rocksdb/db/db_iterator_test.cc

//  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.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "db/db_test_util.h"
#include "port/stack_trace.h"
#include "rocksdb/perf_context.h"

namespace rocksdb {

class DBIteratorTest : public DBTestBase {
 public:
  DBIteratorTest() : DBTestBase("/db_iterator_test") {}
};

TEST_F(DBIteratorTest, IteratorProperty) {
  // The test needs to be changed if kPersistedTier is supported in iterator.
  Options options = CurrentOptions();
  CreateAndReopenWithCF({"pikachu"}, options);
  Put(1, "1", "2");
  ReadOptions ropt;
  ropt.pin_data = false;
  {
    unique_ptr<Iterator> iter(db_->NewIterator(ropt, handles_[1]));
    iter->SeekToFirst();
    std::string prop_value;
    ASSERT_NOK(iter->GetProperty("non_existing.value", &prop_value));
    ASSERT_OK(iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
    ASSERT_EQ("0", prop_value);
    iter->Next();
    ASSERT_OK(iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
    ASSERT_EQ("Iterator is not valid.", prop_value);
  }
  Close();
}

TEST_F(DBIteratorTest, PersistedTierOnIterator) {
  // The test needs to be changed if kPersistedTier is supported in iterator.
  Options options = CurrentOptions();
  CreateAndReopenWithCF({"pikachu"}, options);
  ReadOptions ropt;
  ropt.read_tier = kPersistedTier;

  auto* iter = db_->NewIterator(ropt, handles_[1]);
  ASSERT_TRUE(iter->status().IsNotSupported());
  delete iter;

  std::vector<Iterator*> iters;
  ASSERT_TRUE(db_->NewIterators(ropt, {handles_[1]}, &iters).IsNotSupported());
  Close();
}

TEST_F(DBIteratorTest, NonBlockingIteration) {
  do {
    ReadOptions non_blocking_opts, regular_opts;
    Options options = CurrentOptions();
    options.statistics = rocksdb::CreateDBStatistics();
    non_blocking_opts.read_tier = kBlockCacheTier;
    CreateAndReopenWithCF({"pikachu"}, options);
    // write one kv to the database.
    ASSERT_OK(Put(1, "a", "b"));

    // scan using non-blocking iterator. We should find it because
    // it is in memtable.
    Iterator* iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    int count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      ASSERT_OK(iter->status());
      count++;
    }
    ASSERT_EQ(count, 1);
    delete iter;

    // flush memtable to storage. Now, the key should not be in the
    // memtable neither in the block cache.
    ASSERT_OK(Flush(1));

    // verify that a non-blocking iterator does not find any
    // kvs. Neither does it do any IOs to storage.
    uint64_t numopen = TestGetTickerCount(options, NO_FILE_OPENS);
    uint64_t cache_added = TestGetTickerCount(options, BLOCK_CACHE_ADD);
    iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      count++;
    }
    ASSERT_EQ(count, 0);
    ASSERT_TRUE(iter->status().IsIncomplete());
    ASSERT_EQ(numopen, TestGetTickerCount(options, NO_FILE_OPENS));
    ASSERT_EQ(cache_added, TestGetTickerCount(options, BLOCK_CACHE_ADD));
    delete iter;

    // read in the specified block via a regular get
    ASSERT_EQ(Get(1, "a"), "b");

    // verify that we can find it via a non-blocking scan
    numopen = TestGetTickerCount(options, NO_FILE_OPENS);
    cache_added = TestGetTickerCount(options, BLOCK_CACHE_ADD);
    iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      ASSERT_OK(iter->status());
      count++;
    }
    ASSERT_EQ(count, 1);
    ASSERT_EQ(numopen, TestGetTickerCount(options, NO_FILE_OPENS));
    ASSERT_EQ(cache_added, TestGetTickerCount(options, BLOCK_CACHE_ADD));
    delete iter;

    // This test verifies block cache behaviors, which is not used by plain
    // table format.
    // Exclude kHashCuckoo as it does not support iteration currently
  } while (ChangeOptions(kSkipPlainTable | kSkipNoSeekToLast | kSkipHashCuckoo |
                         kSkipMmapReads));
}

#ifndef ROCKSDB_LITE
TEST_F(DBIteratorTest, ManagedNonBlockingIteration) {
  do {
    ReadOptions non_blocking_opts, regular_opts;
    Options options = CurrentOptions();
    options.statistics = rocksdb::CreateDBStatistics();
    non_blocking_opts.read_tier = kBlockCacheTier;
    non_blocking_opts.managed = true;
    CreateAndReopenWithCF({"pikachu"}, options);
    // write one kv to the database.
    ASSERT_OK(Put(1, "a", "b"));

    // scan using non-blocking iterator. We should find it because
    // it is in memtable.
    Iterator* iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    int count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      ASSERT_OK(iter->status());
      count++;
    }
    ASSERT_EQ(count, 1);
    delete iter;

    // flush memtable to storage. Now, the key should not be in the
    // memtable neither in the block cache.
    ASSERT_OK(Flush(1));

    // verify that a non-blocking iterator does not find any
    // kvs. Neither does it do any IOs to storage.
    int64_t numopen = TestGetTickerCount(options, NO_FILE_OPENS);
    int64_t cache_added = TestGetTickerCount(options, BLOCK_CACHE_ADD);
    iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      count++;
    }
    ASSERT_EQ(count, 0);
    ASSERT_TRUE(iter->status().IsIncomplete());
    ASSERT_EQ(numopen, TestGetTickerCount(options, NO_FILE_OPENS));
    ASSERT_EQ(cache_added, TestGetTickerCount(options, BLOCK_CACHE_ADD));
    delete iter;

    // read in the specified block via a regular get
    ASSERT_EQ(Get(1, "a"), "b");

    // verify that we can find it via a non-blocking scan
    numopen = TestGetTickerCount(options, NO_FILE_OPENS);
    cache_added = TestGetTickerCount(options, BLOCK_CACHE_ADD);
    iter = db_->NewIterator(non_blocking_opts, handles_[1]);
    count = 0;
    for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
      ASSERT_OK(iter->status());
      count++;
    }
    ASSERT_EQ(count, 1);
    ASSERT_EQ(numopen, TestGetTickerCount(options, NO_FILE_OPENS));
    ASSERT_EQ(cache_added, TestGetTickerCount(options, BLOCK_CACHE_ADD));
    delete iter;

    // This test verifies block cache behaviors, which is not used by plain
    // table format.
    // Exclude kHashCuckoo as it does not support iteration currently
  } while (ChangeOptions(kSkipPlainTable | kSkipNoSeekToLast | kSkipHashCuckoo |
                         kSkipMmapReads));
}
#endif  // ROCKSDB_LITE

TEST_F(DBIteratorTest, IterSeekBeforePrev) {
  ASSERT_OK(Put("a", "b"));
  ASSERT_OK(Put("c", "d"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put("0", "f"));
  ASSERT_OK(Put("1", "h"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put("2", "j"));
  auto iter = db_->NewIterator(ReadOptions());
  iter->Seek(Slice("c"));
  iter->Prev();
  iter->Seek(Slice("a"));
  iter->Prev();
  delete iter;
}

namespace {
std::string MakeLongKey(size_t length, char c) {
  return std::string(length, c);
}
}  // namespace

TEST_F(DBIteratorTest, IterLongKeys) {
  ASSERT_OK(Put(MakeLongKey(20, 0), "0"));
  ASSERT_OK(Put(MakeLongKey(32, 2), "2"));
  ASSERT_OK(Put("a", "b"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put(MakeLongKey(50, 1), "1"));
  ASSERT_OK(Put(MakeLongKey(127, 3), "3"));
  ASSERT_OK(Put(MakeLongKey(64, 4), "4"));
  auto iter = db_->NewIterator(ReadOptions());

  // Create a key that needs to be skipped for Seq too new
  iter->Seek(MakeLongKey(20, 0));
  ASSERT_EQ(IterStatus(iter), MakeLongKey(20, 0) + "->0");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(50, 1) + "->1");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(32, 2) + "->2");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(127, 3) + "->3");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(64, 4) + "->4");
  delete iter;

  iter = db_->NewIterator(ReadOptions());
  iter->Seek(MakeLongKey(50, 1));
  ASSERT_EQ(IterStatus(iter), MakeLongKey(50, 1) + "->1");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(32, 2) + "->2");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), MakeLongKey(127, 3) + "->3");
  delete iter;
}

TEST_F(DBIteratorTest, IterNextWithNewerSeq) {
  ASSERT_OK(Put("0", "0"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put("a", "b"));
  ASSERT_OK(Put("c", "d"));
  ASSERT_OK(Put("d", "e"));
  auto iter = db_->NewIterator(ReadOptions());

  // Create a key that needs to be skipped for Seq too new
  for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
       i++) {
    ASSERT_OK(Put("b", "f"));
  }

  iter->Seek(Slice("a"));
  ASSERT_EQ(IterStatus(iter), "a->b");
  iter->Next();
  ASSERT_EQ(IterStatus(iter), "c->d");
  delete iter;
}

TEST_F(DBIteratorTest, IterPrevWithNewerSeq) {
  ASSERT_OK(Put("0", "0"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put("a", "b"));
  ASSERT_OK(Put("c", "d"));
  ASSERT_OK(Put("d", "e"));
  auto iter = db_->NewIterator(ReadOptions());

  // Create a key that needs to be skipped for Seq too new
  for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
       i++) {
    ASSERT_OK(Put("b", "f"));
  }

  iter->Seek(Slice("d"));
  ASSERT_EQ(IterStatus(iter), "d->e");
  iter->Prev();
  ASSERT_EQ(IterStatus(iter), "c->d");
  iter->Prev();
  ASSERT_EQ(IterStatus(iter), "a->b");

  iter->Prev();
  delete iter;
}

TEST_F(DBIteratorTest, IterPrevWithNewerSeq2) {
  ASSERT_OK(Put("0", "0"));
  dbfull()->Flush(FlushOptions());
  ASSERT_OK(Put("a", "b"));
  ASSERT_OK(Put("c", "d"));
  ASSERT_OK(Put("d", "e"));
  auto iter = db_->NewIterator(ReadOptions());
  iter->Seek(Slice("c"));
  ASSERT_EQ(IterStatus(iter), "c->d");

  // Create a key that needs to be skipped for Seq too new
  for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
       i++) {
    ASSERT_OK(Put("b", "f"));
  }

  iter->Prev();
  ASSERT_EQ(IterStatus(iter), "a->b");

  iter->Prev();
  delete iter;
}

TEST_F(DBIteratorTest, IterEmpty) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);

    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->Seek("foo");
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    delete iter;
  } while (ChangeCompactOptions());
}

TEST_F(DBIteratorTest, IterSingle) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    ASSERT_OK(Put(1, "a", "va"));
    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);

    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");
    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");
    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->Seek("");
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->Seek("a");
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->Seek("b");
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    delete iter;
  } while (ChangeCompactOptions());
}

TEST_F(DBIteratorTest, IterMulti) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    ASSERT_OK(Put(1, "a", "va"));
    ASSERT_OK(Put(1, "b", "vb"));
    ASSERT_OK(Put(1, "c", "vc"));
    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);

    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "b->vb");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");
    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "b->vb");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");
    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->Seek("");
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Seek("a");
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Seek("ax");
    ASSERT_EQ(IterStatus(iter), "b->vb");

    iter->Seek("b");
    ASSERT_EQ(IterStatus(iter), "b->vb");
    iter->Seek("z");
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    // Switch from reverse to forward
    iter->SeekToLast();
    iter->Prev();
    iter->Prev();
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "b->vb");

    // Switch from forward to reverse
    iter->SeekToFirst();
    iter->Next();
    iter->Next();
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "b->vb");

    // Make sure iter stays at snapshot
    ASSERT_OK(Put(1, "a", "va2"));
    ASSERT_OK(Put(1, "a2", "va3"));
    ASSERT_OK(Put(1, "b", "vb2"));
    ASSERT_OK(Put(1, "c", "vc2"));
    ASSERT_OK(Delete(1, "b"));
    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "b->vb");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");
    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "b->vb");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    delete iter;
  } while (ChangeCompactOptions());
}

// Check that we can skip over a run of user keys
// by using reseek rather than sequential scan
TEST_F(DBIteratorTest, IterReseek) {
  anon::OptionsOverride options_override;
  options_override.skip_policy = kSkipNoSnapshot;
  Options options = CurrentOptions(options_override);
  options.max_sequential_skip_in_iterations = 3;
  options.create_if_missing = true;
  options.statistics = rocksdb::CreateDBStatistics();
  DestroyAndReopen(options);
  CreateAndReopenWithCF({"pikachu"}, options);

  // insert three keys with same userkey and verify that
  // reseek is not invoked. For each of these test cases,
  // verify that we can find the next key "b".
  ASSERT_OK(Put(1, "a", "zero"));
  ASSERT_OK(Put(1, "a", "one"));
  ASSERT_OK(Put(1, "a", "two"));
  ASSERT_OK(Put(1, "b", "bone"));
  Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);
  iter->SeekToFirst();
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 0);
  ASSERT_EQ(IterStatus(iter), "a->two");
  iter->Next();
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 0);
  ASSERT_EQ(IterStatus(iter), "b->bone");
  delete iter;

  // insert a total of three keys with same userkey and verify
  // that reseek is still not invoked.
  ASSERT_OK(Put(1, "a", "three"));
  iter = db_->NewIterator(ReadOptions(), handles_[1]);
  iter->SeekToFirst();
  ASSERT_EQ(IterStatus(iter), "a->three");
  iter->Next();
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 0);
  ASSERT_EQ(IterStatus(iter), "b->bone");
  delete iter;

  // insert a total of four keys with same userkey and verify
  // that reseek is invoked.
  ASSERT_OK(Put(1, "a", "four"));
  iter = db_->NewIterator(ReadOptions(), handles_[1]);
  iter->SeekToFirst();
  ASSERT_EQ(IterStatus(iter), "a->four");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 0);
  iter->Next();
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION), 1);
  ASSERT_EQ(IterStatus(iter), "b->bone");
  delete iter;

  // Testing reverse iterator
  // At this point, we have three versions of "a" and one version of "b".
  // The reseek statistics is already at 1.
  int num_reseeks = static_cast<int>(
      TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION));

  // Insert another version of b and assert that reseek is not invoked
  ASSERT_OK(Put(1, "b", "btwo"));
  iter = db_->NewIterator(ReadOptions(), handles_[1]);
  iter->SeekToLast();
  ASSERT_EQ(IterStatus(iter), "b->btwo");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION),
            num_reseeks);
  iter->Prev();
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION),
            num_reseeks + 1);
  ASSERT_EQ(IterStatus(iter), "a->four");
  delete iter;

  // insert two more versions of b. This makes a total of 4 versions
  // of b and 4 versions of a.
  ASSERT_OK(Put(1, "b", "bthree"));
  ASSERT_OK(Put(1, "b", "bfour"));
  iter = db_->NewIterator(ReadOptions(), handles_[1]);
  iter->SeekToLast();
  ASSERT_EQ(IterStatus(iter), "b->bfour");
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION),
            num_reseeks + 2);
  iter->Prev();

  // the previous Prev call should have invoked reseek
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_OF_RESEEKS_IN_ITERATION),
            num_reseeks + 3);
  ASSERT_EQ(IterStatus(iter), "a->four");
  delete iter;
}

TEST_F(DBIteratorTest, IterSmallAndLargeMix) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    ASSERT_OK(Put(1, "a", "va"));
    ASSERT_OK(Put(1, "b", std::string(100000, 'b')));
    ASSERT_OK(Put(1, "c", "vc"));
    ASSERT_OK(Put(1, "d", std::string(100000, 'd')));
    ASSERT_OK(Put(1, "e", std::string(100000, 'e')));

    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);

    iter->SeekToFirst();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "b->" + std::string(100000, 'b'));
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "d->" + std::string(100000, 'd'));
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "e->" + std::string(100000, 'e'));
    iter->Next();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    iter->SeekToLast();
    ASSERT_EQ(IterStatus(iter), "e->" + std::string(100000, 'e'));
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "d->" + std::string(100000, 'd'));
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "c->vc");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "b->" + std::string(100000, 'b'));
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "a->va");
    iter->Prev();
    ASSERT_EQ(IterStatus(iter), "(invalid)");

    delete iter;
  } while (ChangeCompactOptions());
}

TEST_F(DBIteratorTest, IterMultiWithDelete) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    ASSERT_OK(Put(1, "ka", "va"));
    ASSERT_OK(Put(1, "kb", "vb"));
    ASSERT_OK(Put(1, "kc", "vc"));
    ASSERT_OK(Delete(1, "kb"));
    ASSERT_EQ("NOT_FOUND", Get(1, "kb"));

    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);
    iter->Seek("kc");
    ASSERT_EQ(IterStatus(iter), "kc->vc");
    if (!CurrentOptions().merge_operator) {
      // TODO: merge operator does not support backward iteration yet
      if (kPlainTableAllBytesPrefix != option_config_ &&
          kBlockBasedTableWithWholeKeyHashIndex != option_config_ &&
          kHashLinkList != option_config_) {
        iter->Prev();
        ASSERT_EQ(IterStatus(iter), "ka->va");
      }
    }
    delete iter;
  } while (ChangeOptions());
}

TEST_F(DBIteratorTest, IterPrevMaxSkip) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    for (int i = 0; i < 2; i++) {
      ASSERT_OK(Put(1, "key1", "v1"));
      ASSERT_OK(Put(1, "key2", "v2"));
      ASSERT_OK(Put(1, "key3", "v3"));
      ASSERT_OK(Put(1, "key4", "v4"));
      ASSERT_OK(Put(1, "key5", "v5"));
    }

    VerifyIterLast("key5->v5", 1);

    ASSERT_OK(Delete(1, "key5"));
    VerifyIterLast("key4->v4", 1);

    ASSERT_OK(Delete(1, "key4"));
    VerifyIterLast("key3->v3", 1);

    ASSERT_OK(Delete(1, "key3"));
    VerifyIterLast("key2->v2", 1);

    ASSERT_OK(Delete(1, "key2"));
    VerifyIterLast("key1->v1", 1);

    ASSERT_OK(Delete(1, "key1"));
    VerifyIterLast("(invalid)", 1);
  } while (ChangeOptions(kSkipMergePut | kSkipNoSeekToLast));
}

TEST_F(DBIteratorTest, IterWithSnapshot) {
  anon::OptionsOverride options_override;
  options_override.skip_policy = kSkipNoSnapshot;
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions(options_override));
    ASSERT_OK(Put(1, "key1", "val1"));
    ASSERT_OK(Put(1, "key2", "val2"));
    ASSERT_OK(Put(1, "key3", "val3"));
    ASSERT_OK(Put(1, "key4", "val4"));
    ASSERT_OK(Put(1, "key5", "val5"));

    const Snapshot* snapshot = db_->GetSnapshot();
    ReadOptions options;
    options.snapshot = snapshot;
    Iterator* iter = db_->NewIterator(options, handles_[1]);

    // Put more values after the snapshot
    ASSERT_OK(Put(1, "key100", "val100"));
    ASSERT_OK(Put(1, "key101", "val101"));

    iter->Seek("key5");
    ASSERT_EQ(IterStatus(iter), "key5->val5");
    if (!CurrentOptions().merge_operator) {
      // TODO: merge operator does not support backward iteration yet
      if (kPlainTableAllBytesPrefix != option_config_ &&
          kBlockBasedTableWithWholeKeyHashIndex != option_config_ &&
          kHashLinkList != option_config_) {
        iter->Prev();
        ASSERT_EQ(IterStatus(iter), "key4->val4");
        iter->Prev();
        ASSERT_EQ(IterStatus(iter), "key3->val3");

        iter->Next();
        ASSERT_EQ(IterStatus(iter), "key4->val4");
        iter->Next();
        ASSERT_EQ(IterStatus(iter), "key5->val5");
      }
      iter->Next();
      ASSERT_TRUE(!iter->Valid());
    }
    db_->ReleaseSnapshot(snapshot);
    delete iter;
    // skip as HashCuckooRep does not support snapshot
  } while (ChangeOptions(kSkipHashCuckoo));
}

TEST_F(DBIteratorTest, IteratorPinsRef) {
  do {
    CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
    Put(1, "foo", "hello");

    // Get iterator that will yield the current contents of the DB.
    Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);

    // Write to force compactions
    Put(1, "foo", "newvalue1");
    for (int i = 0; i < 100; i++) {
      // 100K values
      ASSERT_OK(Put(1, Key(i), Key(i) + std::string(100000, 'v')));
    }
    Put(1, "foo", "newvalue2");

    iter->SeekToFirst();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ("foo", iter->key().ToString());
    ASSERT_EQ("hello", iter->value().ToString());
    iter->Next();
    ASSERT_TRUE(!iter->Valid());
    delete iter;
  } while (ChangeCompactOptions());
}

TEST_F(DBIteratorTest, DBIteratorBoundTest) {
  Options options = CurrentOptions();
  options.env = env_;
  options.create_if_missing = true;

  options.prefix_extractor = nullptr;
  DestroyAndReopen(options);
  ASSERT_OK(Put("a", "0"));
  ASSERT_OK(Put("foo", "bar"));
  ASSERT_OK(Put("foo1", "bar1"));
  ASSERT_OK(Put("g1", "0"));

  // testing basic case with no iterate_upper_bound and no prefix_extractor
  {
    ReadOptions ro;
    ro.iterate_upper_bound = nullptr;

    std::unique_ptr<Iterator> iter(db_->NewIterator(ro));

    iter->Seek("foo");

    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("foo")), 0);

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("foo1")), 0);

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("g1")), 0);
  }

  // testing iterate_upper_bound and forward iterator
  // to make sure it stops at bound
  {
    ReadOptions ro;
    // iterate_upper_bound points beyond the last expected entry
    Slice prefix("foo2");
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> iter(db_->NewIterator(ro));

    iter->Seek("foo");

    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("foo")), 0);

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(("foo1")), 0);

    iter->Next();
    // should stop here...
    ASSERT_TRUE(!iter->Valid());
  }
  // Testing SeekToLast with iterate_upper_bound set
  {
    ReadOptions ro;

    Slice prefix("foo");
    ro.iterate_upper_bound = &prefix;

    std::unique_ptr<Iterator> iter(db_->NewIterator(ro));

    iter->SeekToLast();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("a")), 0);
  }

  // prefix is the first letter of the key
  options.prefix_extractor.reset(NewFixedPrefixTransform(1));

  DestroyAndReopen(options);
  ASSERT_OK(Put("a", "0"));
  ASSERT_OK(Put("foo", "bar"));
  ASSERT_OK(Put("foo1", "bar1"));
  ASSERT_OK(Put("g1", "0"));

  // testing with iterate_upper_bound and prefix_extractor
  // Seek target and iterate_upper_bound are not is same prefix
  // This should be an error
  {
    ReadOptions ro;
    Slice upper_bound("g");
    ro.iterate_upper_bound = &upper_bound;

    std::unique_ptr<Iterator> iter(db_->NewIterator(ro));

    iter->Seek("foo");

    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ("foo", iter->key().ToString());

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ("foo1", iter->key().ToString());

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

  // testing that iterate_upper_bound prevents iterating over deleted items
  // if the bound has already reached
  {
    options.prefix_extractor = nullptr;
    DestroyAndReopen(options);
    ASSERT_OK(Put("a", "0"));
    ASSERT_OK(Put("b", "0"));
    ASSERT_OK(Put("b1", "0"));
    ASSERT_OK(Put("c", "0"));
    ASSERT_OK(Put("d", "0"));
    ASSERT_OK(Put("e", "0"));
    ASSERT_OK(Delete("c"));
    ASSERT_OK(Delete("d"));

    // base case with no bound
    ReadOptions ro;
    ro.iterate_upper_bound = nullptr;

    std::unique_ptr<Iterator> iter(db_->NewIterator(ro));

    iter->Seek("b");
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("b")), 0);

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(("b1")), 0);

    perf_context.Reset();
    iter->Next();

    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(static_cast<int>(perf_context.internal_delete_skipped_count), 2);

    // now testing with iterate_bound
    Slice prefix("c");
    ro.iterate_upper_bound = &prefix;

    iter.reset(db_->NewIterator(ro));

    perf_context.Reset();

    iter->Seek("b");
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(Slice("b")), 0);

    iter->Next();
    ASSERT_TRUE(iter->Valid());
    ASSERT_EQ(iter->key().compare(("b1")), 0);

    iter->Next();
    // the iteration should stop as soon as the bound key is reached
    // even though the key is deleted
    // hence internal_delete_skipped_count should be 0
    ASSERT_TRUE(!iter->Valid());
    ASSERT_EQ(static_cast<int>(perf_context.internal_delete_skipped_count), 0);
  }
}

// TODO(3.13): fix the issue of Seek() + Prev() which might not necessary
//             return the biggest key which is smaller than the seek key.
TEST_F(DBIteratorTest, PrevAfterMerge) {
  Options options;
  options.create_if_missing = true;
  options.merge_operator = MergeOperators::CreatePutOperator();
  DestroyAndReopen(options);

  // write three entries with different keys using Merge()
  WriteOptions wopts;
  db_->Merge(wopts, "1", "data1");
  db_->Merge(wopts, "2", "data2");
  db_->Merge(wopts, "3", "data3");

  std::unique_ptr<Iterator> it(db_->NewIterator(ReadOptions()));

  it->Seek("2");
  ASSERT_TRUE(it->Valid());
  ASSERT_EQ("2", it->key().ToString());

  it->Prev();
  ASSERT_TRUE(it->Valid());
  ASSERT_EQ("1", it->key().ToString());
}

TEST_F(DBIteratorTest, PinnedDataIteratorRandomized) {
  enum TestConfig {
    NORMAL,
    CLOSE_AND_OPEN,
    COMPACT_BEFORE_READ,
    FLUSH_EVERY_1000,
    MAX
  };

  // Generate Random data
  Random rnd(301);

  int puts = 100000;
  int key_pool = static_cast<int>(puts * 0.7);
  int key_size = 100;
  int val_size = 1000;
  int seeks_percentage = 20;   // 20% of keys will be used to test seek()
  int delete_percentage = 20;  // 20% of keys will be deleted
  int merge_percentage = 20;   // 20% of keys will be added using Merge()

  for (int run_config = 0; run_config < TestConfig::MAX; run_config++) {
    Options options = CurrentOptions();
    BlockBasedTableOptions table_options;
    table_options.use_delta_encoding = false;
    options.table_factory.reset(NewBlockBasedTableFactory(table_options));
    options.merge_operator = MergeOperators::CreatePutOperator();
    DestroyAndReopen(options);

    std::vector<std::string> generated_keys(key_pool);
    for (int i = 0; i < key_pool; i++) {
      generated_keys[i] = RandomString(&rnd, key_size);
    }

    std::map<std::string, std::string> true_data;
    std::vector<std::string> random_keys;
    std::vector<std::string> deleted_keys;
    for (int i = 0; i < puts; i++) {
      auto& k = generated_keys[rnd.Next() % key_pool];
      auto v = RandomString(&rnd, val_size);

      // Insert data to true_data map and to DB
      true_data[k] = v;
      if (rnd.OneIn(static_cast<int>(100.0 / merge_percentage))) {
        ASSERT_OK(db_->Merge(WriteOptions(), k, v));
      } else {
        ASSERT_OK(Put(k, v));
      }

      // Pick random keys to be used to test Seek()
      if (rnd.OneIn(static_cast<int>(100.0 / seeks_percentage))) {
        random_keys.push_back(k);
      }

      // Delete some random keys
      if (rnd.OneIn(static_cast<int>(100.0 / delete_percentage))) {
        deleted_keys.push_back(k);
        true_data.erase(k);
        ASSERT_OK(Delete(k));
      }

      if (run_config == TestConfig::FLUSH_EVERY_1000) {
        if (i && i % 1000 == 0) {
          Flush();
        }
      }
    }

    if (run_config == TestConfig::CLOSE_AND_OPEN) {
      Close();
      Reopen(options);
    } else if (run_config == TestConfig::COMPACT_BEFORE_READ) {
      db_->CompactRange(CompactRangeOptions(), nullptr, nullptr);
    }

    ReadOptions ro;
    ro.pin_data = true;
    auto iter = db_->NewIterator(ro);

    {
      // Test Seek to random keys
      printf("Testing seek on %zu keys\n", random_keys.size());
      std::vector<Slice> keys_slices;
      std::vector<std::string> true_keys;
      for (auto& k : random_keys) {
        iter->Seek(k);
        if (!iter->Valid()) {
          ASSERT_EQ(true_data.lower_bound(k), true_data.end());
          continue;
        }
        std::string prop_value;
        ASSERT_OK(
            iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
        ASSERT_EQ("1", prop_value);
        keys_slices.push_back(iter->key());
        true_keys.push_back(true_data.lower_bound(k)->first);
      }

      for (size_t i = 0; i < keys_slices.size(); i++) {
        ASSERT_EQ(keys_slices[i].ToString(), true_keys[i]);
      }
    }

    {
      // Test iterating all data forward
      printf("Testing iterating forward on all keys\n");
      std::vector<Slice> all_keys;
      for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
        std::string prop_value;
        ASSERT_OK(
            iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
        ASSERT_EQ("1", prop_value);
        all_keys.push_back(iter->key());
      }
      ASSERT_EQ(all_keys.size(), true_data.size());

      // Verify that all keys slices are valid
      auto data_iter = true_data.begin();
      for (size_t i = 0; i < all_keys.size(); i++) {
        ASSERT_EQ(all_keys[i].ToString(), data_iter->first);
        data_iter++;
      }
    }

    {
      // Test iterating all data backward
      printf("Testing iterating backward on all keys\n");
      std::vector<Slice> all_keys;
      for (iter->SeekToLast(); iter->Valid(); iter->Prev()) {
        std::string prop_value;
        ASSERT_OK(
            iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
        ASSERT_EQ("1", prop_value);
        all_keys.push_back(iter->key());
      }
      ASSERT_EQ(all_keys.size(), true_data.size());

      // Verify that all keys slices are valid (backward)
      auto data_iter = true_data.rbegin();
      for (size_t i = 0; i < all_keys.size(); i++) {
        ASSERT_EQ(all_keys[i].ToString(), data_iter->first);
        data_iter++;
      }
    }

    delete iter;
  }
}

#ifndef ROCKSDB_LITE
TEST_F(DBIteratorTest, PinnedDataIteratorMultipleFiles) {
  Options options = CurrentOptions();
  BlockBasedTableOptions table_options;
  table_options.use_delta_encoding = false;
  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
  options.disable_auto_compactions = true;
  options.write_buffer_size = 1024 * 1024 * 10;  // 10 Mb
  DestroyAndReopen(options);

  std::map<std::string, std::string> true_data;

  // Generate 4 sst files in L2
  Random rnd(301);
  for (int i = 1; i <= 1000; i++) {
    std::string k = Key(i * 3);
    std::string v = RandomString(&rnd, 100);
    ASSERT_OK(Put(k, v));
    true_data[k] = v;
    if (i % 250 == 0) {
      ASSERT_OK(Flush());
    }
  }
  ASSERT_EQ(FilesPerLevel(0), "4");
  ASSERT_OK(db_->CompactRange(CompactRangeOptions(), nullptr, nullptr));
  ASSERT_EQ(FilesPerLevel(0), "0,4");

  // Generate 4 sst files in L0
  for (int i = 1; i <= 1000; i++) {
    std::string k = Key(i * 2);
    std::string v = RandomString(&rnd, 100);
    ASSERT_OK(Put(k, v));
    true_data[k] = v;
    if (i % 250 == 0) {
      ASSERT_OK(Flush());
    }
  }
  ASSERT_EQ(FilesPerLevel(0), "4,4");

  // Add some keys/values in memtables
  for (int i = 1; i <= 1000; i++) {
    std::string k = Key(i);
    std::string v = RandomString(&rnd, 100);
    ASSERT_OK(Put(k, v));
    true_data[k] = v;
  }
  ASSERT_EQ(FilesPerLevel(0), "4,4");

  ReadOptions ro;
  ro.pin_data = true;
  auto iter = db_->NewIterator(ro);

  std::vector<std::pair<Slice, std::string>> results;
  for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
    std::string prop_value;
    ASSERT_OK(iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
    ASSERT_EQ("1", prop_value);
    results.emplace_back(iter->key(), iter->value().ToString());
  }

  ASSERT_EQ(results.size(), true_data.size());
  auto data_iter = true_data.begin();
  for (size_t i = 0; i < results.size(); i++, data_iter++) {
    auto& kv = results[i];
    ASSERT_EQ(kv.first, data_iter->first);
    ASSERT_EQ(kv.second, data_iter->second);
  }

  delete iter;
}
#endif

TEST_F(DBIteratorTest, PinnedDataIteratorMergeOperator) {
  Options options = CurrentOptions();
  BlockBasedTableOptions table_options;
  table_options.use_delta_encoding = false;
  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
  options.merge_operator = MergeOperators::CreateUInt64AddOperator();
  DestroyAndReopen(options);

  std::string numbers[7];
  for (int val = 0; val <= 6; val++) {
    PutFixed64(numbers + val, val);
  }

  // +1 all keys in range [ 0 => 999]
  for (int i = 0; i < 1000; i++) {
    WriteOptions wo;
    ASSERT_OK(db_->Merge(wo, Key(i), numbers[1]));
  }

  // +2 all keys divisible by 2 in range [ 0 => 999]
  for (int i = 0; i < 1000; i += 2) {
    WriteOptions wo;
    ASSERT_OK(db_->Merge(wo, Key(i), numbers[2]));
  }

  // +3 all keys divisible by 5 in range [ 0 => 999]
  for (int i = 0; i < 1000; i += 5) {
    WriteOptions wo;
    ASSERT_OK(db_->Merge(wo, Key(i), numbers[3]));
  }

  ReadOptions ro;
  ro.pin_data = true;
  auto iter = db_->NewIterator(ro);

  std::vector<std::pair<Slice, std::string>> results;
  for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
    std::string prop_value;
    ASSERT_OK(iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
    ASSERT_EQ("1", prop_value);
    results.emplace_back(iter->key(), iter->value().ToString());
  }

  ASSERT_EQ(results.size(), 1000);
  for (size_t i = 0; i < results.size(); i++) {
    auto& kv = results[i];
    ASSERT_EQ(kv.first, Key(static_cast<int>(i)));
    int expected_val = 1;
    if (i % 2 == 0) {
      expected_val += 2;
    }
    if (i % 5 == 0) {
      expected_val += 3;
    }
    ASSERT_EQ(kv.second, numbers[expected_val]);
  }

  delete iter;
}

TEST_F(DBIteratorTest, PinnedDataIteratorReadAfterUpdate) {
  Options options = CurrentOptions();
  BlockBasedTableOptions table_options;
  table_options.use_delta_encoding = false;
  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
  options.write_buffer_size = 100000;
  DestroyAndReopen(options);

  Random rnd(301);

  std::map<std::string, std::string> true_data;
  for (int i = 0; i < 1000; i++) {
    std::string k = RandomString(&rnd, 10);
    std::string v = RandomString(&rnd, 1000);
    ASSERT_OK(Put(k, v));
    true_data[k] = v;
  }

  ReadOptions ro;
  ro.pin_data = true;
  auto iter = db_->NewIterator(ro);

  // Delete 50% of the keys and update the other 50%
  for (auto& kv : true_data) {
    if (rnd.OneIn(2)) {
      ASSERT_OK(Delete(kv.first));
    } else {
      std::string new_val = RandomString(&rnd, 1000);
      ASSERT_OK(Put(kv.first, new_val));
    }
  }

  std::vector<std::pair<Slice, std::string>> results;
  for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
    std::string prop_value;
    ASSERT_OK(iter->GetProperty("rocksdb.iterator.is-key-pinned", &prop_value));
    ASSERT_EQ("1", prop_value);
    results.emplace_back(iter->key(), iter->value().ToString());
  }

  auto data_iter = true_data.begin();
  for (size_t i = 0; i < results.size(); i++, data_iter++) {
    auto& kv = results[i];
    ASSERT_EQ(kv.first, data_iter->first);
    ASSERT_EQ(kv.second, data_iter->second);
  }

  delete iter;
}

TEST_F(DBIteratorTest, IterPrevKeyCrossingBlocks) {
  Options options = CurrentOptions();
  BlockBasedTableOptions table_options;
  table_options.block_size = 1;  // every block will contain one entry
  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
  options.merge_operator = MergeOperators::CreateStringAppendTESTOperator();
  options.disable_auto_compactions = true;
  options.max_sequential_skip_in_iterations = 8;

  DestroyAndReopen(options);

  // Putting such deletes will force DBIter::Prev() to fallback to a Seek
  for (int file_num = 0; file_num < 10; file_num++) {
    ASSERT_OK(Delete("key4"));
    ASSERT_OK(Flush());
  }

  // First File containing 5 blocks of puts
  ASSERT_OK(Put("key1", "val1.0"));
  ASSERT_OK(Put("key2", "val2.0"));
  ASSERT_OK(Put("key3", "val3.0"));
  ASSERT_OK(Put("key4", "val4.0"));
  ASSERT_OK(Put("key5", "val5.0"));
  ASSERT_OK(Flush());

  // Second file containing 9 blocks of merge operands
  ASSERT_OK(db_->Merge(WriteOptions(), "key1", "val1.1"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key1", "val1.2"));

  ASSERT_OK(db_->Merge(WriteOptions(), "key2", "val2.1"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key2", "val2.2"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key2", "val2.3"));

  ASSERT_OK(db_->Merge(WriteOptions(), "key3", "val3.1"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key3", "val3.2"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key3", "val3.3"));
  ASSERT_OK(db_->Merge(WriteOptions(), "key3", "val3.4"));
  ASSERT_OK(Flush());

  {
    ReadOptions ro;
    ro.fill_cache = false;
    Iterator* iter = db_->NewIterator(ro);

    iter->SeekToLast();
    ASSERT_EQ(iter->key().ToString(), "key5");
    ASSERT_EQ(iter->value().ToString(), "val5.0");

    iter->Prev();
    ASSERT_EQ(iter->key().ToString(), "key4");
    ASSERT_EQ(iter->value().ToString(), "val4.0");

    iter->Prev();
    ASSERT_EQ(iter->key().ToString(), "key3");
    ASSERT_EQ(iter->value().ToString(), "val3.0,val3.1,val3.2,val3.3,val3.4");

    iter->Prev();
    ASSERT_EQ(iter->key().ToString(), "key2");
    ASSERT_EQ(iter->value().ToString(), "val2.0,val2.1,val2.2,val2.3");

    iter->Prev();
    ASSERT_EQ(iter->key().ToString(), "key1");
    ASSERT_EQ(iter->value().ToString(), "val1.0,val1.1,val1.2");

    delete iter;
  }
}

TEST_F(DBIteratorTest, IterPrevKeyCrossingBlocksRandomized) {
  Options options = CurrentOptions();
  options.merge_operator = MergeOperators::CreateStringAppendTESTOperator();
  options.disable_auto_compactions = true;
  options.level0_slowdown_writes_trigger = (1 << 30);
  options.level0_stop_writes_trigger = (1 << 30);
  options.max_sequential_skip_in_iterations = 8;
  DestroyAndReopen(options);

  const int kNumKeys = 500;
  // Small number of merge operands to make sure that DBIter::Prev() dont
  // fall back to Seek()
  const int kNumMergeOperands = 3;
  // Use value size that will make sure that every block contain 1 key
  const int kValSize =
      static_cast<int>(BlockBasedTableOptions().block_size) * 4;
  // Percentage of keys that wont get merge operations
  const int kNoMergeOpPercentage = 20;
  // Percentage of keys that will be deleted
  const int kDeletePercentage = 10;

  // For half of the key range we will write multiple deletes first to
  // force DBIter::Prev() to fall back to Seek()
  for (int file_num = 0; file_num < 10; file_num++) {
    for (int i = 0; i < kNumKeys; i += 2) {
      ASSERT_OK(Delete(Key(i)));
    }
    ASSERT_OK(Flush());
  }

  Random rnd(301);
  std::map<std::string, std::string> true_data;
  std::string gen_key;
  std::string gen_val;

  for (int i = 0; i < kNumKeys; i++) {
    gen_key = Key(i);
    gen_val = RandomString(&rnd, kValSize);

    ASSERT_OK(Put(gen_key, gen_val));
    true_data[gen_key] = gen_val;
  }
  ASSERT_OK(Flush());

  // Separate values and merge operands in different file so that we
  // make sure that we dont merge them while flushing but actually
  // merge them in the read path
  for (int i = 0; i < kNumKeys; i++) {
    if (rnd.OneIn(static_cast<int>(100.0 / kNoMergeOpPercentage))) {
      // Dont give merge operations for some keys
      continue;
    }

    for (int j = 0; j < kNumMergeOperands; j++) {
      gen_key = Key(i);
      gen_val = RandomString(&rnd, kValSize);

      ASSERT_OK(db_->Merge(WriteOptions(), gen_key, gen_val));
      true_data[gen_key] += "," + gen_val;
    }
  }
  ASSERT_OK(Flush());

  for (int i = 0; i < kNumKeys; i++) {
    if (rnd.OneIn(static_cast<int>(100.0 / kDeletePercentage))) {
      gen_key = Key(i);

      ASSERT_OK(Delete(gen_key));
      true_data.erase(gen_key);
    }
  }
  ASSERT_OK(Flush());

  {
    ReadOptions ro;
    ro.fill_cache = false;
    Iterator* iter = db_->NewIterator(ro);
    auto data_iter = true_data.rbegin();

    for (iter->SeekToLast(); iter->Valid(); iter->Prev()) {
      ASSERT_EQ(iter->key().ToString(), data_iter->first);
      ASSERT_EQ(iter->value().ToString(), data_iter->second);
      data_iter++;
    }
    ASSERT_EQ(data_iter, true_data.rend());

    delete iter;
  }
}

TEST_F(DBIteratorTest, IteratorWithLocalStatistics) {
  Options options = CurrentOptions();
  options.statistics = rocksdb::CreateDBStatistics();
  DestroyAndReopen(options);

  Random rnd(301);
  for (int i = 0; i < 1000; i++) {
    // Key 10 bytes / Value 10 bytes
    ASSERT_OK(Put(RandomString(&rnd, 10), RandomString(&rnd, 10)));
  }

  std::atomic<uint64_t> total_next(0);
  std::atomic<uint64_t> total_next_found(0);
  std::atomic<uint64_t> total_prev(0);
  std::atomic<uint64_t> total_prev_found(0);
  std::atomic<uint64_t> total_bytes(0);

  std::vector<std::thread> threads;
  std::function<void()> reader_func_next = [&]() {
    Iterator* iter = db_->NewIterator(ReadOptions());

    iter->SeekToFirst();
    // Seek will bump ITER_BYTES_READ
    total_bytes += iter->key().size();
    total_bytes += iter->value().size();
    while (true) {
      iter->Next();
      total_next++;

      if (!iter->Valid()) {
        break;
      }
      total_next_found++;
      total_bytes += iter->key().size();
      total_bytes += iter->value().size();
    }

    delete iter;
  };

  std::function<void()> reader_func_prev = [&]() {
    Iterator* iter = db_->NewIterator(ReadOptions());

    iter->SeekToLast();
    // Seek will bump ITER_BYTES_READ
    total_bytes += iter->key().size();
    total_bytes += iter->value().size();
    while (true) {
      iter->Prev();
      total_prev++;

      if (!iter->Valid()) {
        break;
      }
      total_prev_found++;
      total_bytes += iter->key().size();
      total_bytes += iter->value().size();
    }

    delete iter;
  };

  for (int i = 0; i < 10; i++) {
    threads.emplace_back(reader_func_next);
  }
  for (int i = 0; i < 15; i++) {
    threads.emplace_back(reader_func_prev);
  }

  for (auto& t : threads) {
    t.join();
  }

  ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_NEXT), total_next);
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_NEXT_FOUND),
            total_next_found);
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_PREV), total_prev);
  ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_PREV_FOUND),
            total_prev_found);
  ASSERT_EQ(TestGetTickerCount(options, ITER_BYTES_READ), total_bytes);
}

}  // namespace rocksdb

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