rocksdb/db/internal_stats.h

//  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.
//

#pragma once

#include <map>
#include <memory>
#include <string>
#include <vector>

#include "cache/cache_entry_roles.h"
#include "db/version_set.h"
#include "rocksdb/system_clock.h"
#include "util/hash_containers.h"

namespace ROCKSDB_NAMESPACE {

template <class Stats>
class CacheEntryStatsCollector;
class DBImpl;
class MemTableList;

// Config for retrieving a property's value.
struct DBPropertyInfo {
  bool need_out_of_mutex;

  // gcc had an internal error for initializing union of pointer-to-member-
  // functions. Workaround is to populate exactly one of the following function
  // pointers with a non-nullptr value.

  // @param value Value-result argument for storing the property's string value
  // @param suffix Argument portion of the property. For example, suffix would
  //      be "5" for the property "rocksdb.num-files-at-level5". So far, only
  //      certain string properties take an argument.
  bool (InternalStats::*handle_string)(std::string* value, Slice suffix);

  // @param value Value-result argument for storing the property's uint64 value
  // @param db Many of the int properties rely on DBImpl methods.
  // @param version Version is needed in case the property is retrieved without
  //      holding db mutex, which is only supported for int properties.
  bool (InternalStats::*handle_int)(uint64_t* value, DBImpl* db,
                                    Version* version);

  // @param props Map of general properties to populate
  // @param suffix Argument portion of the property. (see handle_string)
  bool (InternalStats::*handle_map)(std::map<std::string, std::string>* props,
                                    Slice suffix);

  // handle the string type properties rely on DBImpl methods
  // @param value Value-result argument for storing the property's string value
  bool (DBImpl::*handle_string_dbimpl)(std::string* value);
};

extern const DBPropertyInfo* GetPropertyInfo(const Slice& property);

#ifndef ROCKSDB_LITE
#undef SCORE
enum class LevelStatType {
  INVALID = 0,
  NUM_FILES,
  COMPACTED_FILES,
  SIZE_BYTES,
  SCORE,
  READ_GB,
  RN_GB,
  RNP1_GB,
  WRITE_GB,
  W_NEW_GB,
  MOVED_GB,
  WRITE_AMP,
  READ_MBPS,
  WRITE_MBPS,
  COMP_SEC,
  COMP_CPU_SEC,
  COMP_COUNT,
  AVG_SEC,
  KEY_IN,
  KEY_DROP,
  R_BLOB_GB,
  W_BLOB_GB,
  TOTAL  // total number of types
};

struct LevelStat {
  // This what will be L?.property_name in the flat map returned to the user
  std::string property_name;
  // This will be what we will print in the header in the cli
  std::string header_name;
};

struct DBStatInfo {
  // This what will be property_name in the flat map returned to the user
  std::string property_name;
};

class InternalStats {
 public:
  static const std::map<LevelStatType, LevelStat> compaction_level_stats;

  enum InternalCFStatsType {
    L0_FILE_COUNT_LIMIT_SLOWDOWNS,
    LOCKED_L0_FILE_COUNT_LIMIT_SLOWDOWNS,
    MEMTABLE_LIMIT_STOPS,
    MEMTABLE_LIMIT_SLOWDOWNS,
    L0_FILE_COUNT_LIMIT_STOPS,
    LOCKED_L0_FILE_COUNT_LIMIT_STOPS,
    PENDING_COMPACTION_BYTES_LIMIT_SLOWDOWNS,
    PENDING_COMPACTION_BYTES_LIMIT_STOPS,
    WRITE_STALLS_ENUM_MAX,
    BYTES_FLUSHED,
    BYTES_INGESTED_ADD_FILE,
    INGESTED_NUM_FILES_TOTAL,
    INGESTED_LEVEL0_NUM_FILES_TOTAL,
    INGESTED_NUM_KEYS_TOTAL,
    INTERNAL_CF_STATS_ENUM_MAX,
  };

  enum InternalDBStatsType {
    kIntStatsWalFileBytes,
    kIntStatsWalFileSynced,
    kIntStatsBytesWritten,
    kIntStatsNumKeysWritten,
    kIntStatsWriteDoneByOther,
    kIntStatsWriteDoneBySelf,
    kIntStatsWriteWithWal,
    kIntStatsWriteStallMicros,
    kIntStatsNumMax,
  };

  static const std::map<InternalDBStatsType, DBStatInfo> db_stats_type_to_info;

  InternalStats(int num_levels, SystemClock* clock, ColumnFamilyData* cfd);

  // Per level compaction stats
  struct CompactionOutputsStats {
    uint64_t num_output_records = 0;
    uint64_t bytes_written = 0;
    uint64_t bytes_written_blob = 0;
    uint64_t num_output_files = 0;
    uint64_t num_output_files_blob = 0;

    void Add(const CompactionOutputsStats& stats) {
      this->num_output_records += stats.num_output_records;
      this->bytes_written += stats.bytes_written;
      this->bytes_written_blob += stats.bytes_written_blob;
      this->num_output_files += stats.num_output_files;
      this->num_output_files_blob += stats.num_output_files_blob;
    }
  };

  // Per level compaction stats.  comp_stats_[level] stores the stats for
  // compactions that produced data for the specified "level".
  struct CompactionStats {
    uint64_t micros;
    uint64_t cpu_micros;

    // The number of bytes read from all non-output levels (table files)
    uint64_t bytes_read_non_output_levels;

    // The number of bytes read from the compaction output level (table files)
    uint64_t bytes_read_output_level;

    // The number of bytes read from blob files
    uint64_t bytes_read_blob;

    // Total number of bytes written to table files during compaction
    uint64_t bytes_written;

    // Total number of bytes written to blob files during compaction
    uint64_t bytes_written_blob;

    // Total number of bytes moved to the output level (table files)
    uint64_t bytes_moved;

    // The number of compaction input files in all non-output levels (table
    // files)
    int num_input_files_in_non_output_levels;

    // The number of compaction input files in the output level (table files)
    int num_input_files_in_output_level;

    // The number of compaction output files (table files)
    int num_output_files;

    // The number of compaction output files (blob files)
    int num_output_files_blob;

    // Total incoming entries during compaction between levels N and N+1
    uint64_t num_input_records;

    // Accumulated diff number of entries
    // (num input entries - num output entries) for compaction levels N and N+1
    uint64_t num_dropped_records;

    // Total output entries from compaction
    uint64_t num_output_records;

    // Number of compactions done
    int count;

    // Number of compactions done per CompactionReason
    int counts[static_cast<int>(CompactionReason::kNumOfReasons)]{};

    explicit CompactionStats()
        : micros(0),
          cpu_micros(0),
          bytes_read_non_output_levels(0),
          bytes_read_output_level(0),
          bytes_read_blob(0),
          bytes_written(0),
          bytes_written_blob(0),
          bytes_moved(0),
          num_input_files_in_non_output_levels(0),
          num_input_files_in_output_level(0),
          num_output_files(0),
          num_output_files_blob(0),
          num_input_records(0),
          num_dropped_records(0),
          num_output_records(0),
          count(0) {
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = 0;
      }
    }

    explicit CompactionStats(CompactionReason reason, int c)
        : micros(0),
          cpu_micros(0),
          bytes_read_non_output_levels(0),
          bytes_read_output_level(0),
          bytes_read_blob(0),
          bytes_written(0),
          bytes_written_blob(0),
          bytes_moved(0),
          num_input_files_in_non_output_levels(0),
          num_input_files_in_output_level(0),
          num_output_files(0),
          num_output_files_blob(0),
          num_input_records(0),
          num_dropped_records(0),
          num_output_records(0),
          count(c) {
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = 0;
      }
      int r = static_cast<int>(reason);
      if (r >= 0 && r < num_of_reasons) {
        counts[r] = c;
      } else {
        count = 0;
      }
    }

    CompactionStats(const CompactionStats& c)
        : micros(c.micros),
          cpu_micros(c.cpu_micros),
          bytes_read_non_output_levels(c.bytes_read_non_output_levels),
          bytes_read_output_level(c.bytes_read_output_level),
          bytes_read_blob(c.bytes_read_blob),
          bytes_written(c.bytes_written),
          bytes_written_blob(c.bytes_written_blob),
          bytes_moved(c.bytes_moved),
          num_input_files_in_non_output_levels(
              c.num_input_files_in_non_output_levels),
          num_input_files_in_output_level(c.num_input_files_in_output_level),
          num_output_files(c.num_output_files),
          num_output_files_blob(c.num_output_files_blob),
          num_input_records(c.num_input_records),
          num_dropped_records(c.num_dropped_records),
          num_output_records(c.num_output_records),
          count(c.count) {
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = c.counts[i];
      }
    }

    CompactionStats& operator=(const CompactionStats& c) {
      micros = c.micros;
      cpu_micros = c.cpu_micros;
      bytes_read_non_output_levels = c.bytes_read_non_output_levels;
      bytes_read_output_level = c.bytes_read_output_level;
      bytes_read_blob = c.bytes_read_blob;
      bytes_written = c.bytes_written;
      bytes_written_blob = c.bytes_written_blob;
      bytes_moved = c.bytes_moved;
      num_input_files_in_non_output_levels =
          c.num_input_files_in_non_output_levels;
      num_input_files_in_output_level = c.num_input_files_in_output_level;
      num_output_files = c.num_output_files;
      num_output_files_blob = c.num_output_files_blob;
      num_input_records = c.num_input_records;
      num_dropped_records = c.num_dropped_records;
      num_output_records = c.num_output_records;
      count = c.count;

      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = c.counts[i];
      }
      return *this;
    }

    void Clear() {
      this->micros = 0;
      this->cpu_micros = 0;
      this->bytes_read_non_output_levels = 0;
      this->bytes_read_output_level = 0;
      this->bytes_read_blob = 0;
      this->bytes_written = 0;
      this->bytes_written_blob = 0;
      this->bytes_moved = 0;
      this->num_input_files_in_non_output_levels = 0;
      this->num_input_files_in_output_level = 0;
      this->num_output_files = 0;
      this->num_output_files_blob = 0;
      this->num_input_records = 0;
      this->num_dropped_records = 0;
      this->num_output_records = 0;
      this->count = 0;
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = 0;
      }
    }

    void Add(const CompactionStats& c) {
      this->micros += c.micros;
      this->cpu_micros += c.cpu_micros;
      this->bytes_read_non_output_levels += c.bytes_read_non_output_levels;
      this->bytes_read_output_level += c.bytes_read_output_level;
      this->bytes_read_blob += c.bytes_read_blob;
      this->bytes_written += c.bytes_written;
      this->bytes_written_blob += c.bytes_written_blob;
      this->bytes_moved += c.bytes_moved;
      this->num_input_files_in_non_output_levels +=
          c.num_input_files_in_non_output_levels;
      this->num_input_files_in_output_level +=
          c.num_input_files_in_output_level;
      this->num_output_files += c.num_output_files;
      this->num_output_files_blob += c.num_output_files_blob;
      this->num_input_records += c.num_input_records;
      this->num_dropped_records += c.num_dropped_records;
      this->num_output_records += c.num_output_records;
      this->count += c.count;
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i< num_of_reasons; i++) {
        counts[i] += c.counts[i];
      }
    }

    void Add(const CompactionOutputsStats& stats) {
      this->num_output_files += static_cast<int>(stats.num_output_files);
      this->num_output_records += stats.num_output_records;
      this->bytes_written += stats.bytes_written;
      this->bytes_written_blob += stats.bytes_written_blob;
      this->num_output_files_blob +=
          static_cast<int>(stats.num_output_files_blob);
    }

    void Subtract(const CompactionStats& c) {
      this->micros -= c.micros;
      this->cpu_micros -= c.cpu_micros;
      this->bytes_read_non_output_levels -= c.bytes_read_non_output_levels;
      this->bytes_read_output_level -= c.bytes_read_output_level;
      this->bytes_read_blob -= c.bytes_read_blob;
      this->bytes_written -= c.bytes_written;
      this->bytes_written_blob -= c.bytes_written_blob;
      this->bytes_moved -= c.bytes_moved;
      this->num_input_files_in_non_output_levels -=
          c.num_input_files_in_non_output_levels;
      this->num_input_files_in_output_level -=
          c.num_input_files_in_output_level;
      this->num_output_files -= c.num_output_files;
      this->num_output_files_blob -= c.num_output_files_blob;
      this->num_input_records -= c.num_input_records;
      this->num_dropped_records -= c.num_dropped_records;
      this->num_output_records -= c.num_output_records;
      this->count -= c.count;
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] -= c.counts[i];
      }
    }

    void ResetCompactionReason(CompactionReason reason) {
      int num_of_reasons = static_cast<int>(CompactionReason::kNumOfReasons);
      assert(count == 1);  // only support update one compaction reason
      for (int i = 0; i < num_of_reasons; i++) {
        counts[i] = 0;
      }
      int r = static_cast<int>(reason);
      assert(r >= 0 && r < num_of_reasons);
      counts[r] = 1;
    }
  };

  // Compaction stats, for per_key_placement compaction, it includes 2 levels
  // stats: the last level and the penultimate level.
  struct CompactionStatsFull {
    // the stats for the target primary output level
    CompactionStats stats;

    // stats for penultimate level output if exist
    bool has_penultimate_level_output = false;
    CompactionStats penultimate_level_stats;

    explicit CompactionStatsFull() : stats(), penultimate_level_stats() {}

    explicit CompactionStatsFull(CompactionReason reason, int c)
        : stats(reason, c), penultimate_level_stats(reason, c){};

    uint64_t TotalBytesWritten() const {
      uint64_t bytes_written = stats.bytes_written + stats.bytes_written_blob;
      if (has_penultimate_level_output) {
        bytes_written += penultimate_level_stats.bytes_written +
                         penultimate_level_stats.bytes_written_blob;
      }
      return bytes_written;
    }

    uint64_t DroppedRecords() {
      uint64_t output_records = stats.num_output_records;
      if (has_penultimate_level_output) {
        output_records += penultimate_level_stats.num_output_records;
      }
      if (stats.num_input_records > output_records) {
        return stats.num_input_records - output_records;
      }
      return 0;
    }

    void SetMicros(uint64_t val) {
      stats.micros = val;
      penultimate_level_stats.micros = val;
    }

    void AddCpuMicros(uint64_t val) {
      stats.cpu_micros += val;
      penultimate_level_stats.cpu_micros += val;
    }
  };

  // For use with CacheEntryStatsCollector
  struct CacheEntryRoleStats {
    uint64_t cache_capacity = 0;
    std::string cache_id;
    std::array<uint64_t, kNumCacheEntryRoles> total_charges;
    std::array<size_t, kNumCacheEntryRoles> entry_counts;
    uint32_t collection_count = 0;
    uint32_t copies_of_last_collection = 0;
    uint64_t last_start_time_micros_ = 0;
    uint64_t last_end_time_micros_ = 0;

    void Clear() {
      // Wipe everything except collection_count
      uint32_t saved_collection_count = collection_count;
      *this = CacheEntryRoleStats();
      collection_count = saved_collection_count;
    }

    void BeginCollection(Cache*, SystemClock*, uint64_t start_time_micros);
    std::function<void(const Slice&, void*, size_t, Cache::DeleterFn)>
    GetEntryCallback();
    void EndCollection(Cache*, SystemClock*, uint64_t end_time_micros);
    void SkippedCollection();

    std::string ToString(SystemClock* clock) const;
    void ToMap(std::map<std::string, std::string>* values,
               SystemClock* clock) const;

   private:
    UnorderedMap<Cache::DeleterFn, CacheEntryRole> role_map_;
    uint64_t GetLastDurationMicros() const;
  };

  void Clear() {
    for (int i = 0; i < kIntStatsNumMax; i++) {
      db_stats_[i].store(0);
    }
    for (int i = 0; i < INTERNAL_CF_STATS_ENUM_MAX; i++) {
      cf_stats_count_[i] = 0;
      cf_stats_value_[i] = 0;
    }
    for (auto& comp_stat : comp_stats_) {
      comp_stat.Clear();
    }
    per_key_placement_comp_stats_.Clear();
    for (auto& h : file_read_latency_) {
      h.Clear();
    }
    blob_file_read_latency_.Clear();
    cf_stats_snapshot_.Clear();
    db_stats_snapshot_.Clear();
    bg_error_count_ = 0;
    started_at_ = clock_->NowMicros();
  }

  void AddCompactionStats(int level, Env::Priority thread_pri,
                          const CompactionStats& stats) {
    comp_stats_[level].Add(stats);
    comp_stats_by_pri_[thread_pri].Add(stats);
  }

  void AddCompactionStats(int level, Env::Priority thread_pri,
                          const CompactionStatsFull& comp_stats_full) {
    AddCompactionStats(level, thread_pri, comp_stats_full.stats);
    if (comp_stats_full.has_penultimate_level_output) {
      per_key_placement_comp_stats_.Add(
          comp_stats_full.penultimate_level_stats);
    }
  }

  void IncBytesMoved(int level, uint64_t amount) {
    comp_stats_[level].bytes_moved += amount;
  }

  void AddCFStats(InternalCFStatsType type, uint64_t value) {
    cf_stats_value_[type] += value;
    ++cf_stats_count_[type];
  }

  void AddDBStats(InternalDBStatsType type, uint64_t value,
                  bool concurrent = false) {
    auto& v = db_stats_[type];
    if (concurrent) {
      v.fetch_add(value, std::memory_order_relaxed);
    } else {
      v.store(v.load(std::memory_order_relaxed) + value,
              std::memory_order_relaxed);
    }
  }

  uint64_t GetDBStats(InternalDBStatsType type) {
    return db_stats_[type].load(std::memory_order_relaxed);
  }

  HistogramImpl* GetFileReadHist(int level) {
    return &file_read_latency_[level];
  }

  HistogramImpl* GetBlobFileReadHist() { return &blob_file_read_latency_; }

  uint64_t GetBackgroundErrorCount() const { return bg_error_count_; }

  uint64_t BumpAndGetBackgroundErrorCount() { return ++bg_error_count_; }

  bool GetStringProperty(const DBPropertyInfo& property_info,
                         const Slice& property, std::string* value);

  bool GetMapProperty(const DBPropertyInfo& property_info,
                      const Slice& property,
                      std::map<std::string, std::string>* value);

  bool GetIntProperty(const DBPropertyInfo& property_info, uint64_t* value,
                      DBImpl* db);

  bool GetIntPropertyOutOfMutex(const DBPropertyInfo& property_info,
                                Version* version, uint64_t* value);

  // Unless there is a recent enough collection of the stats, collect and
  // saved new cache entry stats. If `foreground`, require data to be more
  // recent to skip re-collection.
  //
  // This should only be called while NOT holding the DB mutex.
  void CollectCacheEntryStats(bool foreground);

  const uint64_t* TEST_GetCFStatsValue() const { return cf_stats_value_; }

  const std::vector<CompactionStats>& TEST_GetCompactionStats() const {
    return comp_stats_;
  }

  const CompactionStats& TEST_GetPerKeyPlacementCompactionStats() const {
    return per_key_placement_comp_stats_;
  }

  void TEST_GetCacheEntryRoleStats(CacheEntryRoleStats* stats, bool foreground);

  // Store a mapping from the user-facing DB::Properties string to our
  // DBPropertyInfo struct used internally for retrieving properties.
  static const UnorderedMap<std::string, DBPropertyInfo> ppt_name_to_info;

 private:
  void DumpDBMapStats(std::map<std::string, std::string>* db_stats);
  void DumpDBStats(std::string* value);
  void DumpCFMapStats(std::map<std::string, std::string>* cf_stats);
  void DumpCFMapStats(
      const VersionStorageInfo* vstorage,
      std::map<int, std::map<LevelStatType, double>>* level_stats,
      CompactionStats* compaction_stats_sum);
  void DumpCFMapStatsByPriority(
      std::map<int, std::map<LevelStatType, double>>* priorities_stats);
  void DumpCFMapStatsIOStalls(std::map<std::string, std::string>* cf_stats);
  void DumpCFStats(std::string* value);
  void DumpCFStatsNoFileHistogram(std::string* value);
  void DumpCFFileHistogram(std::string* value);

  Cache* GetBlockCacheForStats();
  Cache* GetBlobCacheForStats();

  // Per-DB stats
  std::atomic<uint64_t> db_stats_[kIntStatsNumMax];
  // Per-ColumnFamily stats
  uint64_t cf_stats_value_[INTERNAL_CF_STATS_ENUM_MAX];
  uint64_t cf_stats_count_[INTERNAL_CF_STATS_ENUM_MAX];
  // Initialize/reference the collector in constructor so that we don't need
  // additional synchronization in InternalStats, relying on synchronization
  // in CacheEntryStatsCollector::GetStats. This collector is pinned in cache
  // (through a shared_ptr) so that it does not get immediately ejected from
  // a full cache, which would force a re-scan on the next GetStats.
  std::shared_ptr<CacheEntryStatsCollector<CacheEntryRoleStats>>
      cache_entry_stats_collector_;
  // Per-ColumnFamily/level compaction stats
  std::vector<CompactionStats> comp_stats_;
  std::vector<CompactionStats> comp_stats_by_pri_;
  CompactionStats per_key_placement_comp_stats_;
  std::vector<HistogramImpl> file_read_latency_;
  HistogramImpl blob_file_read_latency_;

  // Used to compute per-interval statistics
  struct CFStatsSnapshot {
    // ColumnFamily-level stats
    CompactionStats comp_stats;
    uint64_t ingest_bytes_flush;      // Bytes written to L0 (Flush)
    uint64_t stall_count;             // Stall count
    // Stats from compaction jobs - bytes written, bytes read, duration.
    uint64_t compact_bytes_write;
    uint64_t compact_bytes_read;
    uint64_t compact_micros;
    double seconds_up;

    // AddFile specific stats
    uint64_t ingest_bytes_addfile;     // Total Bytes ingested
    uint64_t ingest_files_addfile;     // Total number of files ingested
    uint64_t ingest_l0_files_addfile;  // Total number of files ingested to L0
    uint64_t ingest_keys_addfile;      // Total number of keys ingested

    CFStatsSnapshot()
        : ingest_bytes_flush(0),
          stall_count(0),
          compact_bytes_write(0),
          compact_bytes_read(0),
          compact_micros(0),
          seconds_up(0),
          ingest_bytes_addfile(0),
          ingest_files_addfile(0),
          ingest_l0_files_addfile(0),
          ingest_keys_addfile(0) {}

    void Clear() {
      comp_stats.Clear();
      ingest_bytes_flush = 0;
      stall_count = 0;
      compact_bytes_write = 0;
      compact_bytes_read = 0;
      compact_micros = 0;
      seconds_up = 0;
      ingest_bytes_addfile = 0;
      ingest_files_addfile = 0;
      ingest_l0_files_addfile = 0;
      ingest_keys_addfile = 0;
    }
  } cf_stats_snapshot_;

  struct DBStatsSnapshot {
    // DB-level stats
    uint64_t ingest_bytes;            // Bytes written by user
    uint64_t wal_bytes;               // Bytes written to WAL
    uint64_t wal_synced;              // Number of times WAL is synced
    uint64_t write_with_wal;          // Number of writes that request WAL
    // These count the number of writes processed by the calling thread or
    // another thread.
    uint64_t write_other;
    uint64_t write_self;
    // Total number of keys written. write_self and write_other measure number
    // of write requests written, Each of the write request can contain updates
    // to multiple keys. num_keys_written is total number of keys updated by all
    // those writes.
    uint64_t num_keys_written;
    // Total time writes delayed by stalls.
    uint64_t write_stall_micros;
    double seconds_up;

    DBStatsSnapshot()
        : ingest_bytes(0),
          wal_bytes(0),
          wal_synced(0),
          write_with_wal(0),
          write_other(0),
          write_self(0),
          num_keys_written(0),
          write_stall_micros(0),
          seconds_up(0) {}

    void Clear() {
      ingest_bytes = 0;
      wal_bytes = 0;
      wal_synced = 0;
      write_with_wal = 0;
      write_other = 0;
      write_self = 0;
      num_keys_written = 0;
      write_stall_micros = 0;
      seconds_up = 0;
    }
  } db_stats_snapshot_;

  // Handler functions for getting property values. They use "value" as a value-
  // result argument, and return true upon successfully setting "value".
  bool HandleNumFilesAtLevel(std::string* value, Slice suffix);
  bool HandleCompressionRatioAtLevelPrefix(std::string* value, Slice suffix);
  bool HandleLevelStats(std::string* value, Slice suffix);
  bool HandleStats(std::string* value, Slice suffix);
  bool HandleCFMapStats(std::map<std::string, std::string>* compaction_stats,
                        Slice suffix);
  bool HandleCFStats(std::string* value, Slice suffix);
  bool HandleCFStatsNoFileHistogram(std::string* value, Slice suffix);
  bool HandleCFFileHistogram(std::string* value, Slice suffix);
  bool HandleDBMapStats(std::map<std::string, std::string>* compaction_stats,
                        Slice suffix);
  bool HandleDBStats(std::string* value, Slice suffix);
  bool HandleSsTables(std::string* value, Slice suffix);
  bool HandleAggregatedTableProperties(std::string* value, Slice suffix);
  bool HandleAggregatedTablePropertiesAtLevel(std::string* value, Slice suffix);
  bool HandleAggregatedTablePropertiesMap(
      std::map<std::string, std::string>* values, Slice suffix);
  bool HandleAggregatedTablePropertiesAtLevelMap(
      std::map<std::string, std::string>* values, Slice suffix);
  bool HandleNumImmutableMemTable(uint64_t* value, DBImpl* db,
                                  Version* version);
  bool HandleNumImmutableMemTableFlushed(uint64_t* value, DBImpl* db,
                                         Version* version);
  bool HandleMemTableFlushPending(uint64_t* value, DBImpl* db,
                                  Version* version);
  bool HandleNumRunningFlushes(uint64_t* value, DBImpl* db, Version* version);
  bool HandleCompactionPending(uint64_t* value, DBImpl* db, Version* version);
  bool HandleNumRunningCompactions(uint64_t* value, DBImpl* db,
                                   Version* version);
  bool HandleBackgroundErrors(uint64_t* value, DBImpl* db, Version* version);
  bool HandleCurSizeActiveMemTable(uint64_t* value, DBImpl* db,
                                   Version* version);
  bool HandleCurSizeAllMemTables(uint64_t* value, DBImpl* db, Version* version);
  bool HandleSizeAllMemTables(uint64_t* value, DBImpl* db, Version* version);
  bool HandleNumEntriesActiveMemTable(uint64_t* value, DBImpl* db,
                                      Version* version);
  bool HandleNumEntriesImmMemTables(uint64_t* value, DBImpl* db,
                                    Version* version);
  bool HandleNumDeletesActiveMemTable(uint64_t* value, DBImpl* db,
                                      Version* version);
  bool HandleNumDeletesImmMemTables(uint64_t* value, DBImpl* db,
                                    Version* version);
  bool HandleEstimateNumKeys(uint64_t* value, DBImpl* db, Version* version);
  bool HandleNumSnapshots(uint64_t* value, DBImpl* db, Version* version);
  bool HandleOldestSnapshotTime(uint64_t* value, DBImpl* db, Version* version);
  bool HandleOldestSnapshotSequence(uint64_t* value, DBImpl* db,
                                    Version* version);
  bool HandleNumLiveVersions(uint64_t* value, DBImpl* db, Version* version);
  bool HandleCurrentSuperVersionNumber(uint64_t* value, DBImpl* db,
                                       Version* version);
  bool HandleIsFileDeletionsEnabled(uint64_t* value, DBImpl* db,
                                    Version* version);
  bool HandleBaseLevel(uint64_t* value, DBImpl* db, Version* version);
  bool HandleTotalSstFilesSize(uint64_t* value, DBImpl* db, Version* version);
  bool HandleLiveSstFilesSize(uint64_t* value, DBImpl* db, Version* version);
  bool HandleEstimatePendingCompactionBytes(uint64_t* value, DBImpl* db,
                                            Version* version);
  bool HandleEstimateTableReadersMem(uint64_t* value, DBImpl* db,
                                     Version* version);
  bool HandleEstimateLiveDataSize(uint64_t* value, DBImpl* db,
                                  Version* version);
  bool HandleMinLogNumberToKeep(uint64_t* value, DBImpl* db, Version* version);
  bool HandleMinObsoleteSstNumberToKeep(uint64_t* value, DBImpl* db,
                                        Version* version);
  bool HandleActualDelayedWriteRate(uint64_t* value, DBImpl* db,
                                    Version* version);
  bool HandleIsWriteStopped(uint64_t* value, DBImpl* db, Version* version);
  bool HandleEstimateOldestKeyTime(uint64_t* value, DBImpl* db,
                                   Version* version);
  bool HandleBlockCacheCapacity(uint64_t* value, DBImpl* db, Version* version);
  bool HandleBlockCacheUsage(uint64_t* value, DBImpl* db, Version* version);
  bool HandleBlockCachePinnedUsage(uint64_t* value, DBImpl* db,
                                   Version* version);
  bool HandleBlockCacheEntryStats(std::string* value, Slice suffix);
  bool HandleBlockCacheEntryStatsMap(std::map<std::string, std::string>* values,
                                     Slice suffix);
  bool HandleLiveSstFilesSizeAtTemperature(std::string* value, Slice suffix);
  bool HandleNumBlobFiles(uint64_t* value, DBImpl* db, Version* version);
  bool HandleBlobStats(std::string* value, Slice suffix);
  bool HandleTotalBlobFileSize(uint64_t* value, DBImpl* db, Version* version);
  bool HandleLiveBlobFileSize(uint64_t* value, DBImpl* db, Version* version);
  bool HandleLiveBlobFileGarbageSize(uint64_t* value, DBImpl* db,
                                     Version* version);
  bool HandleBlobCacheCapacity(uint64_t* value, DBImpl* db, Version* version);
  bool HandleBlobCacheUsage(uint64_t* value, DBImpl* db, Version* version);
  bool HandleBlobCachePinnedUsage(uint64_t* value, DBImpl* db,
                                  Version* version);

  // Total number of background errors encountered. Every time a flush task
  // or compaction task fails, this counter is incremented. The failure can
  // be caused by any possible reason, including file system errors, out of
  // resources, or input file corruption. Failing when retrying the same flush
  // or compaction will cause the counter to increase too.
  uint64_t bg_error_count_;

  const int number_levels_;
  SystemClock* clock_;
  ColumnFamilyData* cfd_;
  uint64_t started_at_;
};

#else

class InternalStats {
 public:
  enum InternalCFStatsType {
    L0_FILE_COUNT_LIMIT_SLOWDOWNS,
    LOCKED_L0_FILE_COUNT_LIMIT_SLOWDOWNS,
    MEMTABLE_LIMIT_STOPS,
    MEMTABLE_LIMIT_SLOWDOWNS,
    L0_FILE_COUNT_LIMIT_STOPS,
    LOCKED_L0_FILE_COUNT_LIMIT_STOPS,
    PENDING_COMPACTION_BYTES_LIMIT_SLOWDOWNS,
    PENDING_COMPACTION_BYTES_LIMIT_STOPS,
    WRITE_STALLS_ENUM_MAX,
    BYTES_FLUSHED,
    BYTES_INGESTED_ADD_FILE,
    INGESTED_NUM_FILES_TOTAL,
    INGESTED_LEVEL0_NUM_FILES_TOTAL,
    INGESTED_NUM_KEYS_TOTAL,
    INTERNAL_CF_STATS_ENUM_MAX,
  };

  enum InternalDBStatsType {
    kIntStatsWalFileBytes,
    kIntStatsWalFileSynced,
    kIntStatsBytesWritten,
    kIntStatsNumKeysWritten,
    kIntStatsWriteDoneByOther,
    kIntStatsWriteDoneBySelf,
    kIntStatsWriteWithWal,
    kIntStatsWriteStallMicros,
    kIntStatsNumMax,
  };

  InternalStats(int /*num_levels*/, SystemClock* /*clock*/,
                ColumnFamilyData* /*cfd*/) {}

  // Per level compaction stats
  struct CompactionOutputsStats {
    uint64_t num_output_records = 0;
    uint64_t bytes_written = 0;
    uint64_t bytes_written_blob = 0;
    uint64_t num_output_files = 0;
    uint64_t num_output_files_blob = 0;

    void Add(const CompactionOutputsStats& stats) {
      this->num_output_records += stats.num_output_records;
      this->bytes_written += stats.bytes_written;
      this->bytes_written_blob += stats.bytes_written_blob;
      this->num_output_files += stats.num_output_files;
      this->num_output_files_blob += stats.num_output_files_blob;
    }
  };

  struct CompactionStats {
    uint64_t micros;
    uint64_t cpu_micros;
    uint64_t bytes_read_non_output_levels;
    uint64_t bytes_read_output_level;
    uint64_t bytes_read_blob;
    uint64_t bytes_written;
    uint64_t bytes_written_blob;
    uint64_t bytes_moved;
    int num_input_files_in_non_output_levels;
    int num_input_files_in_output_level;
    int num_output_files;
    int num_output_files_blob;
    uint64_t num_input_records;
    uint64_t num_dropped_records;
    uint64_t num_output_records;
    int count;

    explicit CompactionStats() {}

    explicit CompactionStats(CompactionReason /*reason*/, int /*c*/) {}

    explicit CompactionStats(const CompactionStats& /*c*/) {}

    void Add(const CompactionStats& /*c*/) {}

    void Add(const CompactionOutputsStats& /*c*/) {}

    void Subtract(const CompactionStats& /*c*/) {}
  };

  struct CompactionStatsFull {
    // the stats for the target primary output level (per level stats)
    CompactionStats stats;

    // stats for output_to_penultimate_level level (per level stats)
    bool has_penultimate_level_output = false;
    CompactionStats penultimate_level_stats;

    explicit CompactionStatsFull(){};

    explicit CompactionStatsFull(CompactionReason /*reason*/, int /*c*/){};

    uint64_t TotalBytesWritten() const { return 0; }

    uint64_t DroppedRecords() { return 0; }

    void SetMicros(uint64_t /*val*/){};

    void AddCpuMicros(uint64_t /*val*/){};
  };

  void AddCompactionStats(int /*level*/, Env::Priority /*thread_pri*/,
                          const CompactionStats& /*stats*/) {}

  void AddCompactionStats(int /*level*/, Env::Priority /*thread_pri*/,
                          const CompactionStatsFull& /*unmerged_stats*/) {}

  void IncBytesMoved(int /*level*/, uint64_t /*amount*/) {}

  void AddCFStats(InternalCFStatsType /*type*/, uint64_t /*value*/) {}

  void AddDBStats(InternalDBStatsType /*type*/, uint64_t /*value*/,
                  bool /*concurrent */ = false) {}

  HistogramImpl* GetFileReadHist(int /*level*/) { return nullptr; }

  HistogramImpl* GetBlobFileReadHist() { return nullptr; }

  uint64_t GetBackgroundErrorCount() const { return 0; }

  uint64_t BumpAndGetBackgroundErrorCount() { return 0; }

  bool GetStringProperty(const DBPropertyInfo& /*property_info*/,
                         const Slice& /*property*/, std::string* /*value*/) {
    return false;
  }

  bool GetMapProperty(const DBPropertyInfo& /*property_info*/,
                      const Slice& /*property*/,
                      std::map<std::string, std::string>* /*value*/) {
    return false;
  }

  bool GetIntProperty(const DBPropertyInfo& /*property_info*/, uint64_t* /*value*/,
                      DBImpl* /*db*/) const {
    return false;
  }

  bool GetIntPropertyOutOfMutex(const DBPropertyInfo& /*property_info*/,
                                Version* /*version*/, uint64_t* /*value*/) const {
    return false;
  }
};
#endif  // !ROCKSDB_LITE

}  // namespace ROCKSDB_NAMESPACE