diff --git a/src/silo/prepare_dataset.cpp b/src/silo/prepare_dataset.cpp
index df27cc00b..8ed80c31e 100644
--- a/src/silo/prepare_dataset.cpp
+++ b/src/silo/prepare_dataset.cpp
@@ -240,15 +240,15 @@ std::unordered_map<std::string, silo::common::Date> sortMetadataFile(
       silo::common::Date date;
    };
    std::vector<RowWithDate> rows;
-   rows.reserve(chunk.size);
 
    for (auto& row : metadata_reader.reader) {
+      std::this_thread::sleep_for(std::chrono::nanoseconds(1));
       const auto primary_key = row[sort_chunk_config.primary_key_name].get();
       const auto date_str = row[sort_chunk_config.date_column_to_sort_by].get();
 
       const silo::common::Date date = silo::common::stringToDate(date_str);
 
-      rows.push_back({row, date});
+      rows.emplace_back(row, date);
 
       primary_key_to_date[primary_key] = date;
    }
diff --git a/src/silo/preprocessing/partition.cpp b/src/silo/preprocessing/partition.cpp
index 6250392a3..4013cce49 100644
--- a/src/silo/preprocessing/partition.cpp
+++ b/src/silo/preprocessing/partition.cpp
@@ -231,13 +231,12 @@ void Chunk::addChunk(Chunk&& other) {
    count_of_sequences += other.count_of_sequences;
 
    auto copy_of_my_lineages = std::move(pango_lineages);
-   pango_lineages.clear();
    std::merge(
       copy_of_my_lineages.begin(),
       copy_of_my_lineages.end(),
       other.pango_lineages.begin(),
       other.pango_lineages.end(),
-      pango_lineages.begin()
+      std::back_inserter(pango_lineages)
    );
 }