//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under the BSD-style license found in the
//  LICENSE file in the root directory of this source tree. An additional grant
//  of patent rights can be found in the PATENTS file in the same directory.

#include <string>
#include <vector>
#include <algorithm>
#include <utility>

#include "db/db_iter.h"
#include "db/dbformat.h"
#include "rocksdb/comparator.h"
#include "rocksdb/options.h"
#include "rocksdb/perf_context.h"
#include "rocksdb/slice.h"
#include "rocksdb/statistics.h"
#include "table/iterator_wrapper.h"
#include "table/merger.h"
#include "util/string_util.h"
#include "util/sync_point.h"
#include "util/testharness.h"
#include "utilities/merge_operators.h"

namespace rocksdb {

static uint64_t TestGetTickerCount(const Options& options,
                                   Tickers ticker_type) {
  return options.statistics->getTickerCount(ticker_type);
}

class TestIterator : public InternalIterator {
 public:
  explicit TestIterator(const Comparator* comparator)
      : initialized_(false),
        valid_(false),
        sequence_number_(0),
        iter_(0),
        cmp(comparator) {}

  void AddPut(std::string argkey, std::string argvalue) {
    Add(argkey, kTypeValue, argvalue);
  }

  void AddDeletion(std::string argkey) {
    Add(argkey, kTypeDeletion, std::string());
  }

  void AddSingleDeletion(std::string argkey) {
    Add(argkey, kTypeSingleDeletion, std::string());
  }

  void AddMerge(std::string argkey, std::string argvalue) {
    Add(argkey, kTypeMerge, argvalue);
  }

  void Add(std::string argkey, ValueType type, std::string argvalue) {
    Add(argkey, type, argvalue, sequence_number_++);
  }

  void Add(std::string argkey, ValueType type, std::string argvalue,
           size_t seq_num, bool update_iter = false) {
    valid_ = true;
    ParsedInternalKey internal_key(argkey, seq_num, type);
    data_.push_back(
        std::pair<std::string, std::string>(std::string(), argvalue));
    AppendInternalKey(&data_.back().first, internal_key);
    if (update_iter && valid_ && cmp.Compare(data_.back().first, key()) < 0) {
      // insert a key smaller than current key
      Finish();
      // data_[iter_] is not anymore the current element of the iterator.
      // Increment it to reposition it to the right position.
      iter_++;
    }
  }

  // should be called before operations with iterator
  void Finish() {
    initialized_ = true;
    std::sort(data_.begin(), data_.end(),
              [this](std::pair<std::string, std::string> a,
                     std::pair<std::string, std::string> b) {
      return (cmp.Compare(a.first, b.first) < 0);
    });
  }

  virtual bool Valid() const override {
    assert(initialized_);
    return valid_;
  }

  virtual void SeekToFirst() override {
    assert(initialized_);
    valid_ = (data_.size() > 0);
    iter_ = 0;
  }

  virtual void SeekToLast() override {
    assert(initialized_);
    valid_ = (data_.size() > 0);
    iter_ = data_.size() - 1;
  }

  virtual void Seek(const Slice& target) override {
    assert(initialized_);
    SeekToFirst();
    if (!valid_) {
      return;
    }
    while (iter_ < data_.size() &&
           (cmp.Compare(data_[iter_].first, target) < 0)) {
      ++iter_;
    }

    if (iter_ == data_.size()) {
      valid_ = false;
    }
  }

  virtual void SeekForPrev(const Slice& target) override {
    assert(initialized_);
    SeekForPrevImpl(target, &cmp);
  }

  virtual void Next() override {
    assert(initialized_);
    if (data_.empty() || (iter_ == data_.size() - 1)) {
      valid_ = false;
    } else {
      ++iter_;
    }
  }

  virtual void Prev() override {
    assert(initialized_);
    if (iter_ == 0) {
      valid_ = false;
    } else {
      --iter_;
    }
  }

  virtual Slice key() const override {
    assert(initialized_);
    return data_[iter_].first;
  }

  virtual Slice value() const override {
    assert(initialized_);
    return data_[iter_].second;
  }

  virtual Status status() const override {
    assert(initialized_);
    return Status::OK();
  }

  virtual bool IsKeyPinned() const override { return true; }
  virtual bool IsValuePinned() const override { return true; }

 private:
  bool initialized_;
  bool valid_;
  size_t sequence_number_;
  size_t iter_;

  InternalKeyComparator cmp;
  std::vector<std::pair<std::string, std::string>> data_;
};

class DBIteratorTest : public testing::Test {
 public:
  Env* env_;

  DBIteratorTest() : env_(Env::Default()) {}
};

TEST_F(DBIteratorTest, DBIteratorPrevNext) {
  Options options;

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddPut("a", "val_a");

    internal_iter->AddPut("b", "val_b");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");

    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "val_a");

    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());
  }
  // Test to check the SeekToLast() with iterate_upper_bound not set
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
  }

  // Test to check the SeekToLast() with iterate_upper_bound set
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("d", "val_d");
    internal_iter->AddPut("e", "val_e");
    internal_iter->AddPut("f", "val_f");
    internal_iter->Finish();

    Slice prefix("d");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
  }
  // Test to check the SeekToLast() iterate_upper_bound set to a key that
  // is not Put yet
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("d", "val_d");
    internal_iter->Finish();

    Slice prefix("z");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");

    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
  }
  // Test to check the SeekToLast() with iterate_upper_bound set to the
  // first key
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("b", "val_b");
    internal_iter->Finish();

    Slice prefix("a");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(!db_iter->Valid());
  }
  // Test case to check SeekToLast with iterate_upper_bound set
  // (same key put may times - SeekToLast should start with the
  // maximum sequence id of the upper bound)

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->AddPut("c", "val_c");
    internal_iter->Finish();

    Slice prefix("c");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        7, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    SetPerfLevel(kEnableCount);
    ASSERT_TRUE(GetPerfLevel() == kEnableCount);

    perf_context.Reset();
    db_iter->SeekToLast();

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(static_cast<int>(perf_context.internal_key_skipped_count), 7);
    ASSERT_EQ(db_iter->key().ToString(), "b");

    SetPerfLevel(kDisable);
  }
  // Test to check the SeekToLast() with the iterate_upper_bound set
  // (Checking the value of the key which has sequence ids greater than
  // and less that the iterator's sequence id)
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());

    internal_iter->AddPut("a", "val_a1");
    internal_iter->AddPut("a", "val_a2");
    internal_iter->AddPut("b", "val_b1");
    internal_iter->AddPut("c", "val_c1");
    internal_iter->AddPut("c", "val_c2");
    internal_iter->AddPut("c", "val_c3");
    internal_iter->AddPut("b", "val_b2");
    internal_iter->AddPut("d", "val_d1");
    internal_iter->Finish();

    Slice prefix("c");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        4, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b1");
  }

  // Test to check the SeekToLast() with the iterate_upper_bound set to the
  // key that is deleted
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddDeletion("a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->Finish();

    Slice prefix("a");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(!db_iter->Valid());
  }
  // Test to check the SeekToLast() with the iterate_upper_bound set
  // (Deletion cases)
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddDeletion("b");
    internal_iter->AddPut("c", "val_c");
    internal_iter->Finish();

    Slice prefix("c");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
  }
  // Test to check the SeekToLast() with iterate_upper_bound set
  // (Deletion cases - Lot of internal keys after the upper_bound
  // is deleted)
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->AddDeletion("c");
    internal_iter->AddDeletion("d");
    internal_iter->AddDeletion("e");
    internal_iter->AddDeletion("f");
    internal_iter->AddDeletion("g");
    internal_iter->AddDeletion("h");
    internal_iter->Finish();

    Slice prefix("c");

    ReadOptions ro;
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        7, options.max_sequential_skip_in_iterations, 0,
        ro.iterate_upper_bound));

    SetPerfLevel(kEnableCount);
    ASSERT_TRUE(GetPerfLevel() == kEnableCount);

    perf_context.Reset();
    db_iter->SeekToLast();

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(static_cast<int>(perf_context.internal_delete_skipped_count), 1);
    ASSERT_EQ(db_iter->key().ToString(), "b");

    SetPerfLevel(kDisable);
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddDeletion("a");
    internal_iter->AddPut("a", "val_a");

    internal_iter->AddPut("b", "val_b");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));

    db_iter->SeekToFirst();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "val_a");

    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");

    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "val_a");

    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");

    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("b", "val_b");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        2, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddPut("a", "val_a");

    internal_iter->AddPut("b", "val_b");

    internal_iter->AddPut("c", "val_c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "val_c");

    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val_b");

    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "val_c");
  }
}

TEST_F(DBIteratorTest, DBIteratorEmpty) {
  Options options;

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        0, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        0, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToFirst();
    ASSERT_TRUE(!db_iter->Valid());
  }
}

TEST_F(DBIteratorTest, DBIteratorUseSkipCountSkips) {
  Options options;
  options.statistics = rocksdb::CreateDBStatistics();
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  for (size_t i = 0; i < 200; ++i) {
    internal_iter->AddPut("a", "a");
    internal_iter->AddPut("b", "b");
    internal_iter->AddPut("c", "c");
  }
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 2,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToLast();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "c");
  ASSERT_EQ(db_iter->value().ToString(), "c");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 1u);

  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  ASSERT_EQ(db_iter->value().ToString(), "b");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 2u);

  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "a");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 3u);

  db_iter->Prev();
  ASSERT_TRUE(!db_iter->Valid());
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 3u);
}

TEST_F(DBIteratorTest, DBIteratorUseSkip) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");
  {
    for (size_t i = 0; i < 200; ++i) {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      internal_iter->AddMerge("b", "merge_1");
      internal_iter->AddMerge("a", "merge_2");
      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddPut("c", ToString(k));
      }
      internal_iter->Finish();

      options.statistics = rocksdb::CreateDBStatistics();
      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, i + 2, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "c");
      ASSERT_EQ(db_iter->value().ToString(), ToString(i));
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "b");
      ASSERT_EQ(db_iter->value().ToString(), "merge_1");
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "a");
      ASSERT_EQ(db_iter->value().ToString(), "merge_2");
      db_iter->Prev();

      ASSERT_TRUE(!db_iter->Valid());
    }
  }

  {
    for (size_t i = 0; i < 200; ++i) {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      internal_iter->AddMerge("b", "merge_1");
      internal_iter->AddMerge("a", "merge_2");
      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddDeletion("c");
      }
      internal_iter->AddPut("c", "200");
      internal_iter->Finish();

      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, i + 2, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "b");
      ASSERT_EQ(db_iter->value().ToString(), "merge_1");
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "a");
      ASSERT_EQ(db_iter->value().ToString(), "merge_2");
      db_iter->Prev();

      ASSERT_TRUE(!db_iter->Valid());
    }

    {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      internal_iter->AddMerge("b", "merge_1");
      internal_iter->AddMerge("a", "merge_2");
      for (size_t i = 0; i < 200; ++i) {
        internal_iter->AddDeletion("c");
      }
      internal_iter->AddPut("c", "200");
      internal_iter->Finish();

      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, 202, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "c");
      ASSERT_EQ(db_iter->value().ToString(), "200");
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "b");
      ASSERT_EQ(db_iter->value().ToString(), "merge_1");
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "a");
      ASSERT_EQ(db_iter->value().ToString(), "merge_2");
      db_iter->Prev();

      ASSERT_TRUE(!db_iter->Valid());
    }
  }

  {
    for (size_t i = 0; i < 200; ++i) {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddDeletion("c");
      }
      internal_iter->AddPut("c", "200");
      internal_iter->Finish();
      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, i, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(!db_iter->Valid());

      db_iter->SeekToFirst();
      ASSERT_TRUE(!db_iter->Valid());
    }

    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    for (size_t i = 0; i < 200; ++i) {
      internal_iter->AddDeletion("c");
    }
    internal_iter->AddPut("c", "200");
    internal_iter->Finish();
    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        200, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "200");

    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());

    db_iter->SeekToFirst();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "200");

    db_iter->Next();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    for (size_t i = 0; i < 200; ++i) {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      internal_iter->AddMerge("b", "merge_1");
      internal_iter->AddMerge("a", "merge_2");
      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddPut("d", ToString(k));
      }

      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddPut("c", ToString(k));
      }
      internal_iter->Finish();

      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, i + 2, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "d");
      ASSERT_EQ(db_iter->value().ToString(), ToString(i));
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "b");
      ASSERT_EQ(db_iter->value().ToString(), "merge_1");
      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "a");
      ASSERT_EQ(db_iter->value().ToString(), "merge_2");
      db_iter->Prev();

      ASSERT_TRUE(!db_iter->Valid());
    }
  }

  {
    for (size_t i = 0; i < 200; ++i) {
      TestIterator* internal_iter = new TestIterator(BytewiseComparator());
      internal_iter->AddMerge("b", "b");
      internal_iter->AddMerge("a", "a");
      for (size_t k = 0; k < 200; ++k) {
        internal_iter->AddMerge("c", ToString(k));
      }
      internal_iter->Finish();

      std::unique_ptr<Iterator> db_iter(NewDBIterator(
          env_, ImmutableCFOptions(options), BytewiseComparator(),
          internal_iter, i + 2, options.max_sequential_skip_in_iterations, 0));
      db_iter->SeekToLast();
      ASSERT_TRUE(db_iter->Valid());

      ASSERT_EQ(db_iter->key().ToString(), "c");
      std::string merge_result = "0";
      for (size_t j = 1; j <= i; ++j) {
        merge_result += "," + ToString(j);
      }
      ASSERT_EQ(db_iter->value().ToString(), merge_result);

      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());
      ASSERT_EQ(db_iter->key().ToString(), "b");
      ASSERT_EQ(db_iter->value().ToString(), "b");

      db_iter->Prev();
      ASSERT_TRUE(db_iter->Valid());
      ASSERT_EQ(db_iter->key().ToString(), "a");
      ASSERT_EQ(db_iter->value().ToString(), "a");

      db_iter->Prev();
      ASSERT_TRUE(!db_iter->Valid());
    }
  }
}

TEST_F(DBIteratorTest, DBIterator1) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->AddDeletion("b");
  internal_iter->AddMerge("a", "1");
  internal_iter->AddMerge("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 1,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0");
  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  db_iter->Next();
  ASSERT_FALSE(db_iter->Valid());
}

TEST_F(DBIteratorTest, DBIterator2) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->AddDeletion("b");
  internal_iter->AddMerge("a", "1");
  internal_iter->AddMerge("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 0,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0");
  db_iter->Next();
  ASSERT_TRUE(!db_iter->Valid());
}

TEST_F(DBIteratorTest, DBIterator3) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->AddDeletion("b");
  internal_iter->AddMerge("a", "1");
  internal_iter->AddMerge("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 2,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0");
  db_iter->Next();
  ASSERT_TRUE(!db_iter->Valid());
}
TEST_F(DBIteratorTest, DBIterator4) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->AddDeletion("b");
  internal_iter->AddMerge("a", "1");
  internal_iter->AddMerge("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 4,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0,1");
  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  ASSERT_EQ(db_iter->value().ToString(), "2");
  db_iter->Next();
  ASSERT_TRUE(!db_iter->Valid());
}

TEST_F(DBIteratorTest, DBIterator5) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        0, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        1, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1,merge_2");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        2, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1,merge_2,merge_3");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        3, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "put_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        4, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "put_1,merge_4");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        5, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "put_1,merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddPut("a", "put_1");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        6, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "put_1,merge_4,merge_5,merge_6");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    // put, singledelete, merge
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddPut("a", "val_a");
    internal_iter->AddSingleDeletion("a");
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddPut("b", "val_b");
    internal_iter->Finish();
    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));
    db_iter->Seek("b");
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
  }
}

TEST_F(DBIteratorTest, DBIterator6) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        0, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        1, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1,merge_2");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        2, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1,merge_2,merge_3");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        3, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        4, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        5, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("a", "merge_3");
    internal_iter->AddDeletion("a");
    internal_iter->AddMerge("a", "merge_4");
    internal_iter->AddMerge("a", "merge_5");
    internal_iter->AddMerge("a", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        6, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5,merge_6");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }
}

TEST_F(DBIteratorTest, DBIterator7) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        0, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        2, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "val,merge_2");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        4, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        5, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4");
    db_iter->Prev();

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        6, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        7, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        9, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_6,merge_7");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        13, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "c");
    ASSERT_EQ(db_iter->value().ToString(), "merge_4,merge_5");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(),
              "merge_6,merge_7,merge_8,merge_9,merge_10,merge_11");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }

  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddPut("b", "val");
    internal_iter->AddMerge("b", "merge_2");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_3");

    internal_iter->AddMerge("c", "merge_4");
    internal_iter->AddMerge("c", "merge_5");

    internal_iter->AddDeletion("b");
    internal_iter->AddMerge("b", "merge_6");
    internal_iter->AddMerge("b", "merge_7");
    internal_iter->AddMerge("b", "merge_8");
    internal_iter->AddMerge("b", "merge_9");
    internal_iter->AddMerge("b", "merge_10");
    internal_iter->AddMerge("b", "merge_11");

    internal_iter->AddDeletion("c");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        14, options.max_sequential_skip_in_iterations, 0));
    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(),
              "merge_6,merge_7,merge_8,merge_9,merge_10,merge_11");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());

    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1");
    db_iter->Prev();
    ASSERT_TRUE(!db_iter->Valid());
  }
}

TEST_F(DBIteratorTest, DBIterator8) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddDeletion("a");
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
      10, options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToLast();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  ASSERT_EQ(db_iter->value().ToString(), "0");

  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0");
}

// TODO(3.13): fix the issue of Seek() then Prev() which might not necessary
//             return the biggest element smaller than the seek key.
TEST_F(DBIteratorTest, DBIterator9) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");
  {
    TestIterator* internal_iter = new TestIterator(BytewiseComparator());
    internal_iter->AddMerge("a", "merge_1");
    internal_iter->AddMerge("a", "merge_2");
    internal_iter->AddMerge("b", "merge_3");
    internal_iter->AddMerge("b", "merge_4");
    internal_iter->AddMerge("d", "merge_5");
    internal_iter->AddMerge("d", "merge_6");
    internal_iter->Finish();

    std::unique_ptr<Iterator> db_iter(NewDBIterator(
        env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
        10, options.max_sequential_skip_in_iterations, 0));

    db_iter->SeekToLast();
    ASSERT_TRUE(db_iter->Valid());
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3,merge_4");
    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");
    ASSERT_EQ(db_iter->value().ToString(), "merge_5,merge_6");

    db_iter->Seek("b");
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3,merge_4");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "a");
    ASSERT_EQ(db_iter->value().ToString(), "merge_1,merge_2");

    db_iter->SeekForPrev("b");
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3,merge_4");
    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");
    ASSERT_EQ(db_iter->value().ToString(), "merge_5,merge_6");

    db_iter->Seek("c");
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");
    ASSERT_EQ(db_iter->value().ToString(), "merge_5,merge_6");
    db_iter->Prev();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3,merge_4");

    db_iter->SeekForPrev("c");
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "b");
    ASSERT_EQ(db_iter->value().ToString(), "merge_3,merge_4");
    db_iter->Next();
    ASSERT_TRUE(db_iter->Valid());
    ASSERT_EQ(db_iter->key().ToString(), "d");
    ASSERT_EQ(db_iter->value().ToString(), "merge_5,merge_6");
  }
}

// TODO(3.13): fix the issue of Seek() then Prev() which might not necessary
//             return the biggest element smaller than the seek key.
TEST_F(DBIteratorTest, DBIterator10) {
  Options options;

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "1");
  internal_iter->AddPut("b", "2");
  internal_iter->AddPut("c", "3");
  internal_iter->AddPut("d", "4");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter,
      10, options.max_sequential_skip_in_iterations, 0));

  db_iter->Seek("c");
  ASSERT_TRUE(db_iter->Valid());
  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  ASSERT_EQ(db_iter->value().ToString(), "2");

  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "c");
  ASSERT_EQ(db_iter->value().ToString(), "3");

  db_iter->SeekForPrev("c");
  ASSERT_TRUE(db_iter->Valid());
  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "d");
  ASSERT_EQ(db_iter->value().ToString(), "4");

  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "c");
  ASSERT_EQ(db_iter->value().ToString(), "3");
}

TEST_F(DBIteratorTest, SeekToLastOccurrenceSeq0) {
  Options options;
  options.merge_operator = nullptr;

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "1");
  internal_iter->AddPut("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(
      NewDBIterator(env_, ImmutableCFOptions(options), BytewiseComparator(),
                    internal_iter, 10, 0 /* force seek */, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "1");
  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  ASSERT_EQ(db_iter->value().ToString(), "2");
  db_iter->Next();
  ASSERT_FALSE(db_iter->Valid());
}

TEST_F(DBIteratorTest, DBIterator11) {
  Options options;
  options.merge_operator = MergeOperators::CreateFromStringId("stringappend");

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "0");
  internal_iter->AddPut("b", "0");
  internal_iter->AddSingleDeletion("b");
  internal_iter->AddMerge("a", "1");
  internal_iter->AddMerge("b", "2");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(NewDBIterator(
      env_, ImmutableCFOptions(options), BytewiseComparator(), internal_iter, 1,
      options.max_sequential_skip_in_iterations, 0));
  db_iter->SeekToFirst();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "0");
  db_iter->Next();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "b");
  db_iter->Next();
  ASSERT_FALSE(db_iter->Valid());
}

TEST_F(DBIteratorTest, DBIterator12) {
  Options options;
  options.merge_operator = nullptr;

  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
  internal_iter->AddPut("a", "1");
  internal_iter->AddPut("b", "2");
  internal_iter->AddPut("c", "3");
  internal_iter->AddSingleDeletion("b");
  internal_iter->Finish();

  std::unique_ptr<Iterator> db_iter(
      NewDBIterator(env_, ImmutableCFOptions(options), BytewiseComparator(),
                    internal_iter, 10, 0, 0));
  db_iter->SeekToLast();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "c");
  ASSERT_EQ(db_iter->value().ToString(), "3");
  db_iter->Prev();
  ASSERT_TRUE(db_iter->Valid());
  ASSERT_EQ(db_iter->key().ToString(), "a");
  ASSERT_EQ(db_iter->value().ToString(), "1");
  db_iter->Prev();
  ASSERT_FALSE(db_iter->Valid());
}

class DBIterWithMergeIterTest : public testing::Test {
 public:
  DBIterWithMergeIterTest()
      : env_(Env::Default()), icomp_(BytewiseComparator()) {
    options_.merge_operator = nullptr;

    internal_iter1_ = new TestIterator(BytewiseComparator());
    internal_iter1_->Add("a", kTypeValue, "1", 3u);
    internal_iter1_->Add("f", kTypeValue, "2", 5u);
    internal_iter1_->Add("g", kTypeValue, "3", 7u);
    internal_iter1_->Finish();

    internal_iter2_ = new TestIterator(BytewiseComparator());
    internal_iter2_->Add("a", kTypeValue, "4", 6u);
    internal_iter2_->Add("b", kTypeValue, "5", 1u);
    internal_iter2_->Add("c", kTypeValue, "6", 2u);
    internal_iter2_->Add("d", kTypeValue, "7", 3u);
    internal_iter2_->Finish();

    std::vector<InternalIterator*> child_iters;
    child_iters.push_back(internal_iter1_);
    child_iters.push_back(internal_iter2_);
    InternalKeyComparator icomp(BytewiseComparator());
    InternalIterator* merge_iter =
        NewMergingIterator(&icomp_, &child_iters[0], 2u);

    db_iter_.reset(NewDBIterator(env_, ImmutableCFOptions(options_),
                                 BytewiseComparator(), merge_iter,
                                 8 /* read data earlier than seqId 8 */,
                                 3 /* max iterators before reseek */, 0));
  }

  Env* env_;
  Options options_;
  TestIterator* internal_iter1_;
  TestIterator* internal_iter2_;
  InternalKeyComparator icomp_;
  Iterator* merge_iter_;
  std::unique_ptr<Iterator> db_iter_;
};

TEST_F(DBIterWithMergeIterTest, InnerMergeIterator1) {
  db_iter_->SeekToFirst();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");
  db_iter_->Next();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Next();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Next();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Next();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Next();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");
  db_iter_->Next();
  ASSERT_FALSE(db_iter_->Valid());
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIterator2) {
  // Test Prev() when one child iterator is at its end.
  db_iter_->SeekForPrev("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace1) {
  // Test Prev() when one child iterator is at its end but more rows
  // are added.
  db_iter_->Seek("f");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");

  // Test call back inserts a key in the end of the mem table after
  // MergeIterator::Prev() realized the mem table iterator is at its end
  // and before an SeekToLast() is called.
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforeSeekToLast",
      [&](void* arg) { internal_iter2_->Add("z", kTypeValue, "7", 12u); });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace2) {
  // Test Prev() when one child iterator is at its end but more rows
  // are added.
  db_iter_->Seek("f");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");

  // Test call back inserts entries for update a key in the end of the
  // mem table after MergeIterator::Prev() realized the mem tableiterator is at
  // its end and before an SeekToLast() is called.
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforeSeekToLast", [&](void* arg) {
        internal_iter2_->Add("z", kTypeValue, "7", 12u);
        internal_iter2_->Add("z", kTypeValue, "7", 11u);
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace3) {
  // Test Prev() when one child iterator is at its end but more rows
  // are added and max_skipped is triggered.
  db_iter_->Seek("f");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");

  // Test call back inserts entries for update a key in the end of the
  // mem table after MergeIterator::Prev() realized the mem table iterator is at
  // its end and before an SeekToLast() is called.
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforeSeekToLast", [&](void* arg) {
        internal_iter2_->Add("z", kTypeValue, "7", 16u, true);
        internal_iter2_->Add("z", kTypeValue, "7", 15u, true);
        internal_iter2_->Add("z", kTypeValue, "7", 14u, true);
        internal_iter2_->Add("z", kTypeValue, "7", 13u, true);
        internal_iter2_->Add("z", kTypeValue, "7", 12u, true);
        internal_iter2_->Add("z", kTypeValue, "7", 11u, true);
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace4) {
  // Test Prev() when one child iterator has more rows inserted
  // between Seek() and Prev() when changing directions.
  internal_iter2_->Add("z", kTypeValue, "9", 4u);

  db_iter_->Seek("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");

  // Test call back inserts entries for update a key before "z" in
  // mem table after MergeIterator::Prev() calls mem table iterator's
  // Seek() and before calling Prev()
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforePrev", [&](void* arg) {
        IteratorWrapper* it = reinterpret_cast<IteratorWrapper*>(arg);
        if (it->key().starts_with("z")) {
          internal_iter2_->Add("x", kTypeValue, "7", 16u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 15u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 14u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 13u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 12u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 11u, true);
        }
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace5) {
  internal_iter2_->Add("z", kTypeValue, "9", 4u);

  // Test Prev() when one child iterator has more rows inserted
  // between Seek() and Prev() when changing directions.
  db_iter_->Seek("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");

  // Test call back inserts entries for update a key before "z" in
  // mem table after MergeIterator::Prev() calls mem table iterator's
  // Seek() and before calling Prev()
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforePrev", [&](void* arg) {
        IteratorWrapper* it = reinterpret_cast<IteratorWrapper*>(arg);
        if (it->key().starts_with("z")) {
          internal_iter2_->Add("x", kTypeValue, "7", 16u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 15u, true);
        }
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace6) {
  internal_iter2_->Add("z", kTypeValue, "9", 4u);

  // Test Prev() when one child iterator has more rows inserted
  // between Seek() and Prev() when changing directions.
  db_iter_->Seek("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");

  // Test call back inserts an entry for update a key before "z" in
  // mem table after MergeIterator::Prev() calls mem table iterator's
  // Seek() and before calling Prev()
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforePrev", [&](void* arg) {
        IteratorWrapper* it = reinterpret_cast<IteratorWrapper*>(arg);
        if (it->key().starts_with("z")) {
          internal_iter2_->Add("x", kTypeValue, "7", 16u, true);
        }
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace7) {
  internal_iter1_->Add("u", kTypeValue, "10", 4u);
  internal_iter1_->Add("v", kTypeValue, "11", 4u);
  internal_iter1_->Add("w", kTypeValue, "12", 4u);
  internal_iter2_->Add("z", kTypeValue, "9", 4u);

  // Test Prev() when one child iterator has more rows inserted
  // between Seek() and Prev() when changing directions.
  db_iter_->Seek("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");

  // Test call back inserts entries for update a key before "z" in
  // mem table after MergeIterator::Prev() calls mem table iterator's
  // Seek() and before calling Prev()
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforePrev", [&](void* arg) {
        IteratorWrapper* it = reinterpret_cast<IteratorWrapper*>(arg);
        if (it->key().starts_with("z")) {
          internal_iter2_->Add("x", kTypeValue, "7", 16u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 15u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 14u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 13u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 12u, true);
          internal_iter2_->Add("x", kTypeValue, "7", 11u, true);
        }
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "c");
  ASSERT_EQ(db_iter_->value().ToString(), "6");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "b");
  ASSERT_EQ(db_iter_->value().ToString(), "5");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "a");
  ASSERT_EQ(db_iter_->value().ToString(), "4");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}

TEST_F(DBIterWithMergeIterTest, InnerMergeIteratorDataRace8) {
  // internal_iter1_: a, f, g
  // internal_iter2_: a, b, c, d, adding (z)
  internal_iter2_->Add("z", kTypeValue, "9", 4u);

  // Test Prev() when one child iterator has more rows inserted
  // between Seek() and Prev() when changing directions.
  db_iter_->Seek("g");
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "g");
  ASSERT_EQ(db_iter_->value().ToString(), "3");

  // Test call back inserts two keys before "z" in mem table after
  // MergeIterator::Prev() calls mem table iterator's Seek() and
  // before calling Prev()
  rocksdb::SyncPoint::GetInstance()->SetCallBack(
      "MergeIterator::Prev:BeforePrev", [&](void* arg) {
        IteratorWrapper* it = reinterpret_cast<IteratorWrapper*>(arg);
        if (it->key().starts_with("z")) {
          internal_iter2_->Add("x", kTypeValue, "7", 16u, true);
          internal_iter2_->Add("y", kTypeValue, "7", 17u, true);
        }
      });
  rocksdb::SyncPoint::GetInstance()->EnableProcessing();

  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "f");
  ASSERT_EQ(db_iter_->value().ToString(), "2");
  db_iter_->Prev();
  ASSERT_TRUE(db_iter_->Valid());
  ASSERT_EQ(db_iter_->key().ToString(), "d");
  ASSERT_EQ(db_iter_->value().ToString(), "7");

  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}
}  // namespace rocksdb

int main(int argc, char** argv) {
  ::testing::InitGoogleTest(&argc, argv);
  return RUN_ALL_TESTS();
}