0..c09e785d53d0 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractMapForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/AbstractMapForwardIndexAccessor.java
@@ -11,7 +11,7 @@ import org.jetbrains.annotations.Nullable;
 import java.io.IOException;
 import java.util.Map;
 
-public abstract class AbstractMapForwardIndexAccessor<Key, Value, DataType, Input> extends AbstractForwardIndexAccessor<Key, Value, DataType, Input> {
+public abstract class AbstractMapForwardIndexAccessor<Key, Value, DataType> extends AbstractForwardIndexAccessor<Key, Value, DataType> {
   public AbstractMapForwardIndexAccessor(@NotNull DataExternalizer<DataType> externalizer) {
     super(externalizer);
   }
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/ForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/ForwardIndexAccessor.java
index cd1368cd51dc..e4b97517f88a 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/ForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/ForwardIndexAccessor.java
@@ -2,32 +2,26 @@
 package com.intellij.util.indexing.impl.forward;
 
 import com.intellij.openapi.util.io.ByteArraySequence;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.io.IOException;
 import java.util.Map;
 
-/**
- *
- * @param <DataType> should not hold strong reference to Input because it may lead to OOMs
- */
-public interface ForwardIndexAccessor<Key, Value, DataType, Input> {
+@ApiStatus.Experimental
+public interface ForwardIndexAccessor<Key, Value> {
   /**
    * creates a diff builder for given inputId.
    */
   @NotNull
   InputDataDiffBuilder<Key, Value> getDiffBuilder(int inputId, @Nullable ByteArraySequence sequence) throws IOException;
 
-  /**
-   * convert mapped key-values and input to a data type before it will be serialized
-   */
-  DataType convertToDataType(@Nullable Map<Key, Value> map, @Nullable Input content);
-
   /**
    * serialize indexed data to forward index format.
    */
   @Nullable
-  ByteArraySequence serializeIndexedData(@Nullable DataType data) throws IOException;
+  ByteArraySequence serializeIndexedData(@NotNull InputData<Key, Value> data) throws IOException;
 }
\ No newline at end of file
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/IntForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/IntForwardIndexAccessor.java
index 26501c30133a..e0404ae75ced 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/IntForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/IntForwardIndexAccessor.java
@@ -2,6 +2,7 @@
 package com.intellij.util.indexing.impl.forward;
 
 import com.intellij.openapi.util.io.ByteArraySequence;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
 import com.intellij.util.io.EnumeratorIntegerDescriptor;
 import org.jetbrains.annotations.NotNull;
@@ -10,22 +11,17 @@ import org.jetbrains.annotations.Nullable;
 import java.io.IOException;
 import java.util.Map;
 
-public interface IntForwardIndexAccessor<Key, Value, Input> extends ForwardIndexAccessor<Key, Value, Integer, Input> {
+public interface IntForwardIndexAccessor<Key, Value> extends ForwardIndexAccessor<Key, Value> {
   @NotNull
   @Override
   default InputDataDiffBuilder<Key, Value> getDiffBuilder(int inputId, @Nullable ByteArraySequence sequence) throws IOException {
     return getDiffBuilderFromInt(inputId, sequence == null ? 0 : AbstractForwardIndexAccessor.deserializeFromByteSeq(sequence, EnumeratorIntegerDescriptor.INSTANCE));
   }
 
-  @Override
-  default Integer convertToDataType(@Nullable Map<Key, Value> map, @Nullable Input content) {
-    return convertToInt(map, content);
-  }
-
   @Nullable
   @Override
-  default ByteArraySequence serializeIndexedData(@Nullable Integer data) throws IOException {
-    return data == null ? null : AbstractForwardIndexAccessor.serializeToByteSeq(data, EnumeratorIntegerDescriptor.INSTANCE, 8);
+  default ByteArraySequence serializeIndexedData(@NotNull InputData<Key, Value> data) throws IOException {
+    return AbstractForwardIndexAccessor.serializeToByteSeq(serializeIndexedDataToInt(data), EnumeratorIntegerDescriptor.INSTANCE, 8);
   }
 
   /**
@@ -34,8 +30,5 @@ public interface IntForwardIndexAccessor<Key, Value, Input> extends ForwardIndex
   @NotNull
   InputDataDiffBuilder<Key, Value> getDiffBuilderFromInt(int inputId, int value) throws IOException;
 
-  /**
-   * convert mapped key-values and input to a data type before it will be serialized
-   */
-  int convertToInt(@Nullable Map<Key, Value> map, @Nullable Input content);
+  int serializeIndexedDataToInt(@NotNull InputData<Key, Value> data);
 }
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/KeyCollectionForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/KeyCollectionForwardIndexAccessor.java
index ad3d2b862ede..e66324e782c4 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/KeyCollectionForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/KeyCollectionForwardIndexAccessor.java
@@ -5,6 +5,7 @@ import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.indexing.IndexExtension;
 import com.intellij.util.indexing.IndexId;
 import com.intellij.util.indexing.impl.CollectionInputDataDiffBuilder;
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.indexing.impl.InputDataDiffBuilder;
 import com.intellij.util.indexing.impl.InputIndexDataExternalizer;
 import com.intellij.util.io.DataExternalizer;
@@ -13,16 +14,18 @@ import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.io.IOException;
 import java.util.Collection;
 import java.util.Map;
+import java.util.Set;
 
 @ApiStatus.Experimental
-public class KeyCollectionForwardIndexAccessor<Key, Value, Input> extends AbstractForwardIndexAccessor<Key, Value, Collection<Key>, Input> {
+public class KeyCollectionForwardIndexAccessor<Key, Value> extends AbstractForwardIndexAccessor<Key, Value, Collection<Key>> {
   public KeyCollectionForwardIndexAccessor(@NotNull DataExternalizer<Collection<Key>> externalizer) {
     super(externalizer);
   }
 
-  public KeyCollectionForwardIndexAccessor(@NotNull IndexExtension<Key, Value, Input> extension) {
+  public KeyCollectionForwardIndexAccessor(@NotNull IndexExtension<Key, Value, ?> extension) {
     this(extension.getKeyDescriptor(), extension.getName());
   }
 
@@ -35,9 +38,11 @@ public class KeyCollectionForwardIndexAccessor<Key, Value, Input> extends Abstra
     return new CollectionInputDataDiffBuilder<>(inputId, keys);
   }
 
+  @Nullable
   @Override
-  public Collection<Key> convertToDataType(@Nullable Map<Key, Value> map, @Nullable Input content) {
-    return ContainerUtil.isEmpty(map) ? null : map.keySet();
+  public Collection<Key> convertToDataType(@NotNull InputData<Key, Value> data) {
+    Set<Key> keys = data.getKeyValues().keySet();
+    return keys.isEmpty() ? null : keys;
   }
 
   @Override
diff --git a/platform/util/src/com/intellij/util/indexing/impl/forward/MapForwardIndexAccessor.java b/platform/util/src/com/intellij/util/indexing/impl/forward/MapForwardIndexAccessor.java
index fb907c0d3bc2..b15cc162d024 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/forward/MapForwardIndexAccessor.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/forward/MapForwardIndexAccessor.java
@@ -1,13 +1,15 @@
 // Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.util.indexing.impl.forward;
 
+import com.intellij.util.indexing.impl.InputData;
 import com.intellij.util.io.DataExternalizer;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.io.IOException;
 import java.util.Map;
 
-public class MapForwardIndexAccessor<Key, Value, Input> extends AbstractMapForwardIndexAccessor<Key, Value, Map<Key, Value>, Input> {
+public class MapForwardIndexAccessor<Key, Value, Input> extends AbstractMapForwardIndexAccessor<Key, Value, Map<Key, Value>> {
   public MapForwardIndexAccessor(@NotNull DataExternalizer<Map<Key, Value>> externalizer) {
     super(externalizer);
   }
@@ -22,9 +24,9 @@ public class MapForwardIndexAccessor<Key, Value, Input> extends AbstractMapForwa
   protected int getBufferInitialSize(@NotNull Map<Key, Value> map) {
     return 4 * map.size();
   }
-
+  @Nullable
   @Override
-  public Map<Key, Value> convertToDataType(@Nullable Map<Key, Value> map, @Nullable Input content) {
-    return map;
+  public Map<Key, Value> convertToDataType(@NotNull InputData<Key, Value> data) {
+    return data.getKeyValues();
   }
 }