db_impl.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.
//  This source code is also licensed under the GPLv2 license found in the
//  COPYING file in the root directory of this source tree.
//
// 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_impl.h"

#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include <inttypes.h>
#include <stdint.h>
#ifdef OS_SOLARIS
#include <alloca.h>
#endif
#ifdef ROCKSDB_JEMALLOC
#include "jemalloc/jemalloc.h"
#endif

#include <algorithm>
#include <climits>
#include <cstdio>
#include <map>
#include <set>
#include <stdexcept>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#include "db/builder.h"
#include "db/compaction_job.h"
#include "db/db_info_dumper.h"
#include "db/db_iter.h"
#include "db/dbformat.h"
#include "db/event_helpers.h"
#include "db/external_sst_file_ingestion_job.h"
#include "db/flush_job.h"
#include "db/forward_iterator.h"
#include "db/job_context.h"
#include "db/log_reader.h"
#include "db/log_writer.h"
#include "db/managed_iterator.h"
#include "db/memtable.h"
#include "db/memtable_list.h"
#include "db/merge_context.h"
#include "db/merge_helper.h"
#include "db/range_del_aggregator.h"
#include "db/table_cache.h"
#include "db/table_properties_collector.h"
#include "db/transaction_log_impl.h"
#include "db/version_set.h"
#include "db/write_batch_internal.h"
#include "db/write_callback.h"
#include "memtable/hash_linklist_rep.h"
#include "memtable/hash_skiplist_rep.h"
#include "monitoring/iostats_context_imp.h"
#include "monitoring/perf_context_imp.h"
#include "monitoring/thread_status_updater.h"
#include "monitoring/thread_status_util.h"
#include "options/cf_options.h"
#include "options/options_helper.h"
#include "options/options_parser.h"
#include "port/likely.h"
#include "port/port.h"
#include "rocksdb/cache.h"
#include "rocksdb/compaction_filter.h"
#include "rocksdb/db.h"
#include "rocksdb/env.h"
#include "rocksdb/merge_operator.h"
#include "rocksdb/statistics.h"
#include "rocksdb/status.h"
#include "rocksdb/table.h"
#include "rocksdb/version.h"
#include "rocksdb/write_buffer_manager.h"
#include "table/block.h"
#include "table/block_based_table_factory.h"
#include "table/merging_iterator.h"
#include "table/table_builder.h"
#include "table/two_level_iterator.h"
#include "util/auto_roll_logger.h"
#include "util/autovector.h"
#include "util/build_version.h"
#include "util/coding.h"
#include "util/compression.h"
#include "util/crc32c.h"
#include "util/file_reader_writer.h"
#include "util/file_util.h"
#include "util/filename.h"
#include "util/log_buffer.h"
#include "util/logging.h"
#include "util/mutexlock.h"
#include "util/sst_file_manager_impl.h"
#include "util/stop_watch.h"
#include "util/string_util.h"
#include "util/sync_point.h"

namespace rocksdb {
const std::string kDefaultColumnFamilyName("default");
void DumpRocksDBBuildVersion(Logger * log);

CompressionType GetCompressionFlush(
    const ImmutableCFOptions& ioptions,
    const MutableCFOptions& mutable_cf_options) {
  // Compressing memtable flushes might not help unless the sequential load
  // optimization is used for leveled compaction. Otherwise the CPU and
  // latency overhead is not offset by saving much space.
  if (ioptions.compaction_style == kCompactionStyleUniversal) {
    if (ioptions.compaction_options_universal.compression_size_percent < 0) {
      return mutable_cf_options.compression;
    } else {
      return kNoCompression;
    }
  } else if (!ioptions.compression_per_level.empty()) {
    // For leveled compress when min_level_to_compress != 0.
    return ioptions.compression_per_level[0];
  } else {
    return mutable_cf_options.compression;
  }
}

namespace {
void DumpSupportInfo(Logger* logger) {
  ROCKS_LOG_HEADER(logger, "Compression algorithms supported:");
  ROCKS_LOG_HEADER(logger, "\tSnappy supported: %d", Snappy_Supported());
  ROCKS_LOG_HEADER(logger, "\tZlib supported: %d", Zlib_Supported());
  ROCKS_LOG_HEADER(logger, "\tBzip supported: %d", BZip2_Supported());
  ROCKS_LOG_HEADER(logger, "\tLZ4 supported: %d", LZ4_Supported());
  ROCKS_LOG_HEADER(logger, "\tZSTD supported: %d", ZSTD_Supported());
  ROCKS_LOG_HEADER(logger, "Fast CRC32 supported: %d",
                   crc32c::IsFastCrc32Supported());
}
} // namespace

DBImpl::DBImpl(const DBOptions& options, const std::string& dbname)
    : env_(options.env),
      dbname_(dbname),
      initial_db_options_(SanitizeOptions(dbname, options)),
      immutable_db_options_(initial_db_options_),
      mutable_db_options_(initial_db_options_),
      stats_(immutable_db_options_.statistics.get()),
      db_lock_(nullptr),
      mutex_(stats_, env_, DB_MUTEX_WAIT_MICROS,
             immutable_db_options_.use_adaptive_mutex),
      shutting_down_(false),
      bg_cv_(&mutex_),
      logfile_number_(0),
      log_dir_synced_(false),
      log_empty_(true),
      default_cf_handle_(nullptr),
      log_sync_cv_(&mutex_),
      total_log_size_(0),
      max_total_in_memory_state_(0),
      is_snapshot_supported_(true),
      write_buffer_manager_(immutable_db_options_.write_buffer_manager.get()),
      write_thread_(immutable_db_options_.enable_write_thread_adaptive_yield
                        ? immutable_db_options_.write_thread_max_yield_usec
                        : 0,
                    immutable_db_options_.write_thread_slow_yield_usec),
      write_controller_(mutable_db_options_.delayed_write_rate),
      last_batch_group_size_(0),
      unscheduled_flushes_(0),
      unscheduled_compactions_(0),
      bg_compaction_scheduled_(0),
      num_running_compactions_(0),
      bg_flush_scheduled_(0),
      num_running_flushes_(0),
      bg_purge_scheduled_(0),
      disable_delete_obsolete_files_(0),
      delete_obsolete_files_last_run_(env_->NowMicros()),
      last_stats_dump_time_microsec_(0),
      next_job_id_(1),
      has_unpersisted_data_(false),
      unable_to_flush_oldest_log_(false),
      env_options_(BuildDBOptions(immutable_db_options_, mutable_db_options_)),
      num_running_ingest_file_(0),
#ifndef ROCKSDB_LITE
      wal_manager_(immutable_db_options_, env_options_),
#endif  // ROCKSDB_LITE
      event_logger_(immutable_db_options_.info_log.get()),
      bg_work_paused_(0),
      bg_compaction_paused_(0),
      refitting_level_(false),
      opened_successfully_(false) {
  env_->GetAbsolutePath(dbname, &db_absolute_path_);

  // Reserve ten files or so for other uses and give the rest to TableCache.
  // Give a large number for setting of "infinite" open files.
  const int table_cache_size = (mutable_db_options_.max_open_files == -1)
                                   ? 0x400000
                                   : mutable_db_options_.max_open_files - 10;
  table_cache_ = NewLRUCache(table_cache_size,
                             immutable_db_options_.table_cache_numshardbits);

  versions_.reset(new VersionSet(dbname_, &immutable_db_options_, env_options_,
                                 table_cache_.get(), write_buffer_manager_,
                                 &write_controller_));
  column_family_memtables_.reset(
      new ColumnFamilyMemTablesImpl(versions_->GetColumnFamilySet()));

  DumpRocksDBBuildVersion(immutable_db_options_.info_log.get());
  DumpDBFileSummary(immutable_db_options_, dbname_);
  immutable_db_options_.Dump(immutable_db_options_.info_log.get());
  mutable_db_options_.Dump(immutable_db_options_.info_log.get());
  DumpSupportInfo(immutable_db_options_.info_log.get());
}

// Will lock the mutex_,  will wait for completion if wait is true
void DBImpl::CancelAllBackgroundWork(bool wait) {
  InstrumentedMutexLock l(&mutex_);

  ROCKS_LOG_INFO(immutable_db_options_.info_log,
                 "Shutdown: canceling all background work");

  if (!shutting_down_.load(std::memory_order_acquire) &&
      has_unpersisted_data_.load(std::memory_order_relaxed) &&
      !mutable_db_options_.avoid_flush_during_shutdown) {
    for (auto cfd : *versions_->GetColumnFamilySet()) {
      if (!cfd->IsDropped() && !cfd->mem()->IsEmpty()) {
        cfd->Ref();
        mutex_.Unlock();
        FlushMemTable(cfd, FlushOptions());
        mutex_.Lock();
        cfd->Unref();
      }
    }
    versions_->GetColumnFamilySet()->FreeDeadColumnFamilies();
  }

  shutting_down_.store(true, std::memory_order_release);
  bg_cv_.SignalAll();
  if (!wait) {
    return;
  }
  // Wait for background work to finish
  while (bg_compaction_scheduled_ || bg_flush_scheduled_) {
    bg_cv_.Wait();
  }
}

DBImpl::~DBImpl() {
  // CancelAllBackgroundWork called with false means we just set the shutdown
  // marker. After this we do a variant of the waiting and unschedule work
  // (to consider: moving all the waiting into CancelAllBackgroundWork(true))
  CancelAllBackgroundWork(false);
  int compactions_unscheduled = env_->UnSchedule(this, Env::Priority::LOW);
  int flushes_unscheduled = env_->UnSchedule(this, Env::Priority::HIGH);
  mutex_.Lock();
  bg_compaction_scheduled_ -= compactions_unscheduled;
  bg_flush_scheduled_ -= flushes_unscheduled;

  // Wait for background work to finish
  while (bg_compaction_scheduled_ || bg_flush_scheduled_ ||
         bg_purge_scheduled_) {
    TEST_SYNC_POINT("DBImpl::~DBImpl:WaitJob");
    bg_cv_.Wait();
  }
  EraseThreadStatusDbInfo();
  flush_scheduler_.Clear();

  while (!flush_queue_.empty()) {
    auto cfd = PopFirstFromFlushQueue();
    if (cfd->Unref()) {
      delete cfd;
    }
  }
  while (!compaction_queue_.empty()) {
    auto cfd = PopFirstFromCompactionQueue();
    if (cfd->Unref()) {
      delete cfd;
    }
  }

  if (default_cf_handle_ != nullptr) {
    // we need to delete handle outside of lock because it does its own locking
    mutex_.Unlock();
    delete default_cf_handle_;
    mutex_.Lock();
  }

  // Clean up obsolete files due to SuperVersion release.
  // (1) Need to delete to obsolete files before closing because RepairDB()
  // scans all existing files in the file system and builds manifest file.
  // Keeping obsolete files confuses the repair process.
  // (2) Need to check if we Open()/Recover() the DB successfully before
  // deleting because if VersionSet recover fails (may be due to corrupted
  // manifest file), it is not able to identify live files correctly. As a
  // result, all "live" files can get deleted by accident. However, corrupted
  // manifest is recoverable by RepairDB().
  if (opened_successfully_) {
    JobContext job_context(next_job_id_.fetch_add(1));
    FindObsoleteFiles(&job_context, true);

    mutex_.Unlock();
    // manifest number starting from 2
    job_context.manifest_file_number = 1;
    if (job_context.HaveSomethingToDelete()) {
      PurgeObsoleteFiles(job_context);
    }
    job_context.Clean();
    mutex_.Lock();
  }

  for (auto l : logs_to_free_) {
    delete l;
  }
  for (auto& log : logs_) {
    log.ClearWriter();
  }
  logs_.clear();

  // Table cache may have table handles holding blocks from the block cache.
  // We need to release them before the block cache is destroyed. The block
  // cache may be destroyed inside versions_.reset(), when column family data
  // list is destroyed, so leaving handles in table cache after
  // versions_.reset() may cause issues.
  // Here we clean all unreferenced handles in table cache.
  // Now we assume all user queries have finished, so only version set itself
  // can possibly hold the blocks from block cache. After releasing unreferenced
  // handles here, only handles held by version set left and inside
  // versions_.reset(), we will release them. There, we need to make sure every
  // time a handle is released, we erase it from the cache too. By doing that,
  // we can guarantee that after versions_.reset(), table cache is empty
  // so the cache can be safely destroyed.
  table_cache_->EraseUnRefEntries();

  for (auto& txn_entry : recovered_transactions_) {
    delete txn_entry.second;
  }

  // versions need to be destroyed before table_cache since it can hold
  // references to table_cache.
  versions_.reset();
  mutex_.Unlock();
  if (db_lock_ != nullptr) {
    env_->UnlockFile(db_lock_);
  }

  ROCKS_LOG_INFO(immutable_db_options_.info_log, "Shutdown complete");
  LogFlush(immutable_db_options_.info_log);
}

void DBImpl::MaybeIgnoreError(Status* s) const {
  if (s->ok() || immutable_db_options_.paranoid_checks) {
    // No change needed
  } else {
    ROCKS_LOG_WARN(immutable_db_options_.info_log, "Ignoring error %s",
                   s->ToString().c_str());
    *s = Status::OK();
  }
}

const Status DBImpl::CreateArchivalDirectory() {
  if (immutable_db_options_.wal_ttl_seconds > 0 ||
      immutable_db_options_.wal_size_limit_mb > 0) {
    std::string archivalPath = ArchivalDirectory(immutable_db_options_.wal_dir);
    return env_->CreateDirIfMissing(archivalPath);
  }
  return Status::OK();
}

void DBImpl::PrintStatistics() {
  auto dbstats = immutable_db_options_.statistics.get();
  if (dbstats) {
    ROCKS_LOG_WARN(immutable_db_options_.info_log, "STATISTICS:\n %s",
                   dbstats->ToString().c_str());
  }
}

#ifndef ROCKSDB_LITE
#ifdef ROCKSDB_JEMALLOC
typedef struct {
  char* cur;
  char* end;
} MallocStatus;

static void GetJemallocStatus(void* mstat_arg, const char* status) {
  MallocStatus* mstat = reinterpret_cast<MallocStatus*>(mstat_arg);
  size_t status_len = status ? strlen(status) : 0;
  size_t buf_size = (size_t)(mstat->end - mstat->cur);
  if (!status_len || status_len > buf_size) {
    return;
  }

  snprintf(mstat->cur, buf_size, "%s", status);
  mstat->cur += status_len;
}
#endif  // ROCKSDB_JEMALLOC

static void DumpMallocStats(std::string* stats) {
#ifdef ROCKSDB_JEMALLOC
  MallocStatus mstat;
  const unsigned int kMallocStatusLen = 1000000;
  std::unique_ptr<char[]> buf{new char[kMallocStatusLen + 1]};
  mstat.cur = buf.get();
  mstat.end = buf.get() + kMallocStatusLen;
  je_malloc_stats_print(GetJemallocStatus, &mstat, "");
  stats->append(buf.get());
#endif  // ROCKSDB_JEMALLOC
}
#endif  // !ROCKSDB_LITE

void DBImpl::MaybeDumpStats() {
  mutex_.Lock();
  unsigned int stats_dump_period_sec =
      mutable_db_options_.stats_dump_period_sec;
  mutex_.Unlock();
  if (stats_dump_period_sec == 0) return;

  const uint64_t now_micros = env_->NowMicros();

  if (last_stats_dump_time_microsec_ + stats_dump_period_sec * 1000000 <=
      now_micros) {
    // Multiple threads could race in here simultaneously.
    // However, the last one will update last_stats_dump_time_microsec_
    // atomically. We could see more than one dump during one dump
    // period in rare cases.
    last_stats_dump_time_microsec_ = now_micros;

#ifndef ROCKSDB_LITE
    const DBPropertyInfo* cf_property_info =
        GetPropertyInfo(DB::Properties::kCFStats);
    assert(cf_property_info != nullptr);
    const DBPropertyInfo* db_property_info =
        GetPropertyInfo(DB::Properties::kDBStats);
    assert(db_property_info != nullptr);

    std::string stats;
    {
      InstrumentedMutexLock l(&mutex_);
      default_cf_internal_stats_->GetStringProperty(
          *db_property_info, DB::Properties::kDBStats, &stats);
      for (auto cfd : *versions_->GetColumnFamilySet()) {
        cfd->internal_stats()->GetStringProperty(
            *cf_property_info, DB::Properties::kCFStatsNoFileHistogram, &stats);
      }
      for (auto cfd : *versions_->GetColumnFamilySet()) {
        cfd->internal_stats()->GetStringProperty(
            *cf_property_info, DB::Properties::kCFFileHistogram, &stats);
      }
    }
    ROCKS_LOG_WARN(immutable_db_options_.info_log,
                   "------- DUMPING STATS -------");
    ROCKS_LOG_WARN(immutable_db_options_.info_log, "%s", stats.c_str());
    if (immutable_db_options_.dump_malloc_stats) {
      stats.clear();
      DumpMallocStats(&stats);
      if (!stats.empty()) {
        ROCKS_LOG_WARN(immutable_db_options_.info_log,
                       "------- Malloc STATS -------");
        ROCKS_LOG_WARN(immutable_db_options_.info_log, "%s", stats.c_str());
      }
    }
#endif  // !ROCKSDB_LITE

    PrintStatistics();
  }
}

void DBImpl::ScheduleBgLogWriterClose(JobContext* job_context) {
  if (!job_context->logs_to_free.empty()) {
    for (auto l : job_context->logs_to_free) {
      AddToLogsToFreeQueue(l);
    }
    job_context->logs_to_free.clear();
    SchedulePurge();
  }
}

Directory* DBImpl::Directories::GetDataDir(size_t path_id) {
  assert(path_id < data_dirs_.size());
  Directory* ret_dir = data_dirs_[path_id].get();
  if (ret_dir == nullptr) {
    // Should use db_dir_
    return db_dir_.get();
  }
  return ret_dir;
}

Status DBImpl::SetOptions(ColumnFamilyHandle* column_family,
    const std::unordered_map<std::string, std::string>& options_map) {
#ifdef ROCKSDB_LITE
  return Status::NotSupported("Not supported in ROCKSDB LITE");
#else
  auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
  if (options_map.empty()) {
    ROCKS_LOG_WARN(immutable_db_options_.info_log,
                   "SetOptions() on column family [%s], empty input",
                   cfd->GetName().c_str());
    return Status::InvalidArgument("empty input");
  }

  MutableCFOptions new_options;
  Status s;
  Status persist_options_status;
  WriteThread::Writer w;
  {
    InstrumentedMutexLock l(&mutex_);
    s = cfd->SetOptions(options_map);
    if (s.ok()) {
      new_options = *cfd->GetLatestMutableCFOptions();
      // Append new version to recompute compaction score.
      VersionEdit dummy_edit;
      versions_->LogAndApply(cfd, new_options, &dummy_edit, &mutex_,
                             directories_.GetDbDir());
      // Trigger possible flush/compactions. This has to be before we persist
      // options to file, otherwise there will be a deadlock with writer
      // thread.
      auto* old_sv =
          InstallSuperVersionAndScheduleWork(cfd, nullptr, new_options);
      delete old_sv;

      write_thread_.EnterUnbatched(&w, &mutex_);
      persist_options_status = WriteOptionsFile();
      write_thread_.ExitUnbatched(&w);
    }
  }

  ROCKS_LOG_INFO(immutable_db_options_.info_log,
                 "SetOptions() on column family [%s], inputs:",
                 cfd->GetName().c_str());
  for (const auto& o : options_map) {
    ROCKS_LOG_INFO(immutable_db_options_.info_log, "%s: %s\n", o.first.c_str(),
                   o.second.c_str());
  }
  if (s.ok()) {
    ROCKS_LOG_INFO(immutable_db_options_.info_log,
                   "[%s] SetOptions() succeeded", cfd->GetName().c_str());
    new_options.Dump(immutable_db_options_.info_log.get());
    if (!persist_options_status.ok()) {
      if (immutable_db_options_.fail_if_options_file_error) {
        s = Status::IOError(
            "SetOptions() succeeded, but unable to persist options",
            persist_options_status.ToString());
      }
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "Unable to persist options in SetOptions() -- %s",
                     persist_options_status.ToString().c_str());
    }
  } else {
    ROCKS_LOG_WARN(immutable_db_options_.info_log, "[%s] SetOptions() failed",
                   cfd->GetName().c_str());
  }
  LogFlush(immutable_db_options_.info_log);
  return s;
#endif  // ROCKSDB_LITE
}

Status DBImpl::SetDBOptions(
    const std::unordered_map<std::string, std::string>& options_map) {
#ifdef ROCKSDB_LITE
  return Status::NotSupported("Not supported in ROCKSDB LITE");
#else
  if (options_map.empty()) {
    ROCKS_LOG_WARN(immutable_db_options_.info_log,
                   "SetDBOptions(), empty input.");
    return Status::InvalidArgument("empty input");
  }

  MutableDBOptions new_options;
  Status s;
  Status persist_options_status;
  WriteThread::Writer w;
  WriteContext write_context;
  {
    InstrumentedMutexLock l(&mutex_);
    s = GetMutableDBOptionsFromStrings(mutable_db_options_, options_map,
                                       &new_options);
    if (s.ok()) {
      if (new_options.max_background_compactions >
          mutable_db_options_.max_background_compactions) {
        env_->IncBackgroundThreadsIfNeeded(
            new_options.max_background_compactions, Env::Priority::LOW);
        MaybeScheduleFlushOrCompaction();
      }

      write_controller_.set_max_delayed_write_rate(new_options.delayed_write_rate);
      table_cache_.get()->SetCapacity(new_options.max_open_files == -1
                                          ? 0x400000
                                          : new_options.max_open_files - 10);

      mutable_db_options_ = new_options;

      write_thread_.EnterUnbatched(&w, &mutex_);
      if (total_log_size_ > GetMaxTotalWalSize()) {
        Status purge_wal_status = HandleWALFull(&write_context);
        if (!purge_wal_status.ok()) {
          ROCKS_LOG_WARN(immutable_db_options_.info_log,
                         "Unable to purge WAL files in SetDBOptions() -- %s",
                         purge_wal_status.ToString().c_str());
        }
      }
      persist_options_status = WriteOptionsFile();
      write_thread_.ExitUnbatched(&w);
    }
  }
  ROCKS_LOG_INFO(immutable_db_options_.info_log, "SetDBOptions(), inputs:");
  for (const auto& o : options_map) {
    ROCKS_LOG_INFO(immutable_db_options_.info_log, "%s: %s\n", o.first.c_str(),
                   o.second.c_str());
  }
  if (s.ok()) {
    ROCKS_LOG_INFO(immutable_db_options_.info_log, "SetDBOptions() succeeded");
    new_options.Dump(immutable_db_options_.info_log.get());
    if (!persist_options_status.ok()) {
      if (immutable_db_options_.fail_if_options_file_error) {
        s = Status::IOError(
            "SetDBOptions() succeeded, but unable to persist options",
            persist_options_status.ToString());
      }
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "Unable to persist options in SetDBOptions() -- %s",
                     persist_options_status.ToString().c_str());
    }
  } else {
    ROCKS_LOG_WARN(immutable_db_options_.info_log, "SetDBOptions failed");
  }
  LogFlush(immutable_db_options_.info_log);
  return s;
#endif  // ROCKSDB_LITE
}

// return the same level if it cannot be moved
int DBImpl::FindMinimumEmptyLevelFitting(ColumnFamilyData* cfd,
    const MutableCFOptions& mutable_cf_options, int level) {
  mutex_.AssertHeld();
  const auto* vstorage = cfd->current()->storage_info();
  int minimum_level = level;
  for (int i = level - 1; i > 0; --i) {
    // stop if level i is not empty
    if (vstorage->NumLevelFiles(i) > 0) break;
    // stop if level i is too small (cannot fit the level files)
    if (vstorage->MaxBytesForLevel(i) < vstorage->NumLevelBytes(level)) {
      break;
    }

    minimum_level = i;
  }
  return minimum_level;
}

Status DBImpl::SyncWAL() {
  autovector<log::Writer*, 1> logs_to_sync;
  bool need_log_dir_sync;
  uint64_t current_log_number;

  {
    InstrumentedMutexLock l(&mutex_);
    assert(!logs_.empty());

    // This SyncWAL() call only cares about logs up to this number.
    current_log_number = logfile_number_;

    while (logs_.front().number <= current_log_number &&
           logs_.front().getting_synced) {
      log_sync_cv_.Wait();
    }
    // First check that logs are safe to sync in background.
    for (auto it = logs_.begin();
         it != logs_.end() && it->number <= current_log_number; ++it) {
      if (!it->writer->file()->writable_file()->IsSyncThreadSafe()) {
        return Status::NotSupported(
            "SyncWAL() is not supported for this implementation of WAL file",
            immutable_db_options_.allow_mmap_writes
                ? "try setting Options::allow_mmap_writes to false"
                : Slice());
      }
    }
    for (auto it = logs_.begin();
         it != logs_.end() && it->number <= current_log_number; ++it) {
      auto& log = *it;
      assert(!log.getting_synced);
      log.getting_synced = true;
      logs_to_sync.push_back(log.writer);
    }

    need_log_dir_sync = !log_dir_synced_;
  }

  RecordTick(stats_, WAL_FILE_SYNCED);
  Status status;
  for (log::Writer* log : logs_to_sync) {
    status = log->file()->SyncWithoutFlush(immutable_db_options_.use_fsync);
    if (!status.ok()) {
      break;
    }
  }
  if (status.ok() && need_log_dir_sync) {
    status = directories_.GetWalDir()->Fsync();
  }

  TEST_SYNC_POINT("DBImpl::SyncWAL:BeforeMarkLogsSynced:1");
  {
    InstrumentedMutexLock l(&mutex_);
    MarkLogsSynced(current_log_number, need_log_dir_sync, status);
  }
  TEST_SYNC_POINT("DBImpl::SyncWAL:BeforeMarkLogsSynced:2");

  return status;
}

void DBImpl::MarkLogsSynced(
    uint64_t up_to, bool synced_dir, const Status& status) {
  mutex_.AssertHeld();
  if (synced_dir &&
      logfile_number_ == up_to &&
      status.ok()) {
    log_dir_synced_ = true;
  }
  for (auto it = logs_.begin(); it != logs_.end() && it->number <= up_to;) {
    auto& log = *it;
    assert(log.getting_synced);
    if (status.ok() && logs_.size() > 1) {
      logs_to_free_.push_back(log.ReleaseWriter());
      it = logs_.erase(it);
    } else {
      log.getting_synced = false;
      ++it;
    }
  }
  assert(!status.ok() || logs_.empty() || logs_[0].number > up_to ||
         (logs_.size() == 1 && !logs_[0].getting_synced));
  log_sync_cv_.SignalAll();
}

SequenceNumber DBImpl::GetLatestSequenceNumber() const {
  return versions_->LastSequence();
}

InternalIterator* DBImpl::NewInternalIterator(
    Arena* arena, RangeDelAggregator* range_del_agg,
    ColumnFamilyHandle* column_family) {
  ColumnFamilyData* cfd;
  if (column_family == nullptr) {
    cfd = default_cf_handle_->cfd();
  } else {
    auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
    cfd = cfh->cfd();
  }

  mutex_.Lock();
  SuperVersion* super_version = cfd->GetSuperVersion()->Ref();
  mutex_.Unlock();
  ReadOptions roptions;
  return NewInternalIterator(roptions, cfd, super_version, arena,
                             range_del_agg);
}

void DBImpl::SchedulePurge() {
  mutex_.AssertHeld();
  assert(opened_successfully_);

  // Purge operations are put into High priority queue
  bg_purge_scheduled_++;
  env_->Schedule(&DBImpl::BGWorkPurge, this, Env::Priority::HIGH, nullptr);
}

void DBImpl::BackgroundCallPurge() {
  mutex_.Lock();

  // We use one single loop to clear both queues so that after existing the loop
  // both queues are empty. This is stricter than what is needed, but can make
  // it easier for us to reason the correctness.
  while (!purge_queue_.empty() || !logs_to_free_queue_.empty()) {
    if (!purge_queue_.empty()) {
      auto purge_file = purge_queue_.begin();
      auto fname = purge_file->fname;
      auto type = purge_file->type;
      auto number = purge_file->number;
      auto path_id = purge_file->path_id;
      auto job_id = purge_file->job_id;
      purge_queue_.pop_front();

      mutex_.Unlock();
      Status file_deletion_status;
      DeleteObsoleteFileImpl(file_deletion_status, job_id, fname, type, number,
                             path_id);
      mutex_.Lock();
    } else {
      assert(!logs_to_free_queue_.empty());
      log::Writer* log_writer = *(logs_to_free_queue_.begin());
      logs_to_free_queue_.pop_front();
      mutex_.Unlock();
      delete log_writer;
      mutex_.Lock();
    }
  }
  bg_purge_scheduled_--;

  bg_cv_.SignalAll();
  // IMPORTANT:there should be no code after calling SignalAll. This call may
  // signal the DB destructor that it's OK to proceed with destruction. In
  // that case, all DB variables will be dealloacated and referencing them
  // will cause trouble.
  mutex_.Unlock();
}

namespace {
struct IterState {
  IterState(DBImpl* _db, InstrumentedMutex* _mu, SuperVersion* _super_version,
            bool _background_purge)
      : db(_db),
        mu(_mu),
        super_version(_super_version),
        background_purge(_background_purge) {}

  DBImpl* db;
  InstrumentedMutex* mu;
  SuperVersion* super_version;
  bool background_purge;
};

static void CleanupIteratorState(void* arg1, void* arg2) {
  IterState* state = reinterpret_cast<IterState*>(arg1);

  if (state->super_version->Unref()) {
    // Job id == 0 means that this is not our background process, but rather
    // user thread
    JobContext job_context(0);

    state->mu->Lock();
    state->super_version->Cleanup();
    state->db->FindObsoleteFiles(&job_context, false, true);
    if (state->background_purge) {
      state->db->ScheduleBgLogWriterClose(&job_context);
    }
    state->mu->Unlock();

    delete state->super_version;
    if (job_context.HaveSomethingToDelete()) {
      if (state->background_purge) {
        // PurgeObsoleteFiles here does not delete files. Instead, it adds the
        // files to be deleted to a job queue, and deletes it in a separate
        // background thread.
        state->db->PurgeObsoleteFiles(job_context, true /* schedule only */);
        state->mu->Lock();
        state->db->SchedulePurge();
        state->mu->Unlock();
      } else {
        state->db->PurgeObsoleteFiles(job_context);
      }
    }
    job_context.Clean();
  }

  delete state;
}
}  // namespace

InternalIterator* DBImpl::NewInternalIterator(
    const ReadOptions& read_options, ColumnFamilyData* cfd,
    SuperVersion* super_version, Arena* arena,
    RangeDelAggregator* range_del_agg) {
  InternalIterator* internal_iter;
  assert(arena != nullptr);
  assert(range_del_agg != nullptr);
  // Need to create internal iterator from the arena.
  MergeIteratorBuilder merge_iter_builder(
      &cfd->internal_comparator(), arena,
      !read_options.total_order_seek &&
          cfd->ioptions()->prefix_extractor != nullptr);
  // Collect iterator for mutable mem
  merge_iter_builder.AddIterator(
      super_version->mem->NewIterator(read_options, arena));
  std::unique_ptr<InternalIterator> range_del_iter;
  Status s;
  if (!read_options.ignore_range_deletions) {
    range_del_iter.reset(
        super_version->mem->NewRangeTombstoneIterator(read_options));
    s = range_del_agg->AddTombstones(std::move(range_del_iter));
  }
  // Collect all needed child iterators for immutable memtables
  if (s.ok()) {
    super_version->imm->AddIterators(read_options, &merge_iter_builder);
    if (!read_options.ignore_range_deletions) {
      s = super_version->imm->AddRangeTombstoneIterators(read_options, arena,
                                                         range_del_agg);
    }
  }
  if (s.ok()) {
    // Collect iterators for files in L0 - Ln
    if (read_options.read_tier != kMemtableTier) {
      super_version->current->AddIterators(read_options, env_options_,
                                           &merge_iter_builder, range_del_agg);
    }
    internal_iter = merge_iter_builder.Finish();
    IterState* cleanup =
        new IterState(this, &mutex_, super_version,
                      read_options.background_purge_on_iterator_cleanup);
    internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, nullptr);

    return internal_iter;
  }
  return NewErrorInternalIterator(s);
}

ColumnFamilyHandle* DBImpl::DefaultColumnFamily() const {
  return default_cf_handle_;
}

Status DBImpl::Get(const ReadOptions& read_options,
                   ColumnFamilyHandle* column_family, const Slice& key,
                   PinnableSlice* value) {
  return GetImpl(read_options, column_family, key, value);
}

Status DBImpl::GetImpl(const ReadOptions& read_options,
                       ColumnFamilyHandle* column_family, const Slice& key,
                       PinnableSlice* pinnable_val, bool* value_found) {
  assert(pinnable_val != nullptr);
  StopWatch sw(env_, stats_, DB_GET);
  PERF_TIMER_GUARD(get_snapshot_time);

  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();

  // Acquire SuperVersion
  SuperVersion* sv = GetAndRefSuperVersion(cfd);

  TEST_SYNC_POINT("DBImpl::GetImpl:1");
  TEST_SYNC_POINT("DBImpl::GetImpl:2");

  SequenceNumber snapshot;
  if (read_options.snapshot != nullptr) {
    snapshot = reinterpret_cast<const SnapshotImpl*>(
        read_options.snapshot)->number_;
  } else {
    // Since we get and reference the super version before getting
    // the snapshot number, without a mutex protection, it is possible
    // that a memtable switch happened in the middle and not all the
    // data for this snapshot is available. But it will contain all
    // the data available in the super version we have, which is also
    // a valid snapshot to read from.
    // We shouldn't get snapshot before finding and referencing the
    // super versipon because a flush happening in between may compact
    // away data for the snapshot, but the snapshot is earlier than the
    // data overwriting it, so users may see wrong results.
    snapshot = versions_->LastSequence();
  }
  TEST_SYNC_POINT("DBImpl::GetImpl:3");
  TEST_SYNC_POINT("DBImpl::GetImpl:4");

  // Prepare to store a list of merge operations if merge occurs.
  MergeContext merge_context;
  RangeDelAggregator range_del_agg(cfd->internal_comparator(), snapshot);

  Status s;
  // First look in the memtable, then in the immutable memtable (if any).
  // s is both in/out. When in, s could either be OK or MergeInProgress.
  // merge_operands will contain the sequence of merges in the latter case.
  LookupKey lkey(key, snapshot);
  PERF_TIMER_STOP(get_snapshot_time);

  bool skip_memtable = (read_options.read_tier == kPersistedTier &&
                        has_unpersisted_data_.load(std::memory_order_relaxed));
  bool done = false;
  if (!skip_memtable) {
    if (sv->mem->Get(lkey, pinnable_val->GetSelf(), &s, &merge_context,
                     &range_del_agg, read_options)) {
      done = true;
      pinnable_val->PinSelf();
      RecordTick(stats_, MEMTABLE_HIT);
    } else if ((s.ok() || s.IsMergeInProgress()) &&
               sv->imm->Get(lkey, pinnable_val->GetSelf(), &s, &merge_context,
                            &range_del_agg, read_options)) {
      done = true;
      pinnable_val->PinSelf();
      RecordTick(stats_, MEMTABLE_HIT);
    }
    if (!done && !s.ok() && !s.IsMergeInProgress()) {
      return s;
    }
  }
  if (!done) {
    PERF_TIMER_GUARD(get_from_output_files_time);
    sv->current->Get(read_options, lkey, pinnable_val, &s, &merge_context,
                     &range_del_agg, value_found);
    RecordTick(stats_, MEMTABLE_MISS);
  }

  {
    PERF_TIMER_GUARD(get_post_process_time);

    ReturnAndCleanupSuperVersion(cfd, sv);

    RecordTick(stats_, NUMBER_KEYS_READ);
    size_t size = pinnable_val->size();
    RecordTick(stats_, BYTES_READ, size);
    MeasureTime(stats_, BYTES_PER_READ, size);
  }
  return s;
}

std::vector<Status> DBImpl::MultiGet(
    const ReadOptions& read_options,
    const std::vector<ColumnFamilyHandle*>& column_family,
    const std::vector<Slice>& keys, std::vector<std::string>* values) {

  StopWatch sw(env_, stats_, DB_MULTIGET);
  PERF_TIMER_GUARD(get_snapshot_time);

  SequenceNumber snapshot;

  struct MultiGetColumnFamilyData {
    ColumnFamilyData* cfd;
    SuperVersion* super_version;
  };
  std::unordered_map<uint32_t, MultiGetColumnFamilyData*> multiget_cf_data;
  // fill up and allocate outside of mutex
  for (auto cf : column_family) {
    auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(cf);
    auto cfd = cfh->cfd();
    if (multiget_cf_data.find(cfd->GetID()) == multiget_cf_data.end()) {
      auto mgcfd = new MultiGetColumnFamilyData();
      mgcfd->cfd = cfd;
      multiget_cf_data.insert({cfd->GetID(), mgcfd});
    }
  }

  mutex_.Lock();
  if (read_options.snapshot != nullptr) {
    snapshot = reinterpret_cast<const SnapshotImpl*>(
        read_options.snapshot)->number_;
  } else {
    snapshot = versions_->LastSequence();
  }
  for (auto mgd_iter : multiget_cf_data) {
    mgd_iter.second->super_version =
        mgd_iter.second->cfd->GetSuperVersion()->Ref();
  }
  mutex_.Unlock();

  // Contain a list of merge operations if merge occurs.
  MergeContext merge_context;

  // Note: this always resizes the values array
  size_t num_keys = keys.size();
  std::vector<Status> stat_list(num_keys);
  values->resize(num_keys);

  // Keep track of bytes that we read for statistics-recording later
  uint64_t bytes_read = 0;
  PERF_TIMER_STOP(get_snapshot_time);

  // For each of the given keys, apply the entire "get" process as follows:
  // First look in the memtable, then in the immutable memtable (if any).
  // s is both in/out. When in, s could either be OK or MergeInProgress.
  // merge_operands will contain the sequence of merges in the latter case.
  for (size_t i = 0; i < num_keys; ++i) {
    merge_context.Clear();
    Status& s = stat_list[i];
    std::string* value = &(*values)[i];

    LookupKey lkey(keys[i], snapshot);
    auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family[i]);
    RangeDelAggregator range_del_agg(cfh->cfd()->internal_comparator(),
                                     snapshot);
    auto mgd_iter = multiget_cf_data.find(cfh->cfd()->GetID());
    assert(mgd_iter != multiget_cf_data.end());
    auto mgd = mgd_iter->second;
    auto super_version = mgd->super_version;
    bool skip_memtable =
        (read_options.read_tier == kPersistedTier &&
         has_unpersisted_data_.load(std::memory_order_relaxed));
    bool done = false;
    if (!skip_memtable) {
      if (super_version->mem->Get(lkey, value, &s, &merge_context,
                                  &range_del_agg, read_options)) {
        done = true;
        // TODO(?): RecordTick(stats_, MEMTABLE_HIT)?
      } else if (super_version->imm->Get(lkey, value, &s, &merge_context,
                                         &range_del_agg, read_options)) {
        done = true;
        // TODO(?): RecordTick(stats_, MEMTABLE_HIT)?
      }
    }
    if (!done) {
      PinnableSlice pinnable_val;
      PERF_TIMER_GUARD(get_from_output_files_time);
      super_version->current->Get(read_options, lkey, &pinnable_val, &s,
                                  &merge_context, &range_del_agg);
      value->assign(pinnable_val.data(), pinnable_val.size());
      // TODO(?): RecordTick(stats_, MEMTABLE_MISS)?
    }

    if (s.ok()) {
      bytes_read += value->size();
    }
  }

  // Post processing (decrement reference counts and record statistics)
  PERF_TIMER_GUARD(get_post_process_time);
  autovector<SuperVersion*> superversions_to_delete;

  // TODO(icanadi) do we need lock here or just around Cleanup()?
  mutex_.Lock();
  for (auto mgd_iter : multiget_cf_data) {
    auto mgd = mgd_iter.second;
    if (mgd->super_version->Unref()) {
      mgd->super_version->Cleanup();
      superversions_to_delete.push_back(mgd->super_version);
    }
  }
  mutex_.Unlock();

  for (auto td : superversions_to_delete) {
    delete td;
  }
  for (auto mgd : multiget_cf_data) {
    delete mgd.second;
  }

  RecordTick(stats_, NUMBER_MULTIGET_CALLS);
  RecordTick(stats_, NUMBER_MULTIGET_KEYS_READ, num_keys);
  RecordTick(stats_, NUMBER_MULTIGET_BYTES_READ, bytes_read);
  MeasureTime(stats_, BYTES_PER_MULTIGET, bytes_read);
  PERF_TIMER_STOP(get_post_process_time);

  return stat_list;
}

Status DBImpl::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
                                  const std::string& column_family_name,
                                  ColumnFamilyHandle** handle) {
  Status s;
  Status persist_options_status;
  *handle = nullptr;

  s = CheckCompressionSupported(cf_options);
  if (s.ok() && immutable_db_options_.allow_concurrent_memtable_write) {
    s = CheckConcurrentWritesSupported(cf_options);
  }
  if (!s.ok()) {
    return s;
  }

  {
    InstrumentedMutexLock l(&mutex_);

    if (versions_->GetColumnFamilySet()->GetColumnFamily(column_family_name) !=
        nullptr) {
      return Status::InvalidArgument("Column family already exists");
    }
    VersionEdit edit;
    edit.AddColumnFamily(column_family_name);
    uint32_t new_id = versions_->GetColumnFamilySet()->GetNextColumnFamilyID();
    edit.SetColumnFamily(new_id);
    edit.SetLogNumber(logfile_number_);
    edit.SetComparatorName(cf_options.comparator->Name());

    // LogAndApply will both write the creation in MANIFEST and create
    // ColumnFamilyData object
    {  // write thread
      WriteThread::Writer w;
      write_thread_.EnterUnbatched(&w, &mutex_);
      // LogAndApply will both write the creation in MANIFEST and create
      // ColumnFamilyData object
      s = versions_->LogAndApply(nullptr, MutableCFOptions(cf_options), &edit,
                                 &mutex_, directories_.GetDbDir(), false,
                                 &cf_options);

      if (s.ok()) {
        // If the column family was created successfully, we then persist
        // the updated RocksDB options under the same single write thread
        persist_options_status = WriteOptionsFile();
      }
      write_thread_.ExitUnbatched(&w);
    }
    if (s.ok()) {
      single_column_family_mode_ = false;
      auto* cfd =
          versions_->GetColumnFamilySet()->GetColumnFamily(column_family_name);
      assert(cfd != nullptr);
      delete InstallSuperVersionAndScheduleWork(
          cfd, nullptr, *cfd->GetLatestMutableCFOptions());

      if (!cfd->mem()->IsSnapshotSupported()) {
        is_snapshot_supported_ = false;
      }

      *handle = new ColumnFamilyHandleImpl(cfd, this, &mutex_);
      ROCKS_LOG_INFO(immutable_db_options_.info_log,
                     "Created column family [%s] (ID %u)",
                     column_family_name.c_str(), (unsigned)cfd->GetID());
    } else {
      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                      "Creating column family [%s] FAILED -- %s",
                      column_family_name.c_str(), s.ToString().c_str());
    }
  }  // InstrumentedMutexLock l(&mutex_)

  // this is outside the mutex
  if (s.ok()) {
    NewThreadStatusCfInfo(
        reinterpret_cast<ColumnFamilyHandleImpl*>(*handle)->cfd());
    if (!persist_options_status.ok()) {
      if (immutable_db_options_.fail_if_options_file_error) {
        s = Status::IOError(
            "ColumnFamily has been created, but unable to persist"
            "options in CreateColumnFamily()",
            persist_options_status.ToString().c_str());
      }
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "Unable to persist options in CreateColumnFamily() -- %s",
                     persist_options_status.ToString().c_str());
    }
  }
  return s;
}

Status DBImpl::DropColumnFamily(ColumnFamilyHandle* column_family) {
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();
  if (cfd->GetID() == 0) {
    return Status::InvalidArgument("Can't drop default column family");
  }

  bool cf_support_snapshot = cfd->mem()->IsSnapshotSupported();

  VersionEdit edit;
  edit.DropColumnFamily();
  edit.SetColumnFamily(cfd->GetID());

  Status s;
  Status options_persist_status;
  {
    InstrumentedMutexLock l(&mutex_);
    if (cfd->IsDropped()) {
      s = Status::InvalidArgument("Column family already dropped!\n");
    }
    if (s.ok()) {
      // we drop column family from a single write thread
      WriteThread::Writer w;
      write_thread_.EnterUnbatched(&w, &mutex_);
      s = versions_->LogAndApply(cfd, *cfd->GetLatestMutableCFOptions(),
                                 &edit, &mutex_);
      if (s.ok()) {
        // If the column family was dropped successfully, we then persist
        // the updated RocksDB options under the same single write thread
        options_persist_status = WriteOptionsFile();
      }
      write_thread_.ExitUnbatched(&w);
    }

    if (!cf_support_snapshot) {
      // Dropped Column Family doesn't support snapshot. Need to recalculate
      // is_snapshot_supported_.
      bool new_is_snapshot_supported = true;
      for (auto c : *versions_->GetColumnFamilySet()) {
        if (!c->IsDropped() && !c->mem()->IsSnapshotSupported()) {
          new_is_snapshot_supported = false;
          break;
        }
      }
      is_snapshot_supported_ = new_is_snapshot_supported;
    }
  }

  if (s.ok()) {
    // Note that here we erase the associated cf_info of the to-be-dropped
    // cfd before its ref-count goes to zero to avoid having to erase cf_info
    // later inside db_mutex.
    EraseThreadStatusCfInfo(cfd);
    assert(cfd->IsDropped());
    auto* mutable_cf_options = cfd->GetLatestMutableCFOptions();
    max_total_in_memory_state_ -= mutable_cf_options->write_buffer_size *
                                  mutable_cf_options->max_write_buffer_number;
    ROCKS_LOG_INFO(immutable_db_options_.info_log,
                   "Dropped column family with id %u\n", cfd->GetID());

    if (!options_persist_status.ok()) {
      if (immutable_db_options_.fail_if_options_file_error) {
        s = Status::IOError(
            "ColumnFamily has been dropped, but unable to persist "
            "options in DropColumnFamily()",
            options_persist_status.ToString().c_str());
      }
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "Unable to persist options in DropColumnFamily() -- %s",
                     options_persist_status.ToString().c_str());
    }
  } else {
    ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                    "Dropping column family with id %u FAILED -- %s\n",
                    cfd->GetID(), s.ToString().c_str());
  }

  return s;
}

bool DBImpl::KeyMayExist(const ReadOptions& read_options,
                         ColumnFamilyHandle* column_family, const Slice& key,
                         std::string* value, bool* value_found) {
  assert(value != nullptr);
  if (value_found != nullptr) {
    // falsify later if key-may-exist but can't fetch value
    *value_found = true;
  }
  ReadOptions roptions = read_options;
  roptions.read_tier = kBlockCacheTier; // read from block cache only
  PinnableSlice pinnable_val;
  auto s = GetImpl(roptions, column_family, key, &pinnable_val, value_found);
  value->assign(pinnable_val.data(), pinnable_val.size());

  // If block_cache is enabled and the index block of the table didn't
  // not present in block_cache, the return value will be Status::Incomplete.
  // In this case, key may still exist in the table.
  return s.ok() || s.IsIncomplete();
}

Iterator* DBImpl::NewIterator(const ReadOptions& read_options,
                              ColumnFamilyHandle* column_family) {
  if (read_options.read_tier == kPersistedTier) {
    return NewErrorIterator(Status::NotSupported(
        "ReadTier::kPersistedData is not yet supported in iterators."));
  }
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();
  if (read_options.managed) {
#ifdef ROCKSDB_LITE
    // not supported in lite version
    return NewErrorIterator(Status::InvalidArgument(
        "Managed Iterators not supported in RocksDBLite."));
#else
    if ((read_options.tailing) || (read_options.snapshot != nullptr) ||
        (is_snapshot_supported_)) {
      return new ManagedIterator(this, read_options, cfd);
    }
    // Managed iter not supported
    return NewErrorIterator(Status::InvalidArgument(
        "Managed Iterators not supported without snapshots."));
#endif
  } else if (read_options.tailing) {
#ifdef ROCKSDB_LITE
    // not supported in lite version
    return nullptr;
#else
    SuperVersion* sv = cfd->GetReferencedSuperVersion(&mutex_);
    auto iter = new ForwardIterator(this, read_options, cfd, sv);
    return NewDBIterator(
        env_, read_options, *cfd->ioptions(), cfd->user_comparator(), iter,
        kMaxSequenceNumber,
        sv->mutable_cf_options.max_sequential_skip_in_iterations,
        sv->version_number);
#endif
  } else {
    SequenceNumber latest_snapshot = versions_->LastSequence();
    SuperVersion* sv = cfd->GetReferencedSuperVersion(&mutex_);

    auto snapshot =
        read_options.snapshot != nullptr
            ? reinterpret_cast<const SnapshotImpl*>(
                read_options.snapshot)->number_
            : latest_snapshot;

    // Try to generate a DB iterator tree in continuous memory area to be
    // cache friendly. Here is an example of result:
    // +-------------------------------+
    // |                               |
    // | ArenaWrappedDBIter            |
    // |  +                            |
    // |  +---> Inner Iterator   ------------+
    // |  |                            |     |
    // |  |    +-- -- -- -- -- -- -- --+     |
    // |  +--- | Arena                 |     |
    // |       |                       |     |
    // |          Allocated Memory:    |     |
    // |       |   +-------------------+     |
    // |       |   | DBIter            | <---+
    // |           |  +                |
    // |       |   |  +-> iter_  ------------+
    // |       |   |                   |     |
    // |       |   +-------------------+     |
    // |       |   | MergingIterator   | <---+
    // |           |  +                |
    // |       |   |  +->child iter1  ------------+
    // |       |   |  |                |          |
    // |           |  +->child iter2  ----------+ |
    // |       |   |  |                |        | |
    // |       |   |  +->child iter3  --------+ | |
    // |           |                   |      | | |
    // |       |   +-------------------+      | | |
    // |       |   | Iterator1         | <--------+
    // |       |   +-------------------+      | |
    // |       |   | Iterator2         | <------+
    // |       |   +-------------------+      |
    // |       |   | Iterator3         | <----+
    // |       |   +-------------------+
    // |       |                       |
    // +-------+-----------------------+
    //
    // ArenaWrappedDBIter inlines an arena area where all the iterators in
    // the iterator tree are allocated in the order of being accessed when
    // querying.
    // Laying out the iterators in the order of being accessed makes it more
    // likely that any iterator pointer is close to the iterator it points to so
    // that they are likely to be in the same cache line and/or page.
    ArenaWrappedDBIter* db_iter = NewArenaWrappedDbIterator(
        env_, read_options, *cfd->ioptions(), cfd->user_comparator(), snapshot,
        sv->mutable_cf_options.max_sequential_skip_in_iterations,
        sv->version_number);

    InternalIterator* internal_iter =
        NewInternalIterator(read_options, cfd, sv, db_iter->GetArena(),
                            db_iter->GetRangeDelAggregator());
    db_iter->SetIterUnderDBIter(internal_iter);

    return db_iter;
  }
  // To stop compiler from complaining
  return nullptr;
}

Status DBImpl::NewIterators(
    const ReadOptions& read_options,
    const std::vector<ColumnFamilyHandle*>& column_families,
    std::vector<Iterator*>* iterators) {
  if (read_options.read_tier == kPersistedTier) {
    return Status::NotSupported(
        "ReadTier::kPersistedData is not yet supported in iterators.");
  }
  iterators->clear();
  iterators->reserve(column_families.size());
  if (read_options.managed) {
#ifdef ROCKSDB_LITE
    return Status::InvalidArgument(
        "Managed interator not supported in RocksDB lite");
#else
    if ((!read_options.tailing) && (read_options.snapshot == nullptr) &&
        (!is_snapshot_supported_)) {
      return Status::InvalidArgument(
          "Managed interator not supported without snapshots");
    }
    for (auto cfh : column_families) {
      auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(cfh)->cfd();
      auto iter = new ManagedIterator(this, read_options, cfd);
      iterators->push_back(iter);
    }
#endif
  } else if (read_options.tailing) {
#ifdef ROCKSDB_LITE
    return Status::InvalidArgument(
        "Tailing interator not supported in RocksDB lite");
#else
    for (auto cfh : column_families) {
      auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(cfh)->cfd();
      SuperVersion* sv = cfd->GetReferencedSuperVersion(&mutex_);
      auto iter = new ForwardIterator(this, read_options, cfd, sv);
      iterators->push_back(NewDBIterator(
          env_, read_options, *cfd->ioptions(), cfd->user_comparator(), iter,
          kMaxSequenceNumber,
          sv->mutable_cf_options.max_sequential_skip_in_iterations,
          sv->version_number));
    }
#endif
  } else {
    SequenceNumber latest_snapshot = versions_->LastSequence();

    for (size_t i = 0; i < column_families.size(); ++i) {
      auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(
          column_families[i])->cfd();
      SuperVersion* sv = cfd->GetReferencedSuperVersion(&mutex_);

      auto snapshot =
          read_options.snapshot != nullptr
              ? reinterpret_cast<const SnapshotImpl*>(
                  read_options.snapshot)->number_
              : latest_snapshot;

      ArenaWrappedDBIter* db_iter = NewArenaWrappedDbIterator(
          env_, read_options, *cfd->ioptions(), cfd->user_comparator(),
          snapshot, sv->mutable_cf_options.max_sequential_skip_in_iterations,
          sv->version_number);
      InternalIterator* internal_iter =
          NewInternalIterator(read_options, cfd, sv, db_iter->GetArena(),
                              db_iter->GetRangeDelAggregator());
      db_iter->SetIterUnderDBIter(internal_iter);
      iterators->push_back(db_iter);
    }
  }

  return Status::OK();
}

const Snapshot* DBImpl::GetSnapshot() { return GetSnapshotImpl(false); }

#ifndef ROCKSDB_LITE
const Snapshot* DBImpl::GetSnapshotForWriteConflictBoundary() {
  return GetSnapshotImpl(true);
}
#endif  // ROCKSDB_LITE

const Snapshot* DBImpl::GetSnapshotImpl(bool is_write_conflict_boundary) {
  int64_t unix_time = 0;
  env_->GetCurrentTime(&unix_time);  // Ignore error
  SnapshotImpl* s = new SnapshotImpl;

  InstrumentedMutexLock l(&mutex_);
  // returns null if the underlying memtable does not support snapshot.
  if (!is_snapshot_supported_) {
    delete s;
    return nullptr;
  }
  return snapshots_.New(s, versions_->LastSequence(), unix_time,
                        is_write_conflict_boundary);
}

void DBImpl::ReleaseSnapshot(const Snapshot* s) {
  const SnapshotImpl* casted_s = reinterpret_cast<const SnapshotImpl*>(s);
  {
    InstrumentedMutexLock l(&mutex_);
    snapshots_.Delete(casted_s);
  }
  delete casted_s;
}

#ifndef ROCKSDB_LITE
Status DBImpl::GetPropertiesOfAllTables(ColumnFamilyHandle* column_family,
                                        TablePropertiesCollection* props) {
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();

  // Increment the ref count
  mutex_.Lock();
  auto version = cfd->current();
  version->Ref();
  mutex_.Unlock();

  auto s = version->GetPropertiesOfAllTables(props);

  // Decrement the ref count
  mutex_.Lock();
  version->Unref();
  mutex_.Unlock();

  return s;
}

Status DBImpl::GetPropertiesOfTablesInRange(ColumnFamilyHandle* column_family,
                                            const Range* range, std::size_t n,
                                            TablePropertiesCollection* props) {
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();

  // Increment the ref count
  mutex_.Lock();
  auto version = cfd->current();
  version->Ref();
  mutex_.Unlock();

  auto s = version->GetPropertiesOfTablesInRange(range, n, props);

  // Decrement the ref count
  mutex_.Lock();
  version->Unref();
  mutex_.Unlock();

  return s;
}

#endif  // ROCKSDB_LITE

const std::string& DBImpl::GetName() const {
  return dbname_;
}

Env* DBImpl::GetEnv() const {
  return env_;
}

Options DBImpl::GetOptions(ColumnFamilyHandle* column_family) const {
  InstrumentedMutexLock l(&mutex_);
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  return Options(BuildDBOptions(immutable_db_options_, mutable_db_options_),
                 cfh->cfd()->GetLatestCFOptions());
}

DBOptions DBImpl::GetDBOptions() const {
  InstrumentedMutexLock l(&mutex_);
  return BuildDBOptions(immutable_db_options_, mutable_db_options_);
}

bool DBImpl::GetProperty(ColumnFamilyHandle* column_family,
                         const Slice& property, std::string* value) {
  const DBPropertyInfo* property_info = GetPropertyInfo(property);
  value->clear();
  auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
  if (property_info == nullptr) {
    return false;
  } else if (property_info->handle_int) {
    uint64_t int_value;
    bool ret_value =
        GetIntPropertyInternal(cfd, *property_info, false, &int_value);
    if (ret_value) {
      *value = ToString(int_value);
    }
    return ret_value;
  } else if (property_info->handle_string) {
    InstrumentedMutexLock l(&mutex_);
    return cfd->internal_stats()->GetStringProperty(*property_info, property,
                                                    value);
  }
  // Shouldn't reach here since exactly one of handle_string and handle_int
  // should be non-nullptr.
  assert(false);
  return false;
}

bool DBImpl::GetMapProperty(ColumnFamilyHandle* column_family,
                            const Slice& property,
                            std::map<std::string, double>* value) {
  const DBPropertyInfo* property_info = GetPropertyInfo(property);
  value->clear();
  auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
  if (property_info == nullptr) {
    return false;
  } else if (property_info->handle_map) {
    InstrumentedMutexLock l(&mutex_);
    return cfd->internal_stats()->GetMapProperty(*property_info, property,
                                                 value);
  }
  // If we reach this point it means that handle_map is not provided for the
  // requested property
  return false;
}

bool DBImpl::GetIntProperty(ColumnFamilyHandle* column_family,
                            const Slice& property, uint64_t* value) {
  const DBPropertyInfo* property_info = GetPropertyInfo(property);
  if (property_info == nullptr || property_info->handle_int == nullptr) {
    return false;
  }
  auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
  return GetIntPropertyInternal(cfd, *property_info, false, value);
}

bool DBImpl::GetIntPropertyInternal(ColumnFamilyData* cfd,
                                    const DBPropertyInfo& property_info,
                                    bool is_locked, uint64_t* value) {
  assert(property_info.handle_int != nullptr);
  if (!property_info.need_out_of_mutex) {
    if (is_locked) {
      mutex_.AssertHeld();
      return cfd->internal_stats()->GetIntProperty(property_info, value, this);
    } else {
      InstrumentedMutexLock l(&mutex_);
      return cfd->internal_stats()->GetIntProperty(property_info, value, this);
    }
  } else {
    SuperVersion* sv = nullptr;
    if (!is_locked) {
      sv = GetAndRefSuperVersion(cfd);
    } else {
      sv = cfd->GetSuperVersion();
    }

    bool ret = cfd->internal_stats()->GetIntPropertyOutOfMutex(
        property_info, sv->current, value);

    if (!is_locked) {
      ReturnAndCleanupSuperVersion(cfd, sv);
    }

    return ret;
  }
}

#ifndef ROCKSDB_LITE
Status DBImpl::ResetStats() {
  InstrumentedMutexLock l(&mutex_);
  for (auto* cfd : *versions_->GetColumnFamilySet()) {
    cfd->internal_stats()->Clear();
  }
  return Status::OK();
}
#endif  // ROCKSDB_LITE

bool DBImpl::GetAggregatedIntProperty(const Slice& property,
                                      uint64_t* aggregated_value) {
  const DBPropertyInfo* property_info = GetPropertyInfo(property);
  if (property_info == nullptr || property_info->handle_int == nullptr) {
    return false;
  }

  uint64_t sum = 0;
  {
    // Needs mutex to protect the list of column families.
    InstrumentedMutexLock l(&mutex_);
    uint64_t value;
    for (auto* cfd : *versions_->GetColumnFamilySet()) {
      if (GetIntPropertyInternal(cfd, *property_info, true, &value)) {
        sum += value;
      } else {
        return false;
      }
    }
  }
  *aggregated_value = sum;
  return true;
}

SuperVersion* DBImpl::GetAndRefSuperVersion(ColumnFamilyData* cfd) {
  // TODO(ljin): consider using GetReferencedSuperVersion() directly
  return cfd->GetThreadLocalSuperVersion(&mutex_);
}

// REQUIRED: this function should only be called on the write thread or if the
// mutex is held.
SuperVersion* DBImpl::GetAndRefSuperVersion(uint32_t column_family_id) {
  auto column_family_set = versions_->GetColumnFamilySet();
  auto cfd = column_family_set->GetColumnFamily(column_family_id);
  if (!cfd) {
    return nullptr;
  }

  return GetAndRefSuperVersion(cfd);
}

void DBImpl::ReturnAndCleanupSuperVersion(ColumnFamilyData* cfd,
                                          SuperVersion* sv) {
  bool unref_sv = !cfd->ReturnThreadLocalSuperVersion(sv);

  if (unref_sv) {
    // Release SuperVersion
    if (sv->Unref()) {
      {
        InstrumentedMutexLock l(&mutex_);
        sv->Cleanup();
      }
      delete sv;
      RecordTick(stats_, NUMBER_SUPERVERSION_CLEANUPS);
    }
    RecordTick(stats_, NUMBER_SUPERVERSION_RELEASES);
  }
}

// REQUIRED: this function should only be called on the write thread.
void DBImpl::ReturnAndCleanupSuperVersion(uint32_t column_family_id,
                                          SuperVersion* sv) {
  auto column_family_set = versions_->GetColumnFamilySet();
  auto cfd = column_family_set->GetColumnFamily(column_family_id);

  // If SuperVersion is held, and we successfully fetched a cfd using
  // GetAndRefSuperVersion(), it must still exist.
  assert(cfd != nullptr);
  ReturnAndCleanupSuperVersion(cfd, sv);
}

// REQUIRED: this function should only be called on the write thread or if the
// mutex is held.
ColumnFamilyHandle* DBImpl::GetColumnFamilyHandle(uint32_t column_family_id) {
  ColumnFamilyMemTables* cf_memtables = column_family_memtables_.get();

  if (!cf_memtables->Seek(column_family_id)) {
    return nullptr;
  }

  return cf_memtables->GetColumnFamilyHandle();
}

void DBImpl::GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
                                         const Range& range,
                                         uint64_t* const count,
                                         uint64_t* const size) {
  ColumnFamilyHandleImpl* cfh =
      reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  ColumnFamilyData* cfd = cfh->cfd();
  SuperVersion* sv = GetAndRefSuperVersion(cfd);

  // Convert user_key into a corresponding internal key.
  InternalKey k1(range.start, kMaxSequenceNumber, kValueTypeForSeek);
  InternalKey k2(range.limit, kMaxSequenceNumber, kValueTypeForSeek);
  MemTable::MemTableStats memStats =
      sv->mem->ApproximateStats(k1.Encode(), k2.Encode());
  MemTable::MemTableStats immStats =
      sv->imm->ApproximateStats(k1.Encode(), k2.Encode());
  *count = memStats.count + immStats.count;
  *size = memStats.size + immStats.size;

  ReturnAndCleanupSuperVersion(cfd, sv);
}

void DBImpl::GetApproximateSizes(ColumnFamilyHandle* column_family,
                                 const Range* range, int n, uint64_t* sizes,
                                 uint8_t include_flags) {
  assert(include_flags & DB::SizeApproximationFlags::INCLUDE_FILES ||
         include_flags & DB::SizeApproximationFlags::INCLUDE_MEMTABLES);
  Version* v;
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();
  SuperVersion* sv = GetAndRefSuperVersion(cfd);
  v = sv->current;

  for (int i = 0; i < n; i++) {
    // Convert user_key into a corresponding internal key.
    InternalKey k1(range[i].start, kMaxSequenceNumber, kValueTypeForSeek);
    InternalKey k2(range[i].limit, kMaxSequenceNumber, kValueTypeForSeek);
    sizes[i] = 0;
    if (include_flags & DB::SizeApproximationFlags::INCLUDE_FILES) {
      sizes[i] += versions_->ApproximateSize(v, k1.Encode(), k2.Encode());
    }
    if (include_flags & DB::SizeApproximationFlags::INCLUDE_MEMTABLES) {
      sizes[i] += sv->mem->ApproximateStats(k1.Encode(), k2.Encode()).size;
      sizes[i] += sv->imm->ApproximateStats(k1.Encode(), k2.Encode()).size;
    }
  }

  ReturnAndCleanupSuperVersion(cfd, sv);
}

std::list<uint64_t>::iterator
DBImpl::CaptureCurrentFileNumberInPendingOutputs() {
  // We need to remember the iterator of our insert, because after the
  // background job is done, we need to remove that element from
  // pending_outputs_.
  pending_outputs_.push_back(versions_->current_next_file_number());
  auto pending_outputs_inserted_elem = pending_outputs_.end();
  --pending_outputs_inserted_elem;
  return pending_outputs_inserted_elem;
}

void DBImpl::ReleaseFileNumberFromPendingOutputs(
    std::list<uint64_t>::iterator v) {
  pending_outputs_.erase(v);
}

#ifndef ROCKSDB_LITE
Status DBImpl::GetUpdatesSince(
    SequenceNumber seq, unique_ptr<TransactionLogIterator>* iter,
    const TransactionLogIterator::ReadOptions& read_options) {

  RecordTick(stats_, GET_UPDATES_SINCE_CALLS);
  if (seq > versions_->LastSequence()) {
    return Status::NotFound("Requested sequence not yet written in the db");
  }
  return wal_manager_.GetUpdatesSince(seq, iter, read_options, versions_.get());
}

Status DBImpl::DeleteFile(std::string name) {
  uint64_t number;
  FileType type;
  WalFileType log_type;
  if (!ParseFileName(name, &number, &type, &log_type) ||
      (type != kTableFile && type != kLogFile)) {
    ROCKS_LOG_ERROR(immutable_db_options_.info_log, "DeleteFile %s failed.\n",
                    name.c_str());
    return Status::InvalidArgument("Invalid file name");
  }

  Status status;
  if (type == kLogFile) {
    // Only allow deleting archived log files
    if (log_type != kArchivedLogFile) {
      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                      "DeleteFile %s failed - not archived log.\n",
                      name.c_str());
      return Status::NotSupported("Delete only supported for archived logs");
    }
    status =
        env_->DeleteFile(immutable_db_options_.wal_dir + "/" + name.c_str());
    if (!status.ok()) {
      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                      "DeleteFile %s failed -- %s.\n", name.c_str(),
                      status.ToString().c_str());
    }
    return status;
  }

  int level;
  FileMetaData* metadata;
  ColumnFamilyData* cfd;
  VersionEdit edit;
  JobContext job_context(next_job_id_.fetch_add(1), true);
  {
    InstrumentedMutexLock l(&mutex_);
    status = versions_->GetMetadataForFile(number, &level, &metadata, &cfd);
    if (!status.ok()) {
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "DeleteFile %s failed. File not found\n", name.c_str());
      job_context.Clean();
      return Status::InvalidArgument("File not found");
    }
    assert(level < cfd->NumberLevels());

    // If the file is being compacted no need to delete.
    if (metadata->being_compacted) {
      ROCKS_LOG_INFO(immutable_db_options_.info_log,
                     "DeleteFile %s Skipped. File about to be compacted\n",
                     name.c_str());
      job_context.Clean();
      return Status::OK();
    }

    // Only the files in the last level can be deleted externally.
    // This is to make sure that any deletion tombstones are not
    // lost. Check that the level passed is the last level.
    auto* vstoreage = cfd->current()->storage_info();
    for (int i = level + 1; i < cfd->NumberLevels(); i++) {
      if (vstoreage->NumLevelFiles(i) != 0) {
        ROCKS_LOG_WARN(immutable_db_options_.info_log,
                       "DeleteFile %s FAILED. File not in last level\n",
                       name.c_str());
        job_context.Clean();
        return Status::InvalidArgument("File not in last level");
      }
    }
    // if level == 0, it has to be the oldest file
    if (level == 0 &&
        vstoreage->LevelFiles(0).back()->fd.GetNumber() != number) {
      ROCKS_LOG_WARN(immutable_db_options_.info_log,
                     "DeleteFile %s failed ---"
                     " target file in level 0 must be the oldest.",
                     name.c_str());
      job_context.Clean();
      return Status::InvalidArgument("File in level 0, but not oldest");
    }
    edit.SetColumnFamily(cfd->GetID());
    edit.DeleteFile(level, number);
    status = versions_->LogAndApply(cfd, *cfd->GetLatestMutableCFOptions(),
                                    &edit, &mutex_, directories_.GetDbDir());
    if (status.ok()) {
      InstallSuperVersionAndScheduleWorkWrapper(
          cfd, &job_context, *cfd->GetLatestMutableCFOptions());
    }
    FindObsoleteFiles(&job_context, false);
  }  // lock released here

  LogFlush(immutable_db_options_.info_log);
  // remove files outside the db-lock
  if (job_context.HaveSomethingToDelete()) {
    // Call PurgeObsoleteFiles() without holding mutex.
    PurgeObsoleteFiles(job_context);
  }
  job_context.Clean();
  return status;
}

Status DBImpl::DeleteFilesInRange(ColumnFamilyHandle* column_family,
                                  const Slice* begin, const Slice* end) {
  Status status;
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  ColumnFamilyData* cfd = cfh->cfd();
  VersionEdit edit;
  std::vector<FileMetaData*> deleted_files;
  JobContext job_context(next_job_id_.fetch_add(1), true);
  {
    InstrumentedMutexLock l(&mutex_);
    Version* input_version = cfd->current();

    auto* vstorage = input_version->storage_info();
    for (int i = 1; i < cfd->NumberLevels(); i++) {
      if (vstorage->LevelFiles(i).empty() ||
          !vstorage->OverlapInLevel(i, begin, end)) {
        continue;
      }
      std::vector<FileMetaData*> level_files;
      InternalKey begin_storage, end_storage, *begin_key, *end_key;
      if (begin == nullptr) {
        begin_key = nullptr;
      } else {
        begin_storage.SetMaxPossibleForUserKey(*begin);
        begin_key = &begin_storage;
      }
      if (end == nullptr) {
        end_key = nullptr;
      } else {
        end_storage.SetMinPossibleForUserKey(*end);
        end_key = &end_storage;
      }

      vstorage->GetOverlappingInputs(i, begin_key, end_key, &level_files, -1,
                                     nullptr, false);
      FileMetaData* level_file;
      for (uint32_t j = 0; j < level_files.size(); j++) {
        level_file = level_files[j];
        if (((begin == nullptr) ||
             (cfd->internal_comparator().user_comparator()->Compare(
                  level_file->smallest.user_key(), *begin) >= 0)) &&
            ((end == nullptr) ||
             (cfd->internal_comparator().user_comparator()->Compare(
                  level_file->largest.user_key(), *end) <= 0))) {
          if (level_file->being_compacted) {
            continue;
          }
          edit.SetColumnFamily(cfd->GetID());
          edit.DeleteFile(i, level_file->fd.GetNumber());
          deleted_files.push_back(level_file);
          level_file->being_compacted = true;
        }
      }
    }
    if (edit.GetDeletedFiles().empty()) {
      job_context.Clean();
      return Status::OK();
    }
    input_version->Ref();
    status = versions_->LogAndApply(cfd, *cfd->GetLatestMutableCFOptions(),
                                    &edit, &mutex_, directories_.GetDbDir());
    if (status.ok()) {
      InstallSuperVersionAndScheduleWorkWrapper(
          cfd, &job_context, *cfd->GetLatestMutableCFOptions());
    }
    for (auto* deleted_file : deleted_files) {
      deleted_file->being_compacted = false;
    }
    input_version->Unref();
    FindObsoleteFiles(&job_context, false);
  }  // lock released here

  LogFlush(immutable_db_options_.info_log);
  // remove files outside the db-lock
  if (job_context.HaveSomethingToDelete()) {
    // Call PurgeObsoleteFiles() without holding mutex.
    PurgeObsoleteFiles(job_context);
  }
  job_context.Clean();
  return status;
}

void DBImpl::GetLiveFilesMetaData(std::vector<LiveFileMetaData>* metadata) {
  InstrumentedMutexLock l(&mutex_);
  versions_->GetLiveFilesMetaData(metadata);
}

void DBImpl::GetColumnFamilyMetaData(
    ColumnFamilyHandle* column_family,
    ColumnFamilyMetaData* cf_meta) {
  assert(column_family);
  auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
  auto* sv = GetAndRefSuperVersion(cfd);
  sv->current->GetColumnFamilyMetaData(cf_meta);
  ReturnAndCleanupSuperVersion(cfd, sv);
}

#endif  // ROCKSDB_LITE

Status DBImpl::CheckConsistency() {
  mutex_.AssertHeld();
  std::vector<LiveFileMetaData> metadata;
  versions_->GetLiveFilesMetaData(&metadata);

  std::string corruption_messages;
  for (const auto& md : metadata) {
    // md.name has a leading "/".
    std::string file_path = md.db_path + md.name;

    uint64_t fsize = 0;
    Status s = env_->GetFileSize(file_path, &fsize);
    if (!s.ok() &&
        env_->GetFileSize(Rocks2LevelTableFileName(file_path), &fsize).ok()) {
      s = Status::OK();
    }
    if (!s.ok()) {
      corruption_messages +=
          "Can't access " + md.name + ": " + s.ToString() + "\n";
    } else if (fsize != md.size) {
      corruption_messages += "Sst file size mismatch: " + file_path +
                             ". Size recorded in manifest " +
                             ToString(md.size) + ", actual size " +
                             ToString(fsize) + "\n";
    }
  }
  if (corruption_messages.size() == 0) {
    return Status::OK();
  } else {
    return Status::Corruption(corruption_messages);
  }
}

Status DBImpl::GetDbIdentity(std::string& identity) const {
  std::string idfilename = IdentityFileName(dbname_);
  const EnvOptions soptions;
  unique_ptr<SequentialFileReader> id_file_reader;
  Status s;
  {
    unique_ptr<SequentialFile> idfile;
    s = env_->NewSequentialFile(idfilename, &idfile, soptions);
    if (!s.ok()) {
      return s;
    }
    id_file_reader.reset(new SequentialFileReader(std::move(idfile)));
  }

  uint64_t file_size;
  s = env_->GetFileSize(idfilename, &file_size);
  if (!s.ok()) {
    return s;
  }
  char* buffer = reinterpret_cast<char*>(alloca(file_size));
  Slice id;
  s = id_file_reader->Read(static_cast<size_t>(file_size), &id, buffer);
  if (!s.ok()) {
    return s;
  }
  identity.assign(id.ToString());
  // If last character is '\n' remove it from identity
  if (identity.size() > 0 && identity.back() == '\n') {
    identity.pop_back();
  }
  return s;
}

// Default implementation -- returns not supported status
Status DB::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
                              const std::string& column_family_name,
                              ColumnFamilyHandle** handle) {
  return Status::NotSupported("");
}
Status DB::DropColumnFamily(ColumnFamilyHandle* column_family) {
  return Status::NotSupported("");
}
Status DB::DestroyColumnFamilyHandle(ColumnFamilyHandle* column_family) {
  delete column_family;
  return Status::OK();
}

DB::~DB() { }

Status DB::ListColumnFamilies(const DBOptions& db_options,
                              const std::string& name,
                              std::vector<std::string>* column_families) {
  return VersionSet::ListColumnFamilies(column_families, name, db_options.env);
}

Snapshot::~Snapshot() {
}

Status DestroyDB(const std::string& dbname, const Options& options) {
  const ImmutableDBOptions soptions(SanitizeOptions(dbname, options));
  Env* env = soptions.env;
  std::vector<std::string> filenames;

  // Ignore error in case directory does not exist
  env->GetChildren(dbname, &filenames);

  FileLock* lock;
  const std::string lockname = LockFileName(dbname);
  Status result = env->LockFile(lockname, &lock);
  if (result.ok()) {
    uint64_t number;
    FileType type;
    InfoLogPrefix info_log_prefix(!soptions.db_log_dir.empty(), dbname);
    for (size_t i = 0; i < filenames.size(); i++) {
      if (ParseFileName(filenames[i], &number, info_log_prefix.prefix, &type) &&
          type != kDBLockFile) {  // Lock file will be deleted at end
        Status del;
        std::string path_to_delete = dbname + "/" + filenames[i];
        if (type == kMetaDatabase) {
          del = DestroyDB(path_to_delete, options);
        } else if (type == kTableFile) {
          del = DeleteSSTFile(&soptions, path_to_delete, 0);
        } else {
          del = env->DeleteFile(path_to_delete);
        }
        if (result.ok() && !del.ok()) {
          result = del;
        }
      }
    }

    for (size_t path_id = 0; path_id < options.db_paths.size(); path_id++) {
      const auto& db_path = options.db_paths[path_id];
      env->GetChildren(db_path.path, &filenames);
      for (size_t i = 0; i < filenames.size(); i++) {
        if (ParseFileName(filenames[i], &number, &type) &&
            type == kTableFile) {  // Lock file will be deleted at end
          std::string table_path = db_path.path + "/" + filenames[i];
          Status del = DeleteSSTFile(&soptions, table_path,
                                     static_cast<uint32_t>(path_id));
          if (result.ok() && !del.ok()) {
            result = del;
          }
        }
      }
    }

    std::vector<std::string> walDirFiles;
    std::string archivedir = ArchivalDirectory(dbname);
    if (dbname != soptions.wal_dir) {
      env->GetChildren(soptions.wal_dir, &walDirFiles);
      archivedir = ArchivalDirectory(soptions.wal_dir);
    }

    // Delete log files in the WAL dir
    for (const auto& file : walDirFiles) {
      if (ParseFileName(file, &number, &type) && type == kLogFile) {
        Status del = env->DeleteFile(soptions.wal_dir + "/" + file);
        if (result.ok() && !del.ok()) {
          result = del;
        }
      }
    }

    std::vector<std::string> archiveFiles;
    env->GetChildren(archivedir, &archiveFiles);
    // Delete archival files.
    for (size_t i = 0; i < archiveFiles.size(); ++i) {
      if (ParseFileName(archiveFiles[i], &number, &type) &&
          type == kLogFile) {
        Status del = env->DeleteFile(archivedir + "/" + archiveFiles[i]);
        if (result.ok() && !del.ok()) {
          result = del;
        }
      }
    }

    // ignore case where no archival directory is present
    env->DeleteDir(archivedir);

    env->UnlockFile(lock);  // Ignore error since state is already gone
    env->DeleteFile(lockname);
    env->DeleteDir(dbname);  // Ignore error in case dir contains other files
    env->DeleteDir(soptions.wal_dir);
  }
  return result;
}

Status DBImpl::WriteOptionsFile() {
#ifndef ROCKSDB_LITE
  mutex_.AssertHeld();

  std::vector<std::string> cf_names;
  std::vector<ColumnFamilyOptions> cf_opts;

  // This part requires mutex to protect the column family options
  for (auto cfd : *versions_->GetColumnFamilySet()) {
    if (cfd->IsDropped()) {
      continue;
    }
    cf_names.push_back(cfd->GetName());
    cf_opts.push_back(cfd->GetLatestCFOptions());
  }

  // Unlock during expensive operations.  New writes cannot get here
  // because the single write thread ensures all new writes get queued.
  DBOptions db_options =
      BuildDBOptions(immutable_db_options_, mutable_db_options_);
  mutex_.Unlock();

  std::string file_name =
      TempOptionsFileName(GetName(), versions_->NewFileNumber());
  Status s =
      PersistRocksDBOptions(db_options, cf_names, cf_opts, file_name, GetEnv());

  if (s.ok()) {
    s = RenameTempFileToOptionsFile(file_name);
  }
  mutex_.Lock();
  return s;
#else
  return Status::OK();
#endif  // !ROCKSDB_LITE
}

#ifndef ROCKSDB_LITE
namespace {
void DeleteOptionsFilesHelper(const std::map<uint64_t, std::string>& filenames,
                              const size_t num_files_to_keep,
                              const std::shared_ptr<Logger>& info_log,
                              Env* env) {
  if (filenames.size() <= num_files_to_keep) {
    return;
  }
  for (auto iter = std::next(filenames.begin(), num_files_to_keep);
       iter != filenames.end(); ++iter) {
    if (!env->DeleteFile(iter->second).ok()) {
      ROCKS_LOG_WARN(info_log, "Unable to delete options file %s",
                     iter->second.c_str());
    }
  }
}
}  // namespace
#endif  // !ROCKSDB_LITE

Status DBImpl::DeleteObsoleteOptionsFiles() {
#ifndef ROCKSDB_LITE
  std::vector<std::string> filenames;
  // use ordered map to store keep the filenames sorted from the newest
  // to the oldest.
  std::map<uint64_t, std::string> options_filenames;
  Status s;
  s = GetEnv()->GetChildren(GetName(), &filenames);
  if (!s.ok()) {
    return s;
  }
  for (auto& filename : filenames) {
    uint64_t file_number;
    FileType type;
    if (ParseFileName(filename, &file_number, &type) && type == kOptionsFile) {
      options_filenames.insert(
          {std::numeric_limits<uint64_t>::max() - file_number,
           GetName() + "/" + filename});
    }
  }

  // Keeps the latest 2 Options file
  const size_t kNumOptionsFilesKept = 2;
  DeleteOptionsFilesHelper(options_filenames, kNumOptionsFilesKept,
                           immutable_db_options_.info_log, GetEnv());
  return Status::OK();
#else
  return Status::OK();
#endif  // !ROCKSDB_LITE
}

Status DBImpl::RenameTempFileToOptionsFile(const std::string& file_name) {
#ifndef ROCKSDB_LITE
  Status s;

  versions_->options_file_number_ = versions_->NewFileNumber();
  std::string options_file_name =
      OptionsFileName(GetName(), versions_->options_file_number_);
  // Retry if the file name happen to conflict with an existing one.
  s = GetEnv()->RenameFile(file_name, options_file_name);

  DeleteObsoleteOptionsFiles();
  return s;
#else
  return Status::OK();
#endif  // !ROCKSDB_LITE
}

#ifdef ROCKSDB_USING_THREAD_STATUS

void DBImpl::NewThreadStatusCfInfo(
    ColumnFamilyData* cfd) const {
  if (immutable_db_options_.enable_thread_tracking) {
    ThreadStatusUtil::NewColumnFamilyInfo(this, cfd, cfd->GetName(),
                                          cfd->ioptions()->env);
  }
}

void DBImpl::EraseThreadStatusCfInfo(
    ColumnFamilyData* cfd) const {
  if (immutable_db_options_.enable_thread_tracking) {
    ThreadStatusUtil::EraseColumnFamilyInfo(cfd);
  }
}

void DBImpl::EraseThreadStatusDbInfo() const {
  if (immutable_db_options_.enable_thread_tracking) {
    ThreadStatusUtil::EraseDatabaseInfo(this);
  }
}

#else
void DBImpl::NewThreadStatusCfInfo(
    ColumnFamilyData* cfd) const {
}

void DBImpl::EraseThreadStatusCfInfo(
    ColumnFamilyData* cfd) const {
}

void DBImpl::EraseThreadStatusDbInfo() const {
}
#endif  // ROCKSDB_USING_THREAD_STATUS

//
// A global method that can dump out the build version
void DumpRocksDBBuildVersion(Logger * log) {
#if !defined(IOS_CROSS_COMPILE)
  // if we compile with Xcode, we don't run build_detect_vesion, so we don't
  // generate util/build_version.cc
  ROCKS_LOG_HEADER(log, "RocksDB version: %d.%d.%d\n", ROCKSDB_MAJOR,
                   ROCKSDB_MINOR, ROCKSDB_PATCH);
  ROCKS_LOG_HEADER(log, "Git sha %s", rocksdb_build_git_sha);
  ROCKS_LOG_HEADER(log, "Compile date %s", rocksdb_build_compile_date);
#endif
}

#ifndef ROCKSDB_LITE
SequenceNumber DBImpl::GetEarliestMemTableSequenceNumber(SuperVersion* sv,
                                                         bool include_history) {
  // Find the earliest sequence number that we know we can rely on reading
  // from the memtable without needing to check sst files.
  SequenceNumber earliest_seq =
      sv->imm->GetEarliestSequenceNumber(include_history);
  if (earliest_seq == kMaxSequenceNumber) {
    earliest_seq = sv->mem->GetEarliestSequenceNumber();
  }
  assert(sv->mem->GetEarliestSequenceNumber() >= earliest_seq);

  return earliest_seq;
}
#endif  // ROCKSDB_LITE

#ifndef ROCKSDB_LITE
Status DBImpl::GetLatestSequenceForKey(SuperVersion* sv, const Slice& key,
                                       bool cache_only, SequenceNumber* seq,
                                       bool* found_record_for_key) {
  Status s;
  MergeContext merge_context;
  RangeDelAggregator range_del_agg(sv->mem->GetInternalKeyComparator(),
                                   kMaxSequenceNumber);

  ReadOptions read_options;
  SequenceNumber current_seq = versions_->LastSequence();
  LookupKey lkey(key, current_seq);

  *seq = kMaxSequenceNumber;
  *found_record_for_key = false;

  // Check if there is a record for this key in the latest memtable
  sv->mem->Get(lkey, nullptr, &s, &merge_context, &range_del_agg, seq,
               read_options);

  if (!(s.ok() || s.IsNotFound() || s.IsMergeInProgress())) {
    // unexpected error reading memtable.
    ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                    "Unexpected status returned from MemTable::Get: %s\n",
                    s.ToString().c_str());

    return s;
  }

  if (*seq != kMaxSequenceNumber) {
    // Found a sequence number, no need to check immutable memtables
    *found_record_for_key = true;
    return Status::OK();
  }

  // Check if there is a record for this key in the immutable memtables
  sv->imm->Get(lkey, nullptr, &s, &merge_context, &range_del_agg, seq,
               read_options);

  if (!(s.ok() || s.IsNotFound() || s.IsMergeInProgress())) {
    // unexpected error reading memtable.
    ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                    "Unexpected status returned from MemTableList::Get: %s\n",
                    s.ToString().c_str());

    return s;
  }

  if (*seq != kMaxSequenceNumber) {
    // Found a sequence number, no need to check memtable history
    *found_record_for_key = true;
    return Status::OK();
  }

  // Check if there is a record for this key in the immutable memtables
  sv->imm->GetFromHistory(lkey, nullptr, &s, &merge_context, &range_del_agg,
                          seq, read_options);

  if (!(s.ok() || s.IsNotFound() || s.IsMergeInProgress())) {
    // unexpected error reading memtable.
    ROCKS_LOG_ERROR(
        immutable_db_options_.info_log,
        "Unexpected status returned from MemTableList::GetFromHistory: %s\n",
        s.ToString().c_str());

    return s;
  }

  if (*seq != kMaxSequenceNumber) {
    // Found a sequence number, no need to check SST files
    *found_record_for_key = true;
    return Status::OK();
  }

  // TODO(agiardullo): possible optimization: consider checking cached
  // SST files if cache_only=true?
  if (!cache_only) {
    // Check tables
    sv->current->Get(read_options, lkey, nullptr, &s, &merge_context,
                     &range_del_agg, nullptr /* value_found */,
                     found_record_for_key, seq);

    if (!(s.ok() || s.IsNotFound() || s.IsMergeInProgress())) {
      // unexpected error reading SST files
      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                      "Unexpected status returned from Version::Get: %s\n",
                      s.ToString().c_str());

      return s;
    }
  }

  return Status::OK();
}

Status DBImpl::IngestExternalFile(
    ColumnFamilyHandle* column_family,
    const std::vector<std::string>& external_files,
    const IngestExternalFileOptions& ingestion_options) {
  Status status;
  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
  auto cfd = cfh->cfd();

  ExternalSstFileIngestionJob ingestion_job(env_, versions_.get(), cfd,
                                            immutable_db_options_, env_options_,
                                            &snapshots_, ingestion_options);

  std::list<uint64_t>::iterator pending_output_elem;
  {
    InstrumentedMutexLock l(&mutex_);
    if (!bg_error_.ok()) {
      // Don't ingest files when there is a bg_error
      return bg_error_;
    }

    // Make sure that bg cleanup wont delete the files that we are ingesting
    pending_output_elem = CaptureCurrentFileNumberInPendingOutputs();
  }

  status = ingestion_job.Prepare(external_files);
  if (!status.ok()) {
    return status;
  }

  TEST_SYNC_POINT("DBImpl::AddFile:Start");
  {
    // Lock db mutex
    InstrumentedMutexLock l(&mutex_);
    TEST_SYNC_POINT("DBImpl::AddFile:MutexLock");

    // Stop writes to the DB
    WriteThread::Writer w;
    write_thread_.EnterUnbatched(&w, &mutex_);

    num_running_ingest_file_++;

    // We cannot ingest a file into a dropped CF
    if (cfd->IsDropped()) {
      status = Status::InvalidArgument(
          "Cannot ingest an external file into a dropped CF");
    }

    // Figure out if we need to flush the memtable first
    if (status.ok()) {
      bool need_flush = false;
      status = ingestion_job.NeedsFlush(&need_flush);
      TEST_SYNC_POINT_CALLBACK("DBImpl::IngestExternalFile:NeedFlush",
                               &need_flush);
      if (status.ok() && need_flush) {
        mutex_.Unlock();
        status = FlushMemTable(cfd, FlushOptions(), true /* writes_stopped */);
        mutex_.Lock();
      }
    }

    // Run the ingestion job
    if (status.ok()) {
      status = ingestion_job.Run();
    }

    // Install job edit [Mutex will be unlocked here]
    auto mutable_cf_options = cfd->GetLatestMutableCFOptions();
    if (status.ok()) {
      status =
          versions_->LogAndApply(cfd, *mutable_cf_options, ingestion_job.edit(),
                                 &mutex_, directories_.GetDbDir());
    }
    if (status.ok()) {
      delete InstallSuperVersionAndScheduleWork(cfd, nullptr,
                                                *mutable_cf_options);
    }

    // Resume writes to the DB
    write_thread_.ExitUnbatched(&w);

    // Update stats
    if (status.ok()) {
      ingestion_job.UpdateStats();
    }

    ReleaseFileNumberFromPendingOutputs(pending_output_elem);

    num_running_ingest_file_--;
    if (num_running_ingest_file_ == 0) {
      bg_cv_.SignalAll();
    }

    TEST_SYNC_POINT("DBImpl::AddFile:MutexUnlock");
  }
  // mutex_ is unlocked here

  // Cleanup
  ingestion_job.Cleanup(status);

  if (status.ok()) {
    NotifyOnExternalFileIngested(cfd, ingestion_job);
  }

  return status;
}

void DBImpl::NotifyOnExternalFileIngested(
    ColumnFamilyData* cfd, const ExternalSstFileIngestionJob& ingestion_job) {
#ifndef ROCKSDB_LITE
  if (immutable_db_options_.listeners.empty()) {
    return;
  }

  for (const IngestedFileInfo& f : ingestion_job.files_to_ingest()) {
    ExternalFileIngestionInfo info;
    info.cf_name = cfd->GetName();
    info.external_file_path = f.external_file_path;
    info.internal_file_path = f.internal_file_path;
    info.global_seqno = f.assigned_seqno;
    info.table_properties = f.table_properties;
    for (auto listener : immutable_db_options_.listeners) {
      listener->OnExternalFileIngested(this, info);
    }
  }

#endif
}

void DBImpl::WaitForIngestFile() {
  mutex_.AssertHeld();
  while (num_running_ingest_file_ > 0) {
    bg_cv_.Wait();
  }
}

#endif  // ROCKSDB_LITE

}  // namespace rocksdb