Status DBImpl::Recover()

in db/db_impl.cc [292:383]
70 lines of code
17 McCabe index (conditional complexity)

Status DBImpl::Recover(VersionEdit* edit, bool* save_manifest) {
  mutex_.AssertHeld();

  // Ignore error from CreateDir since the creation of the DB is
  // committed only when the descriptor is created, and this directory
  // may already exist from a previous failed creation attempt.
  env_->CreateDir(dbname_);
  assert(db_lock_ == nullptr);
  Status s = env_->LockFile(LockFileName(dbname_), &db_lock_);
  if (!s.ok()) {
    return s;
  }

  if (!env_->FileExists(CurrentFileName(dbname_))) {
    if (options_.create_if_missing) {
      Log(options_.info_log, "Creating DB %s since it was missing.",
          dbname_.c_str());
      s = NewDB();
      if (!s.ok()) {
        return s;
      }
    } else {
      return Status::InvalidArgument(
          dbname_, "does not exist (create_if_missing is false)");
    }
  } else {
    if (options_.error_if_exists) {
      return Status::InvalidArgument(dbname_,
                                     "exists (error_if_exists is true)");
    }
  }

  s = versions_->Recover(save_manifest);
  if (!s.ok()) {
    return s;
  }
  SequenceNumber max_sequence(0);

  // Recover from all newer log files than the ones named in the
  // descriptor (new log files may have been added by the previous
  // incarnation without registering them in the descriptor).
  //
  // Note that PrevLogNumber() is no longer used, but we pay
  // attention to it in case we are recovering a database
  // produced by an older version of leveldb.
  const uint64_t min_log = versions_->LogNumber();
  const uint64_t prev_log = versions_->PrevLogNumber();
  std::vector<std::string> filenames;
  s = env_->GetChildren(dbname_, &filenames);
  if (!s.ok()) {
    return s;
  }
  std::set<uint64_t> expected;
  versions_->AddLiveFiles(&expected);
  uint64_t number;
  FileType type;
  std::vector<uint64_t> logs;
  for (size_t i = 0; i < filenames.size(); i++) {
    if (ParseFileName(filenames[i], &number, &type)) {
      expected.erase(number);
      if (type == kLogFile && ((number >= min_log) || (number == prev_log)))
        logs.push_back(number);
    }
  }
  if (!expected.empty()) {
    char buf[50];
    std::snprintf(buf, sizeof(buf), "%d missing files; e.g.",
                  static_cast<int>(expected.size()));
    return Status::Corruption(buf, TableFileName(dbname_, *(expected.begin())));
  }

  // Recover in the order in which the logs were generated
  std::sort(logs.begin(), logs.end());
  for (size_t i = 0; i < logs.size(); i++) {
    s = RecoverLogFile(logs[i], (i == logs.size() - 1), save_manifest, edit,
                       &max_sequence);
    if (!s.ok()) {
      return s;
    }

    // The previous incarnation may not have written any MANIFEST
    // records after allocating this log number.  So we manually
    // update the file number allocation counter in VersionSet.
    versions_->MarkFileNumberUsed(logs[i]);
  }

  if (versions_->LastSequence() < max_sequence) {
    versions_->SetLastSequence(max_sequence);
  }

  return Status::OK();
}