/src/leveldb/table/merger.cc

Source (jump to first uncovered line)
// 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.

#include "table/merger.h"

#include "leveldb/comparator.h"
#include "leveldb/iterator.h"
#include "table/iterator_wrapper.h"

namespace leveldb {

namespace {
class MergingIterator : public Iterator {
 public:
  MergingIterator(const Comparator* comparator, Iterator** children, int n)
      : comparator_(comparator),
        children_(new IteratorWrapper[n]),
        n_(n),
        current_(nullptr),
        direction_(kForward) {
    for (int i = 0; i < n; i++) {
      children_[i].Set(children[i]);
    }
  }

  ~MergingIterator() override { delete[] children_; }

  bool Valid() const override { return (current_ != nullptr); }

  void SeekToFirst() override {
    for (int i = 0; i < n_; i++) {
      children_[i].SeekToFirst();
    }
    FindSmallest();
    direction_ = kForward;
  }

  void SeekToLast() override {
    for (int i = 0; i < n_; i++) {
      children_[i].SeekToLast();
    }
    FindLargest();
    direction_ = kReverse;
  }

  void Seek(const Slice& target) override {
    for (int i = 0; i < n_; i++) {
      children_[i].Seek(target);
    }
    FindSmallest();
    direction_ = kForward;
  }

  void Next() override {
    assert(Valid());

    // Ensure that all children are positioned after key().
    // If we are moving in the forward direction, it is already
    // true for all of the non-current_ children since current_ is
    // the smallest child and key() == current_->key().  Otherwise,
    // we explicitly position the non-current_ children.
    if (direction_ != kForward) {
      for (int i = 0; i < n_; i++) {
        IteratorWrapper* child = &children_[i];
        if (child != current_) {
          child->Seek(key());
          if (child->Valid() &&
              comparator_->Compare(key(), child->key()) == 0) {
            child->Next();
          }
        }
      }
      direction_ = kForward;
    }

    current_->Next();
    FindSmallest();
  }

  void Prev() override {
    assert(Valid());

    // Ensure that all children are positioned before key().
    // If we are moving in the reverse direction, it is already
    // true for all of the non-current_ children since current_ is
    // the largest child and key() == current_->key().  Otherwise,
    // we explicitly position the non-current_ children.
    if (direction_ != kReverse) {
      for (int i = 0; i < n_; i++) {
        IteratorWrapper* child = &children_[i];
        if (child != current_) {
          child->Seek(key());
          if (child->Valid()) {
            // Child is at first entry >= key().  Step back one to be < key()
            child->Prev();
          } else {
            // Child has no entries >= key().  Position at last entry.
            child->SeekToLast();
          }
        }
      }
      direction_ = kReverse;
    }

    current_->Prev();
    FindLargest();
  }

  Slice key() const override {
    assert(Valid());
    return current_->key();
  }

  Slice value() const override {
    assert(Valid());
    return current_->value();
  }

  Status status() const override {
    Status status;
    for (int i = 0; i < n_; i++) {
      status = children_[i].status();
      if (!status.ok()) {
        break;
      }
    }
    return status;
  }

 private:
  // Which direction is the iterator moving?
  enum Direction { kForward, kReverse };

  void FindSmallest();
  void FindLargest();

  // We might want to use a heap in case there are lots of children.
  // For now we use a simple array since we expect a very small number
  // of children in leveldb.
  const Comparator* comparator_;
  IteratorWrapper* children_;
  int n_;
  IteratorWrapper* current_;
  Direction direction_;
};

void MergingIterator::FindSmallest() {
  IteratorWrapper* smallest = nullptr;
  for (int i = 0; i < n_; i++) {
    IteratorWrapper* child = &children_[i];
    if (child->Valid()) {
      if (smallest == nullptr) {
        smallest = child;
      } else if (comparator_->Compare(child->key(), smallest->key()) < 0) {
        smallest = child;
      }
    }
  }
  current_ = smallest;
}

void MergingIterator::FindLargest() {
  IteratorWrapper* largest = nullptr;
  for (int i = n_ - 1; i >= 0; i--) {
    IteratorWrapper* child = &children_[i];
    if (child->Valid()) {
      if (largest == nullptr) {
        largest = child;
      } else if (comparator_->Compare(child->key(), largest->key()) > 0) {
        largest = child;
      }
    }
  }
  current_ = largest;
}
}  // namespace

Iterator* NewMergingIterator(const Comparator* comparator, Iterator** children,
                             int n) {
  assert(n >= 0);
  if (n == 0) {
    return NewEmptyIterator();
  } else if (n == 1) {
    return children[0];
  } else {
    return new MergingIterator(comparator, children, n);
  }
}

}  // namespace leveldb

Line	Count	Source (jump to first uncovered line)
1		// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2		// Use of this source code is governed by a BSD-style license that can be
3		// found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5		#include "table/merger.h"
6
7		#include "leveldb/comparator.h"
8		#include "leveldb/iterator.h"
9		#include "table/iterator_wrapper.h"
10
11		namespace leveldb {
12
13		namespace {
14		class MergingIterator : public Iterator {
15		public:
16		MergingIterator(const Comparator* comparator, Iterator** children, int n)
17	149k	: comparator_(comparator),
18	149k	children_(new IteratorWrapper[n]),
19	149k	n_(n),
20	149k	current_(nullptr),
21	149k	direction_(kForward) {
22	805k	for (int i = 0; i < n; i++) {
23	656k	children_[i].Set(children[i]);
24	656k	}
25	149k	}
26
27	149k	~MergingIterator() override { delete[] children_; }
28
29	6.91M	bool Valid() const override { return (current_ != nullptr); }
30
31	78.2k	void SeekToFirst() override {
32	410k	for (int i = 0; i < n_; i++) {
33	332k	children_[i].SeekToFirst();
34	332k	}
35	78.2k	FindSmallest();
36	78.2k	direction_ = kForward;
37	78.2k	}
38
39	0	void SeekToLast() override {
40	0	for (int i = 0; i < n_; i++) {
41	0	children_[i].SeekToLast();
42	0	}
43	0	FindLargest();
44	0	direction_ = kReverse;
45	0	}
46
47	0	void Seek(const Slice& target) override {
48	0	for (int i = 0; i < n_; i++) {
49	0	children_[i].Seek(target);
50	0	}
51	0	FindSmallest();
52	0	direction_ = kForward;
53	0	}
54
55	6.83M	void Next() override {
56	6.83M	assert(Valid());
57
58		// Ensure that all children are positioned after key().
59		// If we are moving in the forward direction, it is already
60		// true for all of the non-current_ children since current_ is
61		// the smallest child and key() == current_->key(). Otherwise,
62		// we explicitly position the non-current_ children.
63	6.83M	if (direction_ != kForward) {
64	0	for (int i = 0; i < n_; i++) {
65	0	IteratorWrapper* child = &children_[i];
66	0	if (child != current_) {
67	0	child->Seek(key());
68	0	if (child->Valid() &&
69	0	comparator_->Compare(key(), child->key()) == 0) {
70	0	child->Next();
71	0	}
72	0	}
73	0	}
74	0	direction_ = kForward;
75	0	}
76
77	6.83M	current_->Next();
78	6.83M	FindSmallest();
79	6.83M	}
80
81	0	void Prev() override {
82	0	assert(Valid());
83
84		// Ensure that all children are positioned before key().
85		// If we are moving in the reverse direction, it is already
86		// true for all of the non-current_ children since current_ is
87		// the largest child and key() == current_->key(). Otherwise,
88		// we explicitly position the non-current_ children.
89	0	if (direction_ != kReverse) {
90	0	for (int i = 0; i < n_; i++) {
91	0	IteratorWrapper* child = &children_[i];
92	0	if (child != current_) {
93	0	child->Seek(key());
94	0	if (child->Valid()) {
95		// Child is at first entry >= key(). Step back one to be < key()
96	0	child->Prev();
97	0	} else {
98		// Child has no entries >= key(). Position at last entry.
99	0	child->SeekToLast();
100	0	}
101	0	}
102	0	}
103	0	direction_ = kReverse;
104	0	}
105
106	0	current_->Prev();
107	0	FindLargest();
108	0	}
109
110	7.15M	Slice key() const override {
111	7.15M	assert(Valid());
112	7.15M	return current_->key();
113	7.15M	}
114
115	5.90M	Slice value() const override {
116	5.90M	assert(Valid());
117	5.90M	return current_->value();
118	5.90M	}
119
120	29.2k	Status status() const override {
121	29.2k	Status status;
122	118k	for (int i = 0; i < n_; i++) {
123	89.6k	status = children_[i].status();
124	89.6k	if (!status.ok()) {
125	0	break;
126	0	}
127	89.6k	}
128	29.2k	return status;
129	29.2k	}
130
131		private:
132		// Which direction is the iterator moving?
133		enum Direction { kForward, kReverse };
134
135		void FindSmallest();
136		void FindLargest();
137
138		// We might want to use a heap in case there are lots of children.
139		// For now we use a simple array since we expect a very small number
140		// of children in leveldb.
141		const Comparator* comparator_;
142		IteratorWrapper* children_;
143		int n_;
144		IteratorWrapper* current_;
145		Direction direction_;
146		};
147
148	6.93M	void MergingIterator::FindSmallest() {
149	6.93M	IteratorWrapper* smallest = nullptr;
150	30.7M	for (int i = 0; i < n_; i++) {
151	23.8M	IteratorWrapper* child = &children_[i];
152	23.8M	if (child->Valid()) {
153	15.4M	if (smallest == nullptr) {
154	6.85M	smallest = child;
155	8.61M	} else if (comparator_->Compare(child->key(), smallest->key()) < 0) {
156	3.37M	smallest = child;
157	3.37M	}
158	15.4M	}
159	23.8M	}
160	6.93M	current_ = smallest;
161	6.93M	}
162
163	0	void MergingIterator::FindLargest() {
164	0	IteratorWrapper* largest = nullptr;
165	0	for (int i = n_ - 1; i >= 0; i--) {
166	0	IteratorWrapper* child = &children_[i];
167	0	if (child->Valid()) {
168	0	if (largest == nullptr) {
169	0	largest = child;
170	0	} else if (comparator_->Compare(child->key(), largest->key()) > 0) {
171	0	largest = child;
172	0	}
173	0	}
174	0	}
175	0	current_ = largest;
176	0	}
177		} // namespace
178
179		Iterator* NewMergingIterator(const Comparator* comparator, Iterator** children,
180	170k	int n) {
181	170k	assert(n >= 0);
182	170k	if (n == 0) {
183	0	return NewEmptyIterator();
184	170k	} else if (n == 1) {
185	21.3k	return children[0];
186	149k	} else {
187	149k	return new MergingIterator(comparator, children, n);
188	149k	}
189	170k	}
190
191		} // namespace leveldb

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Created: 2025-07-11 07:01