auto chartLinksCache =
      std::unordered_map<std::pair<time_t, time_t>, ChartLinks> {};
  auto chartLinkGenerator = [startTs, endTs, this, &chartLinksCache]() mutable {
    if (auto chartLinks = folly::get_optional(
            chartLinksCache, std::make_pair(startTs, endTs))) {
      LOG(INFO) << "got from cache" << " " << startTs << " " << endTs;
      return *chartLinks;
    }
    auto chartLinks = genChartLinks(startTs, endTs);
    LOG(INFO) << "not from cache " << " " << startTs << " " << endTs << "size"
              << chartLinksCache.size();
    chartLinksCache.emplace(std::make_pair(startTs, endTs), chartLinks);
    return chartLinks;
  };