void DBImpl::RemoveObsoleteFiles()

in db/db_impl.cc [225:290]
51 lines of code
15 McCabe index (conditional complexity)

void DBImpl::RemoveObsoleteFiles() {
  mutex_.AssertHeld();

  if (!bg_error_.ok()) {
    // After a background error, we don't know whether a new version may
    // or may not have been committed, so we cannot safely garbage collect.
    return;
  }

  // Make a set of all of the live files
  std::set<uint64_t> live = pending_outputs_;
  versions_->AddLiveFiles(&live);

  std::vector<std::string> filenames;
  env_->GetChildren(dbname_, &filenames);  // Ignoring errors on purpose
  uint64_t number;
  FileType type;
  std::vector<std::string> files_to_delete;
  for (std::string& filename : filenames) {
    if (ParseFileName(filename, &number, &type)) {
      bool keep = true;
      switch (type) {
        case kLogFile:
          keep = ((number >= versions_->LogNumber()) ||
                  (number == versions_->PrevLogNumber()));
          break;
        case kDescriptorFile:
          // Keep my manifest file, and any newer incarnations'
          // (in case there is a race that allows other incarnations)
          keep = (number >= versions_->ManifestFileNumber());
          break;
        case kTableFile:
          keep = (live.find(number) != live.end());
          break;
        case kTempFile:
          // Any temp files that are currently being written to must
          // be recorded in pending_outputs_, which is inserted into "live"
          keep = (live.find(number) != live.end());
          break;
        case kCurrentFile:
        case kDBLockFile:
        case kInfoLogFile:
          keep = true;
          break;
      }

      if (!keep) {
        files_to_delete.push_back(std::move(filename));
        if (type == kTableFile) {
          table_cache_->Evict(number);
        }
        Log(options_.info_log, "Delete type=%d #%lld\n", static_cast<int>(type),
            static_cast<unsigned long long>(number));
      }
    }
  }

  // While deleting all files unblock other threads. All files being deleted
  // have unique names which will not collide with newly created files and
  // are therefore safe to delete while allowing other threads to proceed.
  mutex_.Unlock();
  for (const std::string& filename : files_to_delete) {
    env_->RemoveFile(dbname_ + "/" + filename);
  }
  mutex_.Lock();
}