rocksdb/options/options.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 "rocksdb/options.h"

#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif

#include <inttypes.h>
#include <limits>

#include "monitoring/statistics.h"
#include "options/db_options.h"
#include "options/options_helper.h"
#include "rocksdb/cache.h"
#include "rocksdb/compaction_filter.h"
#include "rocksdb/comparator.h"
#include "rocksdb/env.h"
#include "rocksdb/memtablerep.h"
#include "rocksdb/merge_operator.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "rocksdb/sst_file_manager.h"
#include "rocksdb/table.h"
#include "rocksdb/table_properties.h"
#include "rocksdb/wal_filter.h"
#include "table/block_based_table_factory.h"
#include "util/compression.h"

namespace rocksdb {

AdvancedColumnFamilyOptions::AdvancedColumnFamilyOptions() {
  assert(memtable_factory.get() != nullptr);
}

AdvancedColumnFamilyOptions::AdvancedColumnFamilyOptions(const Options& options)
    : max_write_buffer_number(options.max_write_buffer_number),
      min_write_buffer_number_to_merge(
          options.min_write_buffer_number_to_merge),
      max_write_buffer_number_to_maintain(
          options.max_write_buffer_number_to_maintain),
      inplace_update_support(options.inplace_update_support),
      inplace_update_num_locks(options.inplace_update_num_locks),
      inplace_callback(options.inplace_callback),
      memtable_prefix_bloom_size_ratio(
          options.memtable_prefix_bloom_size_ratio),
      memtable_huge_page_size(options.memtable_huge_page_size),
      memtable_insert_with_hint_prefix_extractor(
          options.memtable_insert_with_hint_prefix_extractor),
      bloom_locality(options.bloom_locality),
      arena_block_size(options.arena_block_size),
      compression_per_level(options.compression_per_level),
      num_levels(options.num_levels),
      level0_slowdown_writes_trigger(options.level0_slowdown_writes_trigger),
      level0_stop_writes_trigger(options.level0_stop_writes_trigger),
      target_file_size_base(options.target_file_size_base),
      target_file_size_multiplier(options.target_file_size_multiplier),
      level_compaction_dynamic_level_bytes(
          options.level_compaction_dynamic_level_bytes),
      max_bytes_for_level_multiplier(options.max_bytes_for_level_multiplier),
      max_bytes_for_level_multiplier_additional(
          options.max_bytes_for_level_multiplier_additional),
      max_compaction_bytes(options.max_compaction_bytes),
      soft_pending_compaction_bytes_limit(
          options.soft_pending_compaction_bytes_limit),
      hard_pending_compaction_bytes_limit(
          options.hard_pending_compaction_bytes_limit),
      compaction_style(options.compaction_style),
      compaction_pri(options.compaction_pri),
      compaction_options_universal(options.compaction_options_universal),
      compaction_options_fifo(options.compaction_options_fifo),
      max_sequential_skip_in_iterations(
          options.max_sequential_skip_in_iterations),
      memtable_factory(options.memtable_factory),
      table_properties_collector_factories(
          options.table_properties_collector_factories),
      max_successive_merges(options.max_successive_merges),
      optimize_filters_for_hits(options.optimize_filters_for_hits),
      paranoid_file_checks(options.paranoid_file_checks),
      force_consistency_checks(options.force_consistency_checks),
      report_bg_io_stats(options.report_bg_io_stats),
      ttl(options.ttl) {
  assert(memtable_factory.get() != nullptr);
  if (max_bytes_for_level_multiplier_additional.size() <
      static_cast<unsigned int>(num_levels)) {
    max_bytes_for_level_multiplier_additional.resize(num_levels, 1);
  }
}

ColumnFamilyOptions::ColumnFamilyOptions()
    : compression(Snappy_Supported() ? kSnappyCompression : kNoCompression),
      table_factory(
          std::shared_ptr<TableFactory>(new BlockBasedTableFactory())) {}

ColumnFamilyOptions::ColumnFamilyOptions(const Options& options)
    : ColumnFamilyOptions(*static_cast<const ColumnFamilyOptions*>(&options)) {}

DBOptions::DBOptions() {}
DBOptions::DBOptions(const Options& options)
    : DBOptions(*static_cast<const DBOptions*>(&options)) {}

void DBOptions::Dump(Logger* log) const {
    ImmutableDBOptions(*this).Dump(log);
    MutableDBOptions(*this).Dump(log);
}  // DBOptions::Dump

void ColumnFamilyOptions::Dump(Logger* log) const {
  ROCKS_LOG_HEADER(log, "              Options.comparator: %s",
                   comparator->Name());
  ROCKS_LOG_HEADER(log, "          Options.merge_operator: %s",
                   merge_operator ? merge_operator->Name() : "None");
  ROCKS_LOG_HEADER(log, "       Options.compaction_filter: %s",
                   compaction_filter ? compaction_filter->Name() : "None");
  ROCKS_LOG_HEADER(
      log, "       Options.compaction_filter_factory: %s",
      compaction_filter_factory ? compaction_filter_factory->Name() : "None");
  ROCKS_LOG_HEADER(log, "        Options.memtable_factory: %s",
                   memtable_factory->Name());
  ROCKS_LOG_HEADER(log, "           Options.table_factory: %s",
                   table_factory->Name());
  ROCKS_LOG_HEADER(log, "           table_factory options: %s",
                   table_factory->GetPrintableTableOptions().c_str());
  ROCKS_LOG_HEADER(log, "       Options.write_buffer_size: %" ROCKSDB_PRIszt,
                   write_buffer_size);
  ROCKS_LOG_HEADER(log, " Options.max_write_buffer_number: %d",
                   max_write_buffer_number);
  if (!compression_per_level.empty()) {
    for (unsigned int i = 0; i < compression_per_level.size(); i++) {
      ROCKS_LOG_HEADER(
          log, "       Options.compression[%d]: %s", i,
          CompressionTypeToString(compression_per_level[i]).c_str());
    }
    } else {
      ROCKS_LOG_HEADER(log, "         Options.compression: %s",
                       CompressionTypeToString(compression).c_str());
    }
    ROCKS_LOG_HEADER(
        log, "                 Options.bottommost_compression: %s",
        bottommost_compression == kDisableCompressionOption
            ? "Disabled"
            : CompressionTypeToString(bottommost_compression).c_str());
    ROCKS_LOG_HEADER(
        log, "      Options.prefix_extractor: %s",
        prefix_extractor == nullptr ? "nullptr" : prefix_extractor->Name());
    ROCKS_LOG_HEADER(log,
                     "  Options.memtable_insert_with_hint_prefix_extractor: %s",
                     memtable_insert_with_hint_prefix_extractor == nullptr
                         ? "nullptr"
                         : memtable_insert_with_hint_prefix_extractor->Name());
    ROCKS_LOG_HEADER(log, "            Options.num_levels: %d", num_levels);
    ROCKS_LOG_HEADER(log, "       Options.min_write_buffer_number_to_merge: %d",
                     min_write_buffer_number_to_merge);
    ROCKS_LOG_HEADER(log, "    Options.max_write_buffer_number_to_maintain: %d",
                     max_write_buffer_number_to_maintain);
    ROCKS_LOG_HEADER(
        log, "           Options.bottommost_compression_opts.window_bits: %d",
        bottommost_compression_opts.window_bits);
    ROCKS_LOG_HEADER(
        log, "                 Options.bottommost_compression_opts.level: %d",
        bottommost_compression_opts.level);
    ROCKS_LOG_HEADER(
        log, "              Options.bottommost_compression_opts.strategy: %d",
        bottommost_compression_opts.strategy);
    ROCKS_LOG_HEADER(
        log,
        "        Options.bottommost_compression_opts.max_dict_bytes: "
        "%" ROCKSDB_PRIszt,
        bottommost_compression_opts.max_dict_bytes);
    ROCKS_LOG_HEADER(
        log,
        "        Options.bottommost_compression_opts.zstd_max_train_bytes: "
        "%" ROCKSDB_PRIszt,
        bottommost_compression_opts.zstd_max_train_bytes);
    ROCKS_LOG_HEADER(
        log, "                 Options.bottommost_compression_opts.enabled: %s",
        bottommost_compression_opts.enabled ? "true" : "false");
    ROCKS_LOG_HEADER(log, "           Options.compression_opts.window_bits: %d",
                     compression_opts.window_bits);
    ROCKS_LOG_HEADER(log, "                 Options.compression_opts.level: %d",
                     compression_opts.level);
    ROCKS_LOG_HEADER(log, "              Options.compression_opts.strategy: %d",
                     compression_opts.strategy);
    ROCKS_LOG_HEADER(
        log,
        "        Options.compression_opts.max_dict_bytes: %" ROCKSDB_PRIszt,
        compression_opts.max_dict_bytes);
    ROCKS_LOG_HEADER(log,
                     "        Options.compression_opts.zstd_max_train_bytes: "
                     "%" ROCKSDB_PRIszt,
                     compression_opts.zstd_max_train_bytes);
    ROCKS_LOG_HEADER(log,
                     "                 Options.compression_opts.enabled: %s",
                     compression_opts.enabled ? "true" : "false");
    ROCKS_LOG_HEADER(log, "     Options.level0_file_num_compaction_trigger: %d",
                     level0_file_num_compaction_trigger);
    ROCKS_LOG_HEADER(log, "         Options.level0_slowdown_writes_trigger: %d",
                     level0_slowdown_writes_trigger);
    ROCKS_LOG_HEADER(log, "             Options.level0_stop_writes_trigger: %d",
                     level0_stop_writes_trigger);
    ROCKS_LOG_HEADER(
        log, "                  Options.target_file_size_base: %" PRIu64,
        target_file_size_base);
    ROCKS_LOG_HEADER(log, "            Options.target_file_size_multiplier: %d",
                     target_file_size_multiplier);
    ROCKS_LOG_HEADER(
        log, "               Options.max_bytes_for_level_base: %" PRIu64,
        max_bytes_for_level_base);
    ROCKS_LOG_HEADER(log, "Options.level_compaction_dynamic_level_bytes: %d",
                     level_compaction_dynamic_level_bytes);
    ROCKS_LOG_HEADER(log, "         Options.max_bytes_for_level_multiplier: %f",
                     max_bytes_for_level_multiplier);
    for (size_t i = 0; i < max_bytes_for_level_multiplier_additional.size();
         i++) {
      ROCKS_LOG_HEADER(
          log, "Options.max_bytes_for_level_multiplier_addtl[%" ROCKSDB_PRIszt
               "]: %d",
          i, max_bytes_for_level_multiplier_additional[i]);
    }
    ROCKS_LOG_HEADER(
        log, "      Options.max_sequential_skip_in_iterations: %" PRIu64,
        max_sequential_skip_in_iterations);
    ROCKS_LOG_HEADER(
        log, "                   Options.max_compaction_bytes: %" PRIu64,
        max_compaction_bytes);
    ROCKS_LOG_HEADER(
        log,
        "                       Options.arena_block_size: %" ROCKSDB_PRIszt,
        arena_block_size);
    ROCKS_LOG_HEADER(log,
                     "  Options.soft_pending_compaction_bytes_limit: %" PRIu64,
                     soft_pending_compaction_bytes_limit);
    ROCKS_LOG_HEADER(log,
                     "  Options.hard_pending_compaction_bytes_limit: %" PRIu64,
                     hard_pending_compaction_bytes_limit);
    ROCKS_LOG_HEADER(log, "      Options.rate_limit_delay_max_milliseconds: %u",
                     rate_limit_delay_max_milliseconds);
    ROCKS_LOG_HEADER(log, "               Options.disable_auto_compactions: %d",
                     disable_auto_compactions);

    const auto& it_compaction_style =
        compaction_style_to_string.find(compaction_style);
    std::string str_compaction_style;
    if (it_compaction_style == compaction_style_to_string.end()) {
      assert(false);
      str_compaction_style = "unknown_" + std::to_string(compaction_style);
    } else {
      str_compaction_style = it_compaction_style->second;
    }
    ROCKS_LOG_HEADER(log,
                     "                       Options.compaction_style: %s",
                     str_compaction_style.c_str());

    const auto& it_compaction_pri =
        compaction_pri_to_string.find(compaction_pri);
    std::string str_compaction_pri;
    if (it_compaction_pri == compaction_pri_to_string.end()) {
      assert(false);
      str_compaction_pri = "unknown_" + std::to_string(compaction_pri);
    } else {
      str_compaction_pri = it_compaction_pri->second;
    }
    ROCKS_LOG_HEADER(log,
                     "                         Options.compaction_pri: %s",
                     str_compaction_pri.c_str());
    ROCKS_LOG_HEADER(log,
                     "Options.compaction_options_universal.size_ratio: %u",
                     compaction_options_universal.size_ratio);
    ROCKS_LOG_HEADER(log,
                     "Options.compaction_options_universal.min_merge_width: %u",
                     compaction_options_universal.min_merge_width);
    ROCKS_LOG_HEADER(log,
                     "Options.compaction_options_universal.max_merge_width: %u",
                     compaction_options_universal.max_merge_width);
    ROCKS_LOG_HEADER(
        log,
        "Options.compaction_options_universal."
        "max_size_amplification_percent: %u",
        compaction_options_universal.max_size_amplification_percent);
    ROCKS_LOG_HEADER(
        log,
        "Options.compaction_options_universal.compression_size_percent: %d",
        compaction_options_universal.compression_size_percent);
    const auto& it_compaction_stop_style = compaction_stop_style_to_string.find(
        compaction_options_universal.stop_style);
    std::string str_compaction_stop_style;
    if (it_compaction_stop_style == compaction_stop_style_to_string.end()) {
      assert(false);
      str_compaction_stop_style =
          "unknown_" + std::to_string(compaction_options_universal.stop_style);
    } else {
      str_compaction_stop_style = it_compaction_stop_style->second;
    }
    ROCKS_LOG_HEADER(log,
                     "Options.compaction_options_universal.stop_style: %s",
                     str_compaction_stop_style.c_str());
    ROCKS_LOG_HEADER(
        log, "Options.compaction_options_fifo.max_table_files_size: %" PRIu64,
        compaction_options_fifo.max_table_files_size);
    ROCKS_LOG_HEADER(log,
                     "Options.compaction_options_fifo.allow_compaction: %d",
                     compaction_options_fifo.allow_compaction);
    ROCKS_LOG_HEADER(log, "Options.compaction_options_fifo.ttl: %" PRIu64,
                     compaction_options_fifo.ttl);
    std::string collector_names;
    for (const auto& collector_factory : table_properties_collector_factories) {
      collector_names.append(collector_factory->Name());
      collector_names.append("; ");
    }
    ROCKS_LOG_HEADER(
        log, "                  Options.table_properties_collectors: %s",
        collector_names.c_str());
    ROCKS_LOG_HEADER(log,
                     "                  Options.inplace_update_support: %d",
                     inplace_update_support);
    ROCKS_LOG_HEADER(
        log,
        "                Options.inplace_update_num_locks: %" ROCKSDB_PRIszt,
        inplace_update_num_locks);
    // TODO: easier config for bloom (maybe based on avg key/value size)
    ROCKS_LOG_HEADER(
        log, "              Options.memtable_prefix_bloom_size_ratio: %f",
        memtable_prefix_bloom_size_ratio);

    ROCKS_LOG_HEADER(log, "  Options.memtable_huge_page_size: %" ROCKSDB_PRIszt,
                     memtable_huge_page_size);
    ROCKS_LOG_HEADER(log,
                     "                          Options.bloom_locality: %d",
                     bloom_locality);

    ROCKS_LOG_HEADER(
        log,
        "                   Options.max_successive_merges: %" ROCKSDB_PRIszt,
        max_successive_merges);
    ROCKS_LOG_HEADER(log,
                     "               Options.optimize_filters_for_hits: %d",
                     optimize_filters_for_hits);
    ROCKS_LOG_HEADER(log, "               Options.paranoid_file_checks: %d",
                     paranoid_file_checks);
    ROCKS_LOG_HEADER(log, "               Options.force_consistency_checks: %d",
                     force_consistency_checks);
    ROCKS_LOG_HEADER(log, "               Options.report_bg_io_stats: %d",
                     report_bg_io_stats);
    ROCKS_LOG_HEADER(log, "                              Options.ttl: %d", ttl);
}  // ColumnFamilyOptions::Dump

void Options::Dump(Logger* log) const {
  DBOptions::Dump(log);
  ColumnFamilyOptions::Dump(log);
}   // Options::Dump

void Options::DumpCFOptions(Logger* log) const {
  ColumnFamilyOptions::Dump(log);
}  // Options::DumpCFOptions

//
// The goal of this method is to create a configuration that
// allows an application to write all files into L0 and
// then do a single compaction to output all files into L1.
Options*
Options::PrepareForBulkLoad()
{
  // never slowdown ingest.
  level0_file_num_compaction_trigger = (1<<30);
  level0_slowdown_writes_trigger = (1<<30);
  level0_stop_writes_trigger = (1<<30);
  soft_pending_compaction_bytes_limit = 0;
  hard_pending_compaction_bytes_limit = 0;

  // no auto compactions please. The application should issue a
  // manual compaction after all data is loaded into L0.
  disable_auto_compactions = true;
  // A manual compaction run should pick all files in L0 in
  // a single compaction run.
  max_compaction_bytes = (static_cast<uint64_t>(1) << 60);

  // It is better to have only 2 levels, otherwise a manual
  // compaction would compact at every possible level, thereby
  // increasing the total time needed for compactions.
  num_levels = 2;

  // Need to allow more write buffers to allow more parallism
  // of flushes.
  max_write_buffer_number = 6;
  min_write_buffer_number_to_merge = 1;

  // When compaction is disabled, more parallel flush threads can
  // help with write throughput.
  max_background_flushes = 4;

  // Prevent a memtable flush to automatically promote files
  // to L1. This is helpful so that all files that are
  // input to the manual compaction are all at L0.
  max_background_compactions = 2;

  // The compaction would create large files in L1.
  target_file_size_base = 256 * 1024 * 1024;
  return this;
}

Options* Options::OptimizeForSmallDb() {
  ColumnFamilyOptions::OptimizeForSmallDb();
  DBOptions::OptimizeForSmallDb();
  return this;
}

Options* Options::OldDefaults(int rocksdb_major_version,
                              int rocksdb_minor_version) {
  ColumnFamilyOptions::OldDefaults(rocksdb_major_version,
                                   rocksdb_minor_version);
  DBOptions::OldDefaults(rocksdb_major_version, rocksdb_minor_version);
  return this;
}

DBOptions* DBOptions::OldDefaults(int rocksdb_major_version,
                                  int rocksdb_minor_version) {
  if (rocksdb_major_version < 4 ||
      (rocksdb_major_version == 4 && rocksdb_minor_version < 7)) {
    max_file_opening_threads = 1;
    table_cache_numshardbits = 4;
  }
  if (rocksdb_major_version < 5 ||
      (rocksdb_major_version == 5 && rocksdb_minor_version < 2)) {
    delayed_write_rate = 2 * 1024U * 1024U;
  } else if (rocksdb_major_version < 5 ||
             (rocksdb_major_version == 5 && rocksdb_minor_version < 6)) {
    delayed_write_rate = 16 * 1024U * 1024U;
  }
  max_open_files = 5000;
  wal_recovery_mode = WALRecoveryMode::kTolerateCorruptedTailRecords;
  return this;
}

ColumnFamilyOptions* ColumnFamilyOptions::OldDefaults(
    int rocksdb_major_version, int rocksdb_minor_version) {
  if (rocksdb_major_version < 4 ||
      (rocksdb_major_version == 4 && rocksdb_minor_version < 7)) {
    write_buffer_size = 4 << 20;
    target_file_size_base = 2 * 1048576;
    max_bytes_for_level_base = 10 * 1048576;
    soft_pending_compaction_bytes_limit = 0;
    hard_pending_compaction_bytes_limit = 0;
  }
  if (rocksdb_major_version < 5) {
    level0_stop_writes_trigger = 24;
  } else if (rocksdb_major_version == 5 && rocksdb_minor_version < 2) {
    level0_stop_writes_trigger = 30;
  }
  compaction_pri = CompactionPri::kByCompensatedSize;

  return this;
}

// Optimization functions
DBOptions* DBOptions::OptimizeForSmallDb() {
  max_file_opening_threads = 1;
  max_open_files = 5000;
  return this;
}

ColumnFamilyOptions* ColumnFamilyOptions::OptimizeForSmallDb() {
  write_buffer_size = 2 << 20;
  target_file_size_base = 2 * 1048576;
  max_bytes_for_level_base = 10 * 1048576;
  soft_pending_compaction_bytes_limit = 256 * 1048576;
  hard_pending_compaction_bytes_limit = 1073741824ul;
  return this;
}

#ifndef ROCKSDB_LITE
ColumnFamilyOptions* ColumnFamilyOptions::OptimizeForPointLookup(
    uint64_t block_cache_size_mb) {
  prefix_extractor.reset(NewNoopTransform());
  BlockBasedTableOptions block_based_options;
  block_based_options.index_type = BlockBasedTableOptions::kHashSearch;
  block_based_options.data_block_index_type =
      BlockBasedTableOptions::kDataBlockBinaryAndHash;
  block_based_options.data_block_hash_table_util_ratio = 0.75;
  block_based_options.filter_policy.reset(NewBloomFilterPolicy(10));
  block_based_options.block_cache =
      NewLRUCache(static_cast<size_t>(block_cache_size_mb * 1024 * 1024));
  table_factory.reset(new BlockBasedTableFactory(block_based_options));
  memtable_prefix_bloom_size_ratio = 0.02;
  return this;
}

ColumnFamilyOptions* ColumnFamilyOptions::OptimizeLevelStyleCompaction(
    uint64_t memtable_memory_budget) {
  write_buffer_size = static_cast<size_t>(memtable_memory_budget / 4);
  // merge two memtables when flushing to L0
  min_write_buffer_number_to_merge = 2;
  // this means we'll use 50% extra memory in the worst case, but will reduce
  // write stalls.
  max_write_buffer_number = 6;
  // start flushing L0->L1 as soon as possible. each file on level0 is
  // (memtable_memory_budget / 2). This will flush level 0 when it's bigger than
  // memtable_memory_budget.
  level0_file_num_compaction_trigger = 2;
  // doesn't really matter much, but we don't want to create too many files
  target_file_size_base = memtable_memory_budget / 8;
  // make Level1 size equal to Level0 size, so that L0->L1 compactions are fast
  max_bytes_for_level_base = memtable_memory_budget;

  // level style compaction
  compaction_style = kCompactionStyleLevel;

  // only compress levels >= 2
  compression_per_level.resize(num_levels);
  for (int i = 0; i < num_levels; ++i) {
    if (i < 2) {
      compression_per_level[i] = kNoCompression;
    } else {
      compression_per_level[i] = kSnappyCompression;
    }
  }
  return this;
}

ColumnFamilyOptions* ColumnFamilyOptions::OptimizeUniversalStyleCompaction(
    uint64_t memtable_memory_budget) {
  write_buffer_size = static_cast<size_t>(memtable_memory_budget / 4);
  // merge two memtables when flushing to L0
  min_write_buffer_number_to_merge = 2;
  // this means we'll use 50% extra memory in the worst case, but will reduce
  // write stalls.
  max_write_buffer_number = 6;
  // universal style compaction
  compaction_style = kCompactionStyleUniversal;
  compaction_options_universal.compression_size_percent = 80;
  return this;
}

DBOptions* DBOptions::IncreaseParallelism(int total_threads) {
  max_background_jobs = total_threads;
  env->SetBackgroundThreads(total_threads, Env::LOW);
  env->SetBackgroundThreads(1, Env::HIGH);
  return this;
}

#endif  // !ROCKSDB_LITE

ReadOptions::ReadOptions()
    : snapshot(nullptr),
      iterate_lower_bound(nullptr),
      iterate_upper_bound(nullptr),
      readahead_size(0),
      max_skippable_internal_keys(0),
      read_tier(kReadAllTier),
      verify_checksums(true),
      fill_cache(true),
      tailing(false),
      managed(false),
      total_order_seek(false),
      prefix_same_as_start(false),
      pin_data(false),
      background_purge_on_iterator_cleanup(false),
      ignore_range_deletions(false),
      iter_start_seqnum(0) {}

ReadOptions::ReadOptions(bool cksum, bool cache)
    : snapshot(nullptr),
      iterate_lower_bound(nullptr),
      iterate_upper_bound(nullptr),
      readahead_size(0),
      max_skippable_internal_keys(0),
      read_tier(kReadAllTier),
      verify_checksums(cksum),
      fill_cache(cache),
      tailing(false),
      managed(false),
      total_order_seek(false),
      prefix_same_as_start(false),
      pin_data(false),
      background_purge_on_iterator_cleanup(false),
      ignore_range_deletions(false),
      iter_start_seqnum(0) {}

}  // namespace rocksdb