merging_iterator.h

//  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 {

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