rocksdb/table/block_based_table_factory.cc

//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "table/block_based_table_factory.h"

#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif

#include <inttypes.h>
#include <stdint.h>

#include <memory>
#include <string>

#include "options/options_helper.h"
#include "port/port.h"
#include "rocksdb/cache.h"
#include "rocksdb/convenience.h"
#include "rocksdb/flush_block_policy.h"
#include "table/block_based_table_builder.h"
#include "table/block_based_table_reader.h"
#include "table/format.h"
#include "util/mutexlock.h"
#include "util/string_util.h"

namespace rocksdb {

void TailPrefetchStats::RecordEffectiveSize(size_t len) {
  MutexLock l(&mutex_);
  if (num_records_ < kNumTracked) {
    num_records_++;
  }
  records_[next_++] = len;
  if (next_ == kNumTracked) {
    next_ = 0;
  }
}

size_t TailPrefetchStats::GetSuggestedPrefetchSize() {
  std::vector<size_t> sorted;
  {
    MutexLock l(&mutex_);

    if (num_records_ == 0) {
      return 0;
    }
    sorted.assign(records_, records_ + num_records_);
  }

  // Of the historic size, we find the maximum one that satisifis the condtiion
  // that if prefetching all, less than 1/8 will be wasted.
  std::sort(sorted.begin(), sorted.end());

  // Assuming we have 5 data points, and after sorting it looks like this:
  //
  //                                     +---+
  //                             +---+   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                    +---+    |   |   |   |
  //                    |   |    |   |   |   |
  //           +---+    |   |    |   |   |   |
  //           |   |    |   |    |   |   |   |
  //  +---+    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  +---+    +---+    +---+    +---+   +---+
  //
  // and we use every of the value as a candidate, and estimate how much we
  // wasted, compared to read. For example, when we use the 3rd record
  // as candiate. This area is what we read:
  //                                     +---+
  //                             +---+   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //  ***  ***  ***  ***+ ***  ***  *** *** **
  //  *                 |   |    |   |   |   |
  //           +---+    |   |    |   |   |   *
  //  *        |   |    |   |    |   |   |   |
  //  +---+    |   |    |   |    |   |   |   *
  //  *   |    |   |    | X |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   *
  //  *   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   *
  //  *   |    |   |    |   |    |   |   |   |
  //  *** *** ***-***  ***--*** ***--*** +****
  // which is (size of the record) X (number of records).
  //
  // While wasted is this area:
  //                                     +---+
  //                             +---+   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //                             |   |   |   |
  //  ***  ***  ***  ****---+    |   |   |   |
  //  *                 *   |    |   |   |   |
  //  *        *-***  ***   |    |   |   |   |
  //  *        *   |    |   |    |   |   |   |
  //  *--**  ***   |    |   |    |   |   |   |
  //  |   |    |   |    | X |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  +---+    +---+    +---+    +---+   +---+
  //
  // Which can be calculated iteratively.
  // The difference between wasted using 4st and 3rd record, will
  // be following area:
  //                                     +---+
  //  +--+  +-+   ++  +-+  +-+   +---+   |   |
  //  + xxxxxxxxxxxxxxxxxxxxxxxx |   |   |   |
  //    xxxxxxxxxxxxxxxxxxxxxxxx |   |   |   |
  //  + xxxxxxxxxxxxxxxxxxxxxxxx |   |   |   |
  //  | xxxxxxxxxxxxxxxxxxxxxxxx |   |   |   |
  //  +-+ +-+  +-+  ++  +---+ +--+   |   |   |
  //  |                 |   |    |   |   |   |
  //           +---+ ++ |   |    |   |   |   |
  //  |        |   |    |   |    | X |   |   |
  //  +---+ ++ |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  |   |    |   |    |   |    |   |   |   |
  //  +---+    +---+    +---+    +---+   +---+
  //
  // which will be the size difference between 4st and 3rd record,
  // times 3, which is number of records before the 4st.
  // Here we assume that all data within the prefetch range will be useful. In
  // reality, it may not be the case when a partial block is inside the range,
  // or there are data in the middle that is not read. We ignore those cases
  // for simplicity.
  assert(!sorted.empty());
  size_t prev_size = sorted[0];
  size_t max_qualified_size = sorted[0];
  size_t wasted = 0;
  for (size_t i = 1; i < sorted.size(); i++) {
    size_t read = sorted[i] * sorted.size();
    wasted += (sorted[i] - prev_size) * i;
    if (wasted <= read / 8) {
      max_qualified_size = sorted[i];
    }
    prev_size = sorted[i];
  }
  const size_t kMaxPrefetchSize = 512 * 1024;  // Never exceed 512KB
  return std::min(kMaxPrefetchSize, max_qualified_size);
}

BlockBasedTableFactory::BlockBasedTableFactory(
    const BlockBasedTableOptions& _table_options)
    : table_options_(_table_options) {
  if (table_options_.flush_block_policy_factory == nullptr) {
    table_options_.flush_block_policy_factory.reset(
        new FlushBlockBySizePolicyFactory());
  }
  if (table_options_.no_block_cache) {
    table_options_.block_cache.reset();
  } else if (table_options_.block_cache == nullptr) {
    table_options_.block_cache = NewLRUCache(8 << 20);
  }
  if (table_options_.block_size_deviation < 0 ||
      table_options_.block_size_deviation > 100) {
    table_options_.block_size_deviation = 0;
  }
  if (table_options_.block_restart_interval < 1) {
    table_options_.block_restart_interval = 1;
  }
  if (table_options_.index_block_restart_interval < 1) {
    table_options_.index_block_restart_interval = 1;
  }
  if (table_options_.partition_filters &&
      table_options_.index_type !=
          BlockBasedTableOptions::kTwoLevelIndexSearch) {
    // We do not support partitioned filters without partitioning indexes
    table_options_.partition_filters = false;
  }
}

Status BlockBasedTableFactory::NewTableReader(
    const TableReaderOptions& table_reader_options,
    std::unique_ptr<RandomAccessFileReader>&& file, uint64_t file_size,
    std::unique_ptr<TableReader>* table_reader,
    bool prefetch_index_and_filter_in_cache) const {
  return BlockBasedTable::Open(
      table_reader_options.ioptions, table_reader_options.env_options,
      table_options_, table_reader_options.internal_comparator, std::move(file),
      file_size, table_reader, table_reader_options.prefix_extractor,
      prefetch_index_and_filter_in_cache, table_reader_options.skip_filters,
      table_reader_options.level, table_reader_options.immortal,
      table_reader_options.largest_seqno, &tail_prefetch_stats_);
}

TableBuilder* BlockBasedTableFactory::NewTableBuilder(
    const TableBuilderOptions& table_builder_options, uint32_t column_family_id,
    WritableFileWriter* file) const {
  auto table_builder = new BlockBasedTableBuilder(
      table_builder_options.ioptions, table_builder_options.moptions,
      table_options_, table_builder_options.internal_comparator,
      table_builder_options.int_tbl_prop_collector_factories, column_family_id,
      file, table_builder_options.compression_type,
      table_builder_options.compression_opts,
      table_builder_options.skip_filters,
      table_builder_options.column_family_name,
      table_builder_options.creation_time,
      table_builder_options.oldest_key_time,
      table_builder_options.target_file_size);

  return table_builder;
}

Status BlockBasedTableFactory::SanitizeOptions(
    const DBOptions& /*db_opts*/, const ColumnFamilyOptions& cf_opts) const {
  if (table_options_.index_type == BlockBasedTableOptions::kHashSearch &&
      cf_opts.prefix_extractor == nullptr) {
    return Status::InvalidArgument(
        "Hash index is specified for block-based "
        "table, but prefix_extractor is not given");
  }
  if (table_options_.cache_index_and_filter_blocks &&
      table_options_.no_block_cache) {
    return Status::InvalidArgument(
        "Enable cache_index_and_filter_blocks, "
        ", but block cache is disabled");
  }
  if (table_options_.pin_l0_filter_and_index_blocks_in_cache &&
      table_options_.no_block_cache) {
    return Status::InvalidArgument(
        "Enable pin_l0_filter_and_index_blocks_in_cache, "
        ", but block cache is disabled");
  }
  if (!BlockBasedTableSupportedVersion(table_options_.format_version)) {
    return Status::InvalidArgument(
        "Unsupported BlockBasedTable format_version. Please check "
        "include/rocksdb/table.h for more info");
  }
  if (table_options_.block_align && (cf_opts.compression != kNoCompression)) {
    return Status::InvalidArgument(
        "Enable block_align, but compression "
        "enabled");
  }
  if (table_options_.block_align &&
      (table_options_.block_size & (table_options_.block_size - 1))) {
    return Status::InvalidArgument(
        "Block alignment requested but block size is not a power of 2");
  }
  if (table_options_.data_block_index_type ==
          BlockBasedTableOptions::kDataBlockBinaryAndHash &&
      table_options_.data_block_hash_table_util_ratio <= 0) {
    return Status::InvalidArgument(
        "data_block_hash_table_util_ratio should be greater than 0 when "
        "data_block_index_type is set to kDataBlockBinaryAndHash");
  }
  return Status::OK();
}

std::string BlockBasedTableFactory::GetPrintableTableOptions() const {
  std::string ret;
  ret.reserve(20000);
  const int kBufferSize = 200;
  char buffer[kBufferSize];

  snprintf(buffer, kBufferSize, "  flush_block_policy_factory: %s (%p)\n",
           table_options_.flush_block_policy_factory->Name(),
           static_cast<void*>(table_options_.flush_block_policy_factory.get()));
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  cache_index_and_filter_blocks: %d\n",
           table_options_.cache_index_and_filter_blocks);
  ret.append(buffer);
  snprintf(buffer, kBufferSize,
           "  cache_index_and_filter_blocks_with_high_priority: %d\n",
           table_options_.cache_index_and_filter_blocks_with_high_priority);
  ret.append(buffer);
  snprintf(buffer, kBufferSize,
           "  pin_l0_filter_and_index_blocks_in_cache: %d\n",
           table_options_.pin_l0_filter_and_index_blocks_in_cache);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  pin_top_level_index_and_filter: %d\n",
           table_options_.pin_top_level_index_and_filter);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  index_type: %d\n",
           table_options_.index_type);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  data_block_index_type: %d\n",
           table_options_.data_block_index_type);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  data_block_hash_table_util_ratio: %lf\n",
           table_options_.data_block_hash_table_util_ratio);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  hash_index_allow_collision: %d\n",
           table_options_.hash_index_allow_collision);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  checksum: %d\n", table_options_.checksum);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  no_block_cache: %d\n",
           table_options_.no_block_cache);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  block_cache: %p\n",
           static_cast<void*>(table_options_.block_cache.get()));
  ret.append(buffer);
  if (table_options_.block_cache) {
    const char* block_cache_name = table_options_.block_cache->Name();
    if (block_cache_name != nullptr) {
      snprintf(buffer, kBufferSize, "  block_cache_name: %s\n",
               block_cache_name);
      ret.append(buffer);
    }
    ret.append("  block_cache_options:\n");
    ret.append(table_options_.block_cache->GetPrintableOptions());
  }
  snprintf(buffer, kBufferSize, "  block_cache_compressed: %p\n",
           static_cast<void*>(table_options_.block_cache_compressed.get()));
  ret.append(buffer);
  if (table_options_.block_cache_compressed) {
    const char* block_cache_compressed_name =
        table_options_.block_cache_compressed->Name();
    if (block_cache_compressed_name != nullptr) {
      snprintf(buffer, kBufferSize, "  block_cache_name: %s\n",
               block_cache_compressed_name);
      ret.append(buffer);
    }
    ret.append("  block_cache_compressed_options:\n");
    ret.append(table_options_.block_cache_compressed->GetPrintableOptions());
  }
  snprintf(buffer, kBufferSize, "  persistent_cache: %p\n",
           static_cast<void*>(table_options_.persistent_cache.get()));
  ret.append(buffer);
  if (table_options_.persistent_cache) {
    snprintf(buffer, kBufferSize, "  persistent_cache_options:\n");
    ret.append(buffer);
    ret.append(table_options_.persistent_cache->GetPrintableOptions());
  }
  snprintf(buffer, kBufferSize, "  block_size: %" ROCKSDB_PRIszt "\n",
           table_options_.block_size);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  block_size_deviation: %d\n",
           table_options_.block_size_deviation);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  block_restart_interval: %d\n",
           table_options_.block_restart_interval);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  index_block_restart_interval: %d\n",
           table_options_.index_block_restart_interval);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  metadata_block_size: %" PRIu64 "\n",
           table_options_.metadata_block_size);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  partition_filters: %d\n",
           table_options_.partition_filters);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  use_delta_encoding: %d\n",
           table_options_.use_delta_encoding);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  filter_policy: %s\n",
           table_options_.filter_policy == nullptr
               ? "nullptr"
               : table_options_.filter_policy->Name());
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  whole_key_filtering: %d\n",
           table_options_.whole_key_filtering);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  verify_compression: %d\n",
           table_options_.verify_compression);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  read_amp_bytes_per_bit: %d\n",
           table_options_.read_amp_bytes_per_bit);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  format_version: %d\n",
           table_options_.format_version);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  enable_index_compression: %d\n",
           table_options_.enable_index_compression);
  ret.append(buffer);
  snprintf(buffer, kBufferSize, "  block_align: %d\n",
           table_options_.block_align);
  ret.append(buffer);
  return ret;
}

#ifndef ROCKSDB_LITE
namespace {
bool SerializeSingleBlockBasedTableOption(
    std::string* opt_string, const BlockBasedTableOptions& bbt_options,
    const std::string& name, const std::string& delimiter) {
  auto iter = block_based_table_type_info.find(name);
  if (iter == block_based_table_type_info.end()) {
    return false;
  }
  auto& opt_info = iter->second;
  const char* opt_address =
      reinterpret_cast<const char*>(&bbt_options) + opt_info.offset;
  std::string value;
  bool result = SerializeSingleOptionHelper(opt_address, opt_info.type, &value);
  if (result) {
    *opt_string = name + "=" + value + delimiter;
  }
  return result;
}
}  // namespace

Status BlockBasedTableFactory::GetOptionString(
    std::string* opt_string, const std::string& delimiter) const {
  assert(opt_string);
  opt_string->clear();
  for (auto iter = block_based_table_type_info.begin();
       iter != block_based_table_type_info.end(); ++iter) {
    if (iter->second.verification == OptionVerificationType::kDeprecated) {
      // If the option is no longer used in rocksdb and marked as deprecated,
      // we skip it in the serialization.
      continue;
    }
    std::string single_output;
    bool result = SerializeSingleBlockBasedTableOption(
        &single_output, table_options_, iter->first, delimiter);
    assert(result);
    if (result) {
      opt_string->append(single_output);
    }
  }
  return Status::OK();
}
#else
Status BlockBasedTableFactory::GetOptionString(
    std::string* /*opt_string*/, const std::string& /*delimiter*/) const {
  return Status::OK();
}
#endif  // !ROCKSDB_LITE

const BlockBasedTableOptions& BlockBasedTableFactory::table_options() const {
  return table_options_;
}

#ifndef ROCKSDB_LITE
namespace {
std::string ParseBlockBasedTableOption(const std::string& name,
                                       const std::string& org_value,
                                       BlockBasedTableOptions* new_options,
                                       bool input_strings_escaped = false,
                                       bool ignore_unknown_options = false) {
  const std::string& value =
      input_strings_escaped ? UnescapeOptionString(org_value) : org_value;
  if (!input_strings_escaped) {
    // if the input string is not escaped, it means this function is
    // invoked from SetOptions, which takes the old format.
    if (name == "block_cache" || name == "block_cache_compressed") {
      // cache options can be specified in the following format
      //   "block_cache={capacity=1M;num_shard_bits=4;
      //    strict_capacity_limit=true;high_pri_pool_ratio=0.5;}"
      // To support backward compatibility, the following format
      // is also supported.
      //   "block_cache=1M"
      std::shared_ptr<Cache> cache;
      // block_cache is specified in format block_cache=<cache_size>.
      if (value.find('=') == std::string::npos) {
        cache = NewLRUCache(ParseSizeT(value));
      } else {
        LRUCacheOptions cache_opts;
        if (!ParseOptionHelper(reinterpret_cast<char*>(&cache_opts),
                               OptionType::kLRUCacheOptions, value)) {
          return "Invalid cache options";
        }
        cache = NewLRUCache(cache_opts);
      }

      if (name == "block_cache") {
        new_options->block_cache = cache;
      } else {
        new_options->block_cache_compressed = cache;
      }
      return "";
    } else if (name == "filter_policy") {
      // Expect the following format
      // bloomfilter:int:bool
      const std::string kName = "bloomfilter:";
      if (value.compare(0, kName.size(), kName) != 0) {
        return "Invalid filter policy name";
      }
      size_t pos = value.find(':', kName.size());
      if (pos == std::string::npos) {
        return "Invalid filter policy config, missing bits_per_key";
      }
      int bits_per_key =
          ParseInt(trim(value.substr(kName.size(), pos - kName.size())));
      bool use_block_based_builder =
          ParseBoolean("use_block_based_builder", trim(value.substr(pos + 1)));
      new_options->filter_policy.reset(
          NewBloomFilterPolicy(bits_per_key, use_block_based_builder));
      return "";
    }
  }
  const auto iter = block_based_table_type_info.find(name);
  if (iter == block_based_table_type_info.end()) {
    if (ignore_unknown_options) {
      return "";
    } else {
      return "Unrecognized option";
    }
  }
  const auto& opt_info = iter->second;
  if (opt_info.verification != OptionVerificationType::kDeprecated &&
      !ParseOptionHelper(reinterpret_cast<char*>(new_options) + opt_info.offset,
                         opt_info.type, value)) {
    return "Invalid value";
  }
  return "";
}
}  // namespace

Status GetBlockBasedTableOptionsFromString(
    const BlockBasedTableOptions& table_options, const std::string& opts_str,
    BlockBasedTableOptions* new_table_options) {
  std::unordered_map<std::string, std::string> opts_map;
  Status s = StringToMap(opts_str, &opts_map);
  if (!s.ok()) {
    return s;
  }

  return GetBlockBasedTableOptionsFromMap(table_options, opts_map,
                                          new_table_options);
}

Status GetBlockBasedTableOptionsFromMap(
    const BlockBasedTableOptions& table_options,
    const std::unordered_map<std::string, std::string>& opts_map,
    BlockBasedTableOptions* new_table_options, bool input_strings_escaped,
    bool ignore_unknown_options) {
  assert(new_table_options);
  *new_table_options = table_options;
  for (const auto& o : opts_map) {
    auto error_message = ParseBlockBasedTableOption(
        o.first, o.second, new_table_options, input_strings_escaped,
        ignore_unknown_options);
    if (error_message != "") {
      const auto iter = block_based_table_type_info.find(o.first);
      if (iter == block_based_table_type_info.end() ||
          !input_strings_escaped ||  // !input_strings_escaped indicates
                                     // the old API, where everything is
                                     // parsable.
          (iter->second.verification != OptionVerificationType::kByName &&
           iter->second.verification !=
               OptionVerificationType::kByNameAllowNull &&
           iter->second.verification !=
               OptionVerificationType::kByNameAllowFromNull &&
           iter->second.verification != OptionVerificationType::kDeprecated)) {
        // Restore "new_options" to the default "base_options".
        *new_table_options = table_options;
        return Status::InvalidArgument("Can't parse BlockBasedTableOptions:",
                                       o.first + " " + error_message);
      }
    }
  }
  return Status::OK();
}

Status VerifyBlockBasedTableFactory(
    const BlockBasedTableFactory* base_tf,
    const BlockBasedTableFactory* file_tf,
    OptionsSanityCheckLevel sanity_check_level) {
  if ((base_tf != nullptr) != (file_tf != nullptr) &&
      sanity_check_level > kSanityLevelNone) {
    return Status::Corruption(
        "[RocksDBOptionsParser]: Inconsistent TableFactory class type");
  }
  if (base_tf == nullptr) {
    return Status::OK();
  }
  assert(file_tf != nullptr);

  const auto& base_opt = base_tf->table_options();
  const auto& file_opt = file_tf->table_options();

  for (auto& pair : block_based_table_type_info) {
    if (pair.second.verification == OptionVerificationType::kDeprecated) {
      // We skip checking deprecated variables as they might
      // contain random values since they might not be initialized
      continue;
    }
    if (BBTOptionSanityCheckLevel(pair.first) <= sanity_check_level) {
      if (!AreEqualOptions(reinterpret_cast<const char*>(&base_opt),
                           reinterpret_cast<const char*>(&file_opt),
                           pair.second, pair.first, nullptr)) {
        return Status::Corruption(
            "[RocksDBOptionsParser]: "
            "failed the verification on BlockBasedTableOptions::",
            pair.first);
      }
    }
  }
  return Status::OK();
}
#endif  // !ROCKSDB_LITE

TableFactory* NewBlockBasedTableFactory(
    const BlockBasedTableOptions& _table_options) {
  return new BlockBasedTableFactory(_table_options);
}

const std::string BlockBasedTableFactory::kName = "BlockBasedTable";
const std::string BlockBasedTablePropertyNames::kIndexType =
    "rocksdb.block.based.table.index.type";
const std::string BlockBasedTablePropertyNames::kWholeKeyFiltering =
    "rocksdb.block.based.table.whole.key.filtering";
const std::string BlockBasedTablePropertyNames::kPrefixFiltering =
    "rocksdb.block.based.table.prefix.filtering";
const std::string kHashIndexPrefixesBlock = "rocksdb.hashindex.prefixes";
const std::string kHashIndexPrefixesMetadataBlock =
    "rocksdb.hashindex.metadata";
const std::string kPropTrue = "1";
const std::string kPropFalse = "0";

}  // namespace rocksdb