diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeKindCacheImpl.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeKindCacheImpl.java
index f3d1455..389d53a 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeKindCacheImpl.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeKindCacheImpl.java
@@ -27,6 +27,7 @@
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.git.InMemoryInserter;
 import com.google.gerrit.server.git.MergeUtil;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
@@ -39,6 +40,7 @@
 import org.eclipse.jgit.errors.LargeObjectException;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.merge.ThreeWayMerger;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -217,10 +219,10 @@
         // A trivial rebase can be detected by looking for the next commit
         // having the same tree as would exist when the prior commit is
         // cherry-picked onto the next commit's new first parent.
-        ThreeWayMerger merger = MergeUtil.newThreeWayMerger(
-            repo, MergeUtil.createDryRunInserter(repo), key.strategyName);
-        merger.setBase(prior.getParent(0));
-        try {
+        try (ObjectInserter ins = new InMemoryInserter(repo)) {
+          ThreeWayMerger merger =
+              MergeUtil.newThreeWayMerger(repo, ins, key.strategyName);
+          merger.setBase(prior.getParent(0));
           if (merger.merge(next.getParent(0), prior)
               && merger.getResultTreeId().equals(next.getTree())) {
             return ChangeKind.TRIVIAL_REBASE;
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/InMemoryInserter.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/InMemoryInserter.java
new file mode 100644
index 0000000..4c7f637
--- /dev/null
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/InMemoryInserter.java
@@ -0,0 +1,142 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.git;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.collect.ImmutableList;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Set;
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
+import org.eclipse.jgit.lib.AbbreviatedObjectId;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.transport.PackParser;
+
+public class InMemoryInserter extends ObjectInserter {
+  private final ObjectReader reader;
+  private final Map<ObjectId, InsertedObject> inserted = new LinkedHashMap<>();
+  private final boolean closeReader;
+
+  public InMemoryInserter(ObjectReader reader) {
+    this.reader = checkNotNull(reader);
+    closeReader = false;
+  }
+
+  public InMemoryInserter(Repository repo) {
+    this.reader = repo.newObjectReader();
+    closeReader = true;
+  }
+
+  @Override
+  public ObjectId insert(int type, long length, InputStream in) throws IOException {
+    return insert(InsertedObject.create(type, in));
+  }
+
+  @Override
+  public ObjectId insert(int type, byte[] data) {
+    return insert(type, data, 0, data.length);
+  }
+
+  @Override
+  public ObjectId insert(int type, byte[] data, int off, int len) {
+    return insert(InsertedObject.create(type, data, off, len));
+  }
+
+  public ObjectId insert(InsertedObject obj) {
+    inserted.put(obj.id(), obj);
+    return obj.id();
+  }
+
+  @Override
+  public PackParser newPackParser(InputStream in) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public ObjectReader newReader() {
+    return new Reader();
+  }
+
+  @Override
+  public void flush() {
+    // Do nothing; objects are not written to the repo.
+  }
+
+  @Override
+  public void close() {
+    if (closeReader) {
+      reader.close();
+    }
+  }
+
+  public ImmutableList<InsertedObject> getInsertedObjects() {
+    return ImmutableList.copyOf(inserted.values());
+  }
+
+  public void clear() {
+    inserted.clear();
+  }
+
+  private class Reader extends ObjectReader {
+    @Override
+    public ObjectReader newReader() {
+      return new Reader();
+    }
+
+    @Override
+    public Collection<ObjectId> resolve(AbbreviatedObjectId id) throws IOException {
+      Set<ObjectId> result = new HashSet<>();
+      for (ObjectId insId : inserted.keySet()) {
+        if (id.prefixCompare(insId) == 0) {
+          result.add(insId);
+        }
+      }
+      result.addAll(reader.resolve(id));
+      return result;
+    }
+
+    @Override
+    public ObjectLoader open(AnyObjectId objectId, int typeHint) throws IOException {
+      InsertedObject obj = inserted.get(objectId);
+      if (obj == null) {
+        return reader.open(objectId, typeHint);
+      }
+      if (typeHint != OBJ_ANY && obj.type() != typeHint) {
+        throw new IncorrectObjectTypeException(objectId.copy(), typeHint);
+      }
+      return obj.newLoader();
+    }
+
+    @Override
+    public Set<ObjectId> getShallowCommits() throws IOException {
+      return reader.getShallowCommits();
+    }
+
+    @Override
+    public void close() {
+      // Do nothing; this class owns no open resources.
+    }
+  }
+}
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/InsertedObject.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/InsertedObject.java
new file mode 100644
index 0000000..8a766af
--- /dev/null
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/InsertedObject.java
@@ -0,0 +1,54 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.git;
+
+import com.google.auto.value.AutoValue;
+import com.google.protobuf.ByteString;
+import java.io.IOException;
+import java.io.InputStream;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.ObjectLoader;
+
+@AutoValue
+public abstract class InsertedObject {
+  static InsertedObject create(int type, InputStream in) throws IOException {
+    return create(type, ByteString.readFrom(in));
+  }
+
+  static InsertedObject create(int type, ByteString bs) {
+    ObjectId id;
+    try (ObjectInserter.Formatter fmt = new ObjectInserter.Formatter()) {
+      id = fmt.idFor(type, bs.size(), bs.newInput());
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+    return new AutoValue_InsertedObject(id, type, bs);
+  }
+
+  static InsertedObject create(int type, byte[] src, int off, int len) {
+    return create(type, ByteString.copyFrom(src, off, len));
+  }
+
+  public abstract ObjectId id();
+
+  public abstract int type();
+
+  public abstract ByteString data();
+
+  ObjectLoader newLoader() {
+    return new ObjectLoader.SmallObject(type(), data().toByteArray());
+  }
+}
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/MergeUtil.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/MergeUtil.java
index 2025e99..13476ef 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/git/MergeUtil.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/MergeUtil.java
@@ -66,13 +66,12 @@
 import org.eclipse.jgit.revwalk.RevFlag;
 import org.eclipse.jgit.revwalk.RevSort;
 import org.eclipse.jgit.revwalk.RevWalk;
-import org.eclipse.jgit.transport.PackParser;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
-import java.io.InputStream;
 import java.io.UnsupportedEncodingException;
+
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -353,9 +352,9 @@
       return false;
     }
 
-    ThreeWayMerger m = newThreeWayMerger(repo, createDryRunInserter(repo));
-    try {
-      return m.merge(new AnyObjectId[] {mergeTip, toMerge});
+    try (ObjectInserter ins = new InMemoryInserter(repo)) {
+      return newThreeWayMerger(repo, ins)
+          .merge(new AnyObjectId[] {mergeTip, toMerge});
     } catch (LargeObjectException e) {
       log.warn("Cannot merge due to LargeObjectException: " + toMerge.name());
       return false;
@@ -401,8 +400,8 @@
       // taking the delta relative to that one parent and redoing
       // that on the current merge tip.
       //
-      try {
-        ThreeWayMerger m = newThreeWayMerger(repo, createDryRunInserter(repo));
+      try (ObjectInserter ins = new InMemoryInserter(repo)) {
+        ThreeWayMerger m = newThreeWayMerger(repo, ins);
         m.setBase(toMerge.getParent(0));
         return m.merge(mergeTip, toMerge);
       } catch (IOException e) {
@@ -429,26 +428,6 @@
     }
   }
 
-  public static ObjectInserter createDryRunInserter(Repository db) {
-    final ObjectInserter delegate = db.newObjectInserter();
-    return new ObjectInserter.Filter() {
-      @Override
-      protected ObjectInserter delegate() {
-        return delegate;
-      }
-
-      @Override
-      public PackParser newPackParser(InputStream in) throws IOException {
-        throw new UnsupportedOperationException();
-      }
-
-      @Override
-      public void flush() throws IOException {
-        // Do nothing.
-      }
-    };
-  }
-
   public CodeReviewCommit mergeOneCommit(PersonIdent author,
       PersonIdent committer, Repository repo, CodeReviewRevWalk rw,
       ObjectInserter inserter, RevFlag canMergeFlag, Branch.NameKey destBranch,