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diff --git a/src/rocksdb/table/merging_iterator.h b/src/rocksdb/table/merging_iterator.h
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+++ b/src/rocksdb/table/merging_iterator.h
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+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#pragma once
+
+#include "db/dbformat.h"
+#include "rocksdb/types.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class Comparator;
+class Env;
+class Arena;
+template <class TValue>
+class InternalIteratorBase;
+using InternalIterator = InternalIteratorBase<Slice>;
+
+// Return an iterator that provided the union of the data in
+// children[0,n-1].  Takes ownership of the child iterators and
+// will delete them when the result iterator is deleted.
+//
+// The result does no duplicate suppression.  I.e., if a particular
+// key is present in K child iterators, it will be yielded K times.
+//
+// REQUIRES: n >= 0
+extern InternalIterator* NewMergingIterator(
+    const InternalKeyComparator* comparator, InternalIterator** children, int n,
+    Arena* arena = nullptr, bool prefix_seek_mode = false);
+
+class MergingIterator;
+
+// A builder class to build a merging iterator by adding iterators one by one.
+class MergeIteratorBuilder {
+ public:
+  // comparator: the comparator used in merging comparator
+  // arena: where the merging iterator needs to be allocated from.
+  explicit MergeIteratorBuilder(const InternalKeyComparator* comparator,
+                                Arena* arena, bool prefix_seek_mode = false);
+  ~MergeIteratorBuilder();
+
+  // Add iter to the merging iterator.
+  void AddIterator(InternalIterator* iter);
+
+  // Get arena used to build the merging iterator. It is called one a child
+  // iterator needs to be allocated.
+  Arena* GetArena() { return arena; }
+
+  // Return the result merging iterator.
+  InternalIterator* Finish();
+
+ private:
+  MergingIterator* merge_iter;
+  InternalIterator* first_iter;
+  bool use_merging_iter;
+  Arena* arena;
+};
+
+}  // namespace ROCKSDB_NAMESPACE