text: //  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).
  
  #ifndef ROCKSDB_LITE
  
  #ifndef GFLAGS
  #include <cstdio>
  int main() {
    fprintf(stderr, "Please install gflags to run this test... Skipping...\n");
    return 0;
  }
  #else
  
  #include <algorithm>
  #include <iostream>
  #include <vector>
  
  #include "db/db_impl.h"
  #include "monitoring/histogram.h"
  #include "rocksdb/comparator.h"
  #include "rocksdb/db.h"
  #include "rocksdb/filter_policy.h"
  #include "rocksdb/memtablerep.h"
  #include "rocksdb/perf_context.h"
  #include "rocksdb/slice_transform.h"
  #include "rocksdb/table.h"
  #include "util/coding.h"
  #include "util/gflags_compat.h"
  #include "util/random.h"
  #include "util/stop_watch.h"
  #include "util/string_util.h"
  #include "util/testharness.h"
  #include "utilities/merge_operators.h"
  
  using GFLAGS_NAMESPACE::ParseCommandLineFlags;
  
  DEFINE_bool(trigger_deadlock, false,
              "issue delete in range scan to trigger PrefixHashMap deadlock");
  DEFINE_int32(bucket_count, 100000, "number of buckets");
  DEFINE_uint64(num_locks, 10001, "number of locks");
  DEFINE_bool(random_prefix, false, "randomize prefix");
  DEFINE_uint64(total_prefixes, 100000, "total number of prefixes");
  DEFINE_uint64(items_per_prefix, 1, "total number of values per prefix");
  DEFINE_int64(write_buffer_size, 33554432, "");
  DEFINE_int32(max_write_buffer_number, 2, "");
  DEFINE_int32(min_write_buffer_number_to_merge, 1, "");
  DEFINE_int32(skiplist_height, 4, "");
  DEFINE_double(memtable_prefix_bloom_size_ratio, 0.1, "");
  DEFINE_int32(memtable_huge_page_size, 2 * 1024 * 1024, "");
  DEFINE_int32(value_size, 40, "");
  DEFINE_bool(enable_print, false, "Print options generated to console.");
  
  // Path to the database on file system
  const std::string kDbName = rocksdb::test::PerThreadDBPath("prefix_test");
  
  namespace rocksdb {
  
  struct TestKey {
    uint64_t prefix;
    uint64_t sorted;
  
    TestKey(uint64_t _prefix, uint64_t _sorted)
        : prefix(_prefix), sorted(_sorted) {}
  };
  
  // return a slice backed by test_key
  inline Slice TestKeyToSlice(std::string &s, const TestKey& test_key) {
    s.clear();
    PutFixed64(&s, test_key.prefix);
    PutFixed64(&s, test_key.sorted);
    return Slice(s.c_str(), s.size());
  }
  
  inline const TestKey SliceToTestKey(const Slice& slice) {
    return TestKey(DecodeFixed64(slice.data()),
      DecodeFixed64(slice.data() + 8));
  }
  
  class TestKeyComparator : public Comparator {
   public:
  
    // Compare needs to be aware of the possibility of a and/or b is
    // prefix only
    int Compare(const Slice& a, const Slice& b) const override {
      const TestKey kkey_a = SliceToTestKey(a);
      const TestKey kkey_b = SliceToTestKey(b);
      const TestKey *key_a = &kkey_a;
      const TestKey *key_b = &kkey_b;
      if (key_a->prefix != key_b->prefix) {
        if (key_a->prefix < key_b->prefix) return -1;
        if (key_a->prefix > key_b->prefix) return 1;
      } else {
        EXPECT_TRUE(key_a->prefix == key_b->prefix);
        // note, both a and b could be prefix only
        if (a.size() != b.size()) {
          // one of them is prefix
          EXPECT_TRUE(
              (a.size() == sizeof(uint64_t) && b.size() == sizeof(TestKey)) ||
              (b.size() == sizeof(uint64_t) && a.size() == sizeof(TestKey)));
          if (a.size() < b.size()) return -1;
          if (a.size() > b.size()) return 1;
        } else {
          // both a and b are prefix
          if (a.size() == sizeof(uint64_t)) {
            return 0;
          }
  
          // both a and b are whole key
          EXPECT_TRUE(a.size() == sizeof(TestKey) && b.size() == sizeof(TestKey));
          if (key_a->sorted < key_b->sorted) return -1;
          if (key_a->sorted > key_b->sorted) return 1;
          if (key_a->sorted == key_b->sorted) return 0;
        }
      }
      return 0;
    }
  
    bool operator()(const TestKey& a, const TestKey& b) const {
      std::string sa, sb;
      return Compare(TestKeyToSlice(sa, a), TestKeyToSlice(sb, b)) < 0;
    }
  
    const char* Name() const override { return "TestKeyComparator"; }
  
    void FindShortestSeparator(std::string* /*start*/,
                               const Slice& /*limit*/) const override {}
  
    void FindShortSuccessor(std::string* /*key*/) const override {}
  };
  
  namespace {
  void PutKey(DB* db, WriteOptions write_options, uint64_t prefix,
              uint64_t suffix, const Slice& value) {
    TestKey test_key(prefix, suffix);
    std::string s;
    Slice key = TestKeyToSlice(s, test_key);
    ASSERT_OK(db->Put(write_options, key, value));
  }
  
  void PutKey(DB* db, WriteOptions write_options, const TestKey& test_key,
              const Slice& value) {
    std::string s;
    Slice key = TestKeyToSlice(s, test_key);
    ASSERT_OK(db->Put(write_options, key, value));
  }
  
  void MergeKey(DB* db, WriteOptions write_options, const TestKey& test_key,
                const Slice& value) {
    std::string s;
    Slice key = TestKeyToSlice(s, test_key);
    ASSERT_OK(db->Merge(write_options, key, value));
  }
  
  void DeleteKey(DB* db, WriteOptions write_options, const TestKey& test_key) {
    std::string s;
    Slice key = TestKeyToSlice(s, test_key);
    ASSERT_OK(db->Delete(write_options, key));
  }
  
  void SeekIterator(Iterator* iter, uint64_t prefix, uint64_t suffix) {
    TestKey test_key(prefix, suffix);
    std::string s;
    Slice key = TestKeyToSlice(s, test_key);
    iter->Seek(key);
  }
  
  const std::string kNotFoundResult = "NOT_FOUND";
  
  std::string Get(DB* db, const ReadOptions& read_options, uint64_t prefix,
                  uint64_t suffix) {
    TestKey test_key(prefix, suffix);
    std::string s2;
    Slice key = TestKeyToSlice(s2, test_key);
  
    std::string result;
    Status s = db->Get(read_options, key, &result);
    if (s.IsNotFound()) {
      result = kNotFoundResult;
    } else if (!s.ok()) {
      result = s.ToString();
    }
    return result;
  }
  
  class SamePrefixTransform : public SliceTransform {
   private:
    const Slice prefix_;
    std::string name_;
  
   public:
    explicit SamePrefixTransform(const Slice& prefix)
        : prefix_(prefix), name_("rocksdb.SamePrefix." + prefix.ToString()) {}
  
    const char* Name() const override { return name_.c_str(); }
  
    Slice Transform(const Slice& src) const override {
      assert(InDomain(src));
      return prefix_;
    }
  
    bool InDomain(const Slice& src) const override {
      if (src.size() >= prefix_.size()) {
        return Slice(src.data(), prefix_.size()) == prefix_;
      }
      return false;
    }
  
    bool InRange(const Slice& dst) const override { return dst == prefix_; }
  
    bool FullLengthEnabled(size_t* /*len*/) const override { return false; }
  };
  
  }  // namespace
  
  class PrefixTest : public testing::Test {
   public:
    std::shared_ptr<DB> OpenDb() {
      DB* db;
  
      options.create_if_missing = true;
      options.write_buffer_size = FLAGS_write_buffer_size;
      options.max_write_buffer_number = FLAGS_max_write_buffer_number;
      options.min_write_buffer_number_to_merge =
        FLAGS_min_write_buffer_number_to_merge;
  
      options.memtable_prefix_bloom_size_ratio =
          FLAGS_memtable_prefix_bloom_size_ratio;
      options.memtable_huge_page_size = FLAGS_memtable_huge_page_size;
  
      options.prefix_extractor.reset(NewFixedPrefixTransform(8));
      BlockBasedTableOptions bbto;
      bbto.filter_policy.reset(NewBloomFilterPolicy(10, false));
      bbto.whole_key_filtering = false;
      options.table_factory.reset(NewBlockBasedTableFactory(bbto));
      options.allow_concurrent_memtable_write = false;
  
      Status s = DB::Open(options, kDbName,  &db);
      EXPECT_OK(s);
      return std::shared_ptr<DB>(db);
    }
  
    void FirstOption() {
      option_config_ = kBegin;
    }
  
    bool NextOptions(int bucket_count) {
      // skip some options
      option_config_++;
      if (option_config_ < kEnd) {
        options.prefix_extractor.reset(NewFixedPrefixTransform(8));
        switch(option_config_) {
          case kHashSkipList:
            options.memtable_factory.reset(
                NewHashSkipListRepFactory(bucket_count, FLAGS_skiplist_height));
            return true;
          case kHashLinkList:
            options.memtable_factory.reset(
                NewHashLinkListRepFactory(bucket_count));
            return true;
          case kHashLinkListHugePageTlb:
            options.memtable_factory.reset(
                NewHashLinkListRepFactory(bucket_count, 2 * 1024 * 1024));
            return true;
          case kHashLinkListTriggerSkipList:
            options.memtable_factory.reset(
                NewHashLinkListRepFactory(bucket_count, 0, 3));
            return true;
          default:
            return false;
        }
      }
      return false;
    }
  
    PrefixTest() : option_config_(kBegin) {
      options.comparator = new TestKeyComparator();
    }
    ~PrefixTest() override { delete options.comparator; }
  
   protected:
    enum OptionConfig {
      kBegin,
      kHashSkipList,
      kHashLinkList,
      kHashLinkListHugePageTlb,
      kHashLinkListTriggerSkipList,
      kEnd
    };
    int option_config_;
    Options options;
  };
  
  TEST(SamePrefixTest, InDomainTest) {
    DB* db;
    Options options;
    options.create_if_missing = true;
    options.prefix_extractor.reset(new SamePrefixTransform("HHKB"));
    BlockBasedTableOptions bbto;
    bbto.filter_policy.reset(NewBloomFilterPolicy(10, false));
    bbto.whole_key_filtering = false;
    options.table_factory.reset(NewBlockBasedTableFactory(bbto));
    WriteOptions write_options;
    ReadOptions read_options;
    {
      ASSERT_OK(DestroyDB(kDbName, Options()));
      ASSERT_OK(DB::Open(options, kDbName, &db));
      ASSERT_OK(db->Put(write_options, "HHKB pro2", "Mar 24, 2006"));
      ASSERT_OK(db->Put(write_options, "HHKB pro2 Type-S", "June 29, 2011"));
      ASSERT_OK(db->Put(write_options, "Realforce 87u", "idk"));
      db->Flush(FlushOptions());
      std::string result;
      auto db_iter = db->NewIterator(ReadOptions());
  
      db_iter->Seek("Realforce 87u");
      ASSERT_TRUE(db_iter->Valid());
      ASSERT_OK(db_iter->status());
      ASSERT_EQ(db_iter->key(), "Realforce 87u");
      ASSERT_EQ(db_iter->value(), "idk");
  
      delete db_iter;
      delete db;
      ASSERT_OK(DestroyDB(kDbName, Options()));
    }
  
    {
      ASSERT_OK(DB::Open(options, kDbName, &db));
      ASSERT_OK(db->Put(write_options, "pikachu", "1"));
      ASSERT_OK(db->Put(write_options, "Meowth", "1"));
      ASSERT_OK(db->Put(write_options, "Mewtwo", "idk"));
      db->Flush(FlushOptions());
      std::string result;
      auto db_iter = db->NewIterator(ReadOptions());
  
      db_iter->Seek("Mewtwo");
      ASSERT_TRUE(db_iter->Valid());
      ASSERT_OK(db_iter->status());
      delete db_iter;
      delete db;
      ASSERT_OK(DestroyDB(kDbName, Options()));
    }
  }
  
  TEST_F(PrefixTest, TestResult) {
    for (int num_buckets = 1; num_buckets <= 2; num_buckets++) {
      FirstOption();
      while (NextOptions(num_buckets)) {
        std::cout << "*** Mem table: " << options.memtable_factory->Name()
                  << " number of buckets: " << num_buckets
                  << std::endl;
        DestroyDB(kDbName, Options());
        auto db = OpenDb();
        WriteOptions write_options;
        ReadOptions read_options;
  
        // 1. Insert one row.
        Slice v16("v16");
        PutKey(db.get(), write_options, 1, 6, v16);
        std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
        SeekIterator(iter.get(), 1, 6);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        iter->Next();
        ASSERT_TRUE(!iter->Valid());
  
        SeekIterator(iter.get(), 2, 0);
        ASSERT_TRUE(!iter->Valid());
  
        ASSERT_EQ(v16.ToString(), Get(db.get(), read_options, 1, 6));
        ASSERT_EQ(kNotFoundResult, Get(db.get(), read_options, 1, 5));
        ASSERT_EQ(kNotFoundResult, Get(db.get(), read_options, 1, 7));
        ASSERT_EQ(kNotFoundResult, Get(db.get(), read_options, 0, 6));
        ASSERT_EQ(kNotFoundResult, Get(db.get(), read_options, 2, 6));
  
        // 2. Insert an entry for the same prefix as the last entry in the bucket.
        Slice v17("v17");
        PutKey(db.get(), write_options, 1, 7, v17);
        iter.reset(db->NewIterator(read_options));
        SeekIterator(iter.get(), 1, 7);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        SeekIterator(iter.get(), 1, 6);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
        iter->Next();
        ASSERT_TRUE(!iter->Valid());
  
        SeekIterator(iter.get(), 2, 0);
        ASSERT_TRUE(!iter->Valid());
  
        // 3. Insert an entry for the same prefix as the head of the bucket.
        Slice v15("v15");
        PutKey(db.get(), write_options, 1, 5, v15);
        iter.reset(db->NewIterator(read_options));
  
        SeekIterator(iter.get(), 1, 7);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v15 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v15 == iter->value());
  
        ASSERT_EQ(v15.ToString(), Get(db.get(), read_options, 1, 5));
        ASSERT_EQ(v16.ToString(), Get(db.get(), read_options, 1, 6));
        ASSERT_EQ(v17.ToString(), Get(db.get(), read_options, 1, 7));
  
        // 4. Insert an entry with a larger prefix
        Slice v22("v22");
        PutKey(db.get(), write_options, 2, 2, v22);
        iter.reset(db->NewIterator(read_options));
  
        SeekIterator(iter.get(), 2, 2);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v22 == iter->value());
        SeekIterator(iter.get(), 2, 0);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v22 == iter->value());
  
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v15 == iter->value());
  
        SeekIterator(iter.get(), 1, 7);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        // 5. Insert an entry with a smaller prefix
        Slice v02("v02");
        PutKey(db.get(), write_options, 0, 2, v02);
        iter.reset(db->NewIterator(read_options));
  
        SeekIterator(iter.get(), 0, 2);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v02 == iter->value());
        SeekIterator(iter.get(), 0, 0);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v02 == iter->value());
  
        SeekIterator(iter.get(), 2, 0);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v22 == iter->value());
  
        SeekIterator(iter.get(), 1, 5);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v15 == iter->value());
  
        SeekIterator(iter.get(), 1, 7);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        // 6. Insert to the beginning and the end of the first prefix
        Slice v13("v13");
        Slice v18("v18");
        PutKey(db.get(), write_options, 1, 3, v13);
        PutKey(db.get(), write_options, 1, 8, v18);
        iter.reset(db->NewIterator(read_options));
        SeekIterator(iter.get(), 1, 7);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        SeekIterator(iter.get(), 1, 3);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v13 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v15 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v18 == iter->value());
  
        SeekIterator(iter.get(), 0, 0);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v02 == iter->value());
  
        SeekIterator(iter.get(), 2, 0);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v22 == iter->value());
  
        ASSERT_EQ(v22.ToString(), Get(db.get(), read_options, 2, 2));
        ASSERT_EQ(v02.ToString(), Get(db.get(), read_options, 0, 2));
        ASSERT_EQ(v13.ToString(), Get(db.get(), read_options, 1, 3));
        ASSERT_EQ(v15.ToString(), Get(db.get(), read_options, 1, 5));
        ASSERT_EQ(v16.ToString(), Get(db.get(), read_options, 1, 6));
        ASSERT_EQ(v17.ToString(), Get(db.get(), read_options, 1, 7));
        ASSERT_EQ(v18.ToString(), Get(db.get(), read_options, 1, 8));
      }
    }
  }
  
  // Show results in prefix
  TEST_F(PrefixTest, PrefixValid) {
    for (int num_buckets = 1; num_buckets <= 2; num_buckets++) {
      FirstOption();
      while (NextOptions(num_buckets)) {
        std::cout << "*** Mem table: " << options.memtable_factory->Name()
                  << " number of buckets: " << num_buckets << std::endl;
        DestroyDB(kDbName, Options());
        auto db = OpenDb();
        WriteOptions write_options;
        ReadOptions read_options;
  
        // Insert keys with common prefix and one key with different
        Slice v16("v16");
        Slice v17("v17");
        Slice v18("v18");
        Slice v19("v19");
        PutKey(db.get(), write_options, 12345, 6, v16);
        PutKey(db.get(), write_options, 12345, 7, v17);
        PutKey(db.get(), write_options, 12345, 8, v18);
        PutKey(db.get(), write_options, 12345, 9, v19);
        PutKey(db.get(), write_options, 12346, 8, v16);
        db->Flush(FlushOptions());
        TestKey test_key(12346, 8);
        std::string s;
        db->Delete(write_options, TestKeyToSlice(s, test_key));
        db->Flush(FlushOptions());
        read_options.prefix_same_as_start = true;
        std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
        SeekIterator(iter.get(), 12345, 6);
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v16 == iter->value());
  
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v17 == iter->value());
  
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v18 == iter->value());
  
        iter->Next();
        ASSERT_TRUE(iter->Valid());
        ASSERT_TRUE(v19 == iter->value());
        iter->Next();
        ASSERT_FALSE(iter->Valid());
        ASSERT_EQ(kNotFoundResult, Get(db.get(), read_options, 12346, 8));
  
        // Verify seeking past the prefix won't return a result.
        SeekIterator(iter.get(), 12345, 10);
        ASSERT_TRUE(!iter->Valid());
      }
    }
  }
  
  TEST_F(PrefixTest, DynamicPrefixIterator) {
    while (NextOptions(FLAGS_bucket_count)) {
      std::cout << "*** Mem table: " << options.memtable_factory->Name()
          << std::endl;
      DestroyDB(kDbName, Options());
      auto db = OpenDb();
      WriteOptions write_options;
      ReadOptions read_options;
  
      std::vector<uint64_t> prefixes;
      for (uint64_t i = 0; i < FLAGS_total_prefixes; ++i) {
        prefixes.push_back(i);
      }
  
      if (FLAGS_random_prefix) {
        std::random_shuffle(prefixes.begin(), prefixes.end());
      }
  
      HistogramImpl hist_put_time;
      HistogramImpl hist_put_comparison;
  
      // insert x random prefix, each with y continuous element.
      for (auto prefix : prefixes) {
         for (uint64_t sorted = 0; sorted < FLAGS_items_per_prefix; sorted++) {
          TestKey test_key(prefix, sorted);
  
          std::string s;
          Slice key = TestKeyToSlice(s, test_key);
          std::string value(FLAGS_value_size, 0);
  
          get_perf_context()->Reset();
          StopWatchNano timer(Env::Default(), true);
          ASSERT_OK(db->Put(write_options, key, value));
          hist_put_time.Add(timer.ElapsedNanos());
          hist_put_comparison.Add(get_perf_context()->user_key_comparison_count);
        }
      }
  
      std::cout << "Put key comparison: \n" << hist_put_comparison.ToString()
                << "Put time: \n" << hist_put_time.ToString();
  
      // test seek existing keys
      HistogramImpl hist_seek_time;
      HistogramImpl hist_seek_comparison;
  
      std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
  
      for (auto prefix : prefixes) {
        TestKey test_key(prefix, FLAGS_items_per_prefix / 2);
        std::string s;
        Slice key = TestKeyToSlice(s, test_key);
        std::string value = "v" + ToString(0);
  
        get_perf_context()->Reset();
        StopWatchNano timer(Env::Default(), true);
        auto key_prefix = options.prefix_extractor->Transform(key);
        uint64_t total_keys = 0;
        for (iter->Seek(key);
             iter->Valid() && iter->key().starts_with(key_prefix);
             iter->Next()) {
          if (FLAGS_trigger_deadlock) {
            std::cout << "Behold the deadlock!\n";
            db->Delete(write_options, iter->key());
          }
          total_keys++;
        }
        hist_seek_time.Add(timer.ElapsedNanos());
        hist_seek_comparison.Add(get_perf_context()->user_key_comparison_count);
        ASSERT_EQ(total_keys, FLAGS_items_per_prefix - FLAGS_items_per_prefix/2);
      }
  
      std::cout << "Seek key comparison: \n"
                << hist_seek_comparison.ToString()
                << "Seek time: \n"
                << hist_seek_time.ToString();
  
      // test non-existing keys
      HistogramImpl hist_no_seek_time;
      HistogramImpl hist_no_seek_comparison;
  
      for (auto prefix = FLAGS_total_prefixes;
           prefix < FLAGS_total_prefixes + 10000;
           prefix++) {
        TestKey test_key(prefix, 0);
        std::string s;
        Slice key = TestKeyToSlice(s, test_key);
  
        get_perf_context()->Reset();
        StopWatchNano timer(Env::Default(), true);
        iter->Seek(key);
        hist_no_seek_time.Add(timer.ElapsedNanos());
        hist_no_seek_comparison.Add(get_perf_context()->user_key_comparison_count);
        ASSERT_TRUE(!iter->Valid());
      }
  
      std::cout << "non-existing Seek key comparison: \n"
                << hist_no_seek_comparison.ToString()
                << "non-existing Seek time: \n"
                << hist_no_seek_time.ToString();
    }
  }
  
  TEST_F(PrefixTest, PrefixSeekModePrev) {
    // Only for SkipListFactory
    options.memtable_factory.reset(new SkipListFactory);
    options.merge_operator = MergeOperators::CreatePutOperator();
    options.write_buffer_size = 1024 * 1024;
    Random rnd(1);
    for (size_t m = 1; m < 100; m++) {
      std::cout << "[" + std::to_string(m) + "]" + "*** Mem table: "
                << options.memtable_factory->Name() << std::endl;
      DestroyDB(kDbName, Options());
      auto db = OpenDb();
      WriteOptions write_options;
      ReadOptions read_options;
      std::map<TestKey, std::string, TestKeyComparator> entry_maps[3], whole_map;
      for (uint64_t i = 0; i < 10; i++) {
        int div = i % 3 + 1;
        for (uint64_t j = 0; j < 10; j++) {
          whole_map[TestKey(i, j)] = entry_maps[rnd.Uniform(div)][TestKey(i, j)] =
              'v' + std::to_string(i) + std::to_string(j);
        }
      }
  
      std::map<TestKey, std::string, TestKeyComparator> type_map;
      for (size_t i = 0; i < 3; i++) {
        for (auto& kv : entry_maps[i]) {
          if (rnd.OneIn(3)) {
            PutKey(db.get(), write_options, kv.first, kv.second);
            type_map[kv.first] = "value";
          } else {
            MergeKey(db.get(), write_options, kv.first, kv.second);
            type_map[kv.first] = "merge";
          }
        }
        if (i < 2) {
          db->Flush(FlushOptions());
        }
      }
  
      for (size_t i = 0; i < 2; i++) {
        for (auto& kv : entry_maps[i]) {
          if (rnd.OneIn(10)) {
            whole_map.erase(kv.first);
            DeleteKey(db.get(), write_options, kv.first);
            entry_maps[2][kv.first] = "delete";
          }
        }
      }
  
      if (FLAGS_enable_print) {
        for (size_t i = 0; i < 3; i++) {
          for (auto& kv : entry_maps[i]) {
            std::cout << "[" << i << "]" << kv.first.prefix << kv.first.sorted
                      << " " << kv.second + " " + type_map[kv.first] << std::endl;
          }
        }
      }
  
      std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
      for (uint64_t prefix = 0; prefix < 10; prefix++) {
        uint64_t start_suffix = rnd.Uniform(9);
        SeekIterator(iter.get(), prefix, start_suffix);
        auto it = whole_map.find(TestKey(prefix, start_suffix));
        if (it == whole_map.end()) {
          continue;
        }
        ASSERT_NE(it, whole_map.end());
        ASSERT_TRUE(iter->Valid());
        if (FLAGS_enable_print) {
          std::cout << "round " << prefix
                    << " iter: " << SliceToTestKey(iter->key()).prefix
                    << SliceToTestKey(iter->key()).sorted
                    << " | map: " << it->first.prefix << it->first.sorted << " | "
                    << iter->value().ToString() << " " << it->second << std::endl;
        }
        ASSERT_EQ(iter->value(), it->second);
        uint64_t stored_prefix = prefix;
        for (size_t k = 0; k < 9; k++) {
          if (rnd.OneIn(2) || it == whole_map.begin()) {
            iter->Next();
            ++it;
            if (FLAGS_enable_print) {
              std::cout << "Next >> ";
            }
          } else {
            iter->Prev();
            it--;
            if (FLAGS_enable_print) {
              std::cout << "Prev >> ";
            }
          }
          if (!iter->Valid() ||
              SliceToTestKey(iter->key()).prefix != stored_prefix) {
            break;
          }
          stored_prefix = SliceToTestKey(iter->key()).prefix;
          ASSERT_TRUE(iter->Valid());
          ASSERT_NE(it, whole_map.end());
          ASSERT_EQ(iter->value(), it->second);
          if (FLAGS_enable_print) {
            std::cout << "iter: " << SliceToTestKey(iter->key()).prefix
                      << SliceToTestKey(iter->key()).sorted
                      << " | map: " << it->first.prefix << it->first.sorted
                      << " | " << iter->value().ToString() << " " << it->second
                      << std::endl;
          }
        }
      }
    }
  }
  
  TEST_F(PrefixTest, PrefixSeekModePrev2) {
    // Only for SkipListFactory
    // test the case
    //        iter1                iter2
    // | prefix | suffix |  | prefix | suffix |
    // |   1    |   1    |  |   1    |   2    |
    // |   1    |   3    |  |   1    |   4    |
    // |   2    |   1    |  |   3    |   3    |
    // |   2    |   2    |  |   3    |   4    |
    // after seek(15), iter1 will be at 21 and iter2 will be 33.
    // Then if call Prev() in prefix mode where SeekForPrev(21) gets called,
    // iter2 should turn to invalid state because of bloom filter.
    options.memtable_factory.reset(new SkipListFactory);
    options.write_buffer_size = 1024 * 1024;
    std::string v13("v13");
    DestroyDB(kDbName, Options());
    auto db = OpenDb();
    WriteOptions write_options;
    ReadOptions read_options;
    PutKey(db.get(), write_options, TestKey(1, 2), "v12");
    PutKey(db.get(), write_options, TestKey(1, 4), "v14");
    PutKey(db.get(), write_options, TestKey(3, 3), "v33");
    PutKey(db.get(), write_options, TestKey(3, 4), "v34");
    db->Flush(FlushOptions());
    reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
    PutKey(db.get(), write_options, TestKey(1, 1), "v11");
    PutKey(db.get(), write_options, TestKey(1, 3), "v13");
    PutKey(db.get(), write_options, TestKey(2, 1), "v21");
    PutKey(db.get(), write_options, TestKey(2, 2), "v22");
    db->Flush(FlushOptions());
    reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
    std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
    SeekIterator(iter.get(), 1, 5);
    iter->Prev();
    ASSERT_EQ(iter->value(), v13);
  }
  
  TEST_F(PrefixTest, PrefixSeekModePrev3) {
    // Only for SkipListFactory
    // test SeekToLast() with iterate_upper_bound_ in prefix_seek_mode
    options.memtable_factory.reset(new SkipListFactory);
    options.write_buffer_size = 1024 * 1024;
    std::string v14("v14");
    TestKey upper_bound_key = TestKey(1, 5);
    std::string s;
    Slice upper_bound = TestKeyToSlice(s, upper_bound_key);
  
    {
      DestroyDB(kDbName, Options());
      auto db = OpenDb();
      WriteOptions write_options;
      ReadOptions read_options;
      read_options.iterate_upper_bound = &upper_bound;
      PutKey(db.get(), write_options, TestKey(1, 2), "v12");
      PutKey(db.get(), write_options, TestKey(1, 4), "v14");
      db->Flush(FlushOptions());
      reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
      PutKey(db.get(), write_options, TestKey(1, 1), "v11");
      PutKey(db.get(), write_options, TestKey(1, 3), "v13");
      PutKey(db.get(), write_options, TestKey(2, 1), "v21");
      PutKey(db.get(), write_options, TestKey(2, 2), "v22");
      db->Flush(FlushOptions());
      reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
      std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
      iter->SeekToLast();
      ASSERT_EQ(iter->value(), v14);
    }
    {
      DestroyDB(kDbName, Options());
      auto db = OpenDb();
      WriteOptions write_options;
      ReadOptions read_options;
      read_options.iterate_upper_bound = &upper_bound;
      PutKey(db.get(), write_options, TestKey(1, 2), "v12");
      PutKey(db.get(), write_options, TestKey(1, 4), "v14");
      PutKey(db.get(), write_options, TestKey(3, 3), "v33");
      PutKey(db.get(), write_options, TestKey(3, 4), "v34");
      db->Flush(FlushOptions());
      reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
      PutKey(db.get(), write_options, TestKey(1, 1), "v11");
      PutKey(db.get(), write_options, TestKey(1, 3), "v13");
      db->Flush(FlushOptions());
      reinterpret_cast<DBImpl*>(db.get())->TEST_WaitForFlushMemTable();
      std::unique_ptr<Iterator> iter(db->NewIterator(read_options));
      iter->SeekToLast();
      ASSERT_EQ(iter->value(), v14);
    }
  }
  
  }  // end namespace rocksdb
  
  int main(int argc, char** argv) {
    ::testing::InitGoogleTest(&argc, argv);
    ParseCommandLineFlags(&argc, &argv, true);
    return RUN_ALL_TESTS();
  }
  
  #endif  // GFLAGS
  
  #else
  #include <stdio.h>
  
  int main(int /*argc*/, char** /*argv*/) {
    fprintf(stderr,
            "SKIPPED as HashSkipList and HashLinkList are not supported in "
            "ROCKSDB_LITE\n");
    return 0;
  }
  
  #endif  // !ROCKSDB_LITE
  