std::unordered_map<std::pair<time_t, time_t>, ChartLinks> chartLinksCache;
  auto chartLinkGenerator = [startTs, endTs, this, &chartLinksCache]() {
    if (auto chartLinks = folly::get_optional(
            chartLinksCache, std::make_pair(startTs, endTs))) {
      return *chartLinks;
    }
    auto chartLinks = genChartLinks(startTs, endTs);
    chartLinksCache.emplace(std::make_pair(startTs, endTs), chartLinks);
    return chartLinks;
  };