And waits for them. That's pointless.
{
    return ((settings.min_rows_to_fsync_after_merge && input_rows >= settings.min_rows_to_fsync_after_merge)
        || (settings.min_compressed_bytes_to_fsync_after_merge && input_bytes >= settings.min_compressed_bytes_to_fsync_after_merge));
}
MergeTreeData::MutableDataPartPtr MergeTreeDataMergerMutator::mergePartsToTemporaryPart(
    const FutureMergedMutatedPart & future_part,
    const StorageMetadataPtr & metadata_snapshot,
    MergeList::Entry & merge_entry,
    TableLockHolder & holder,
    time_t time_of_merge,
    ContextPtr context,
    const ReservationPtr & space_reservation,
    bool deduplicate,
    const Names & deduplicate_by_columns,
    const MergeTreeData::MergingParams & merging_params,
    const IMergeTreeDataPart * parent_part,
    const String & prefix)
{
    const String tmp_prefix = parent_part ? prefix : "tmp_merge_";
    if (merges_blocker.isCancelled())
        throw Exception("Cancelled merging parts", ErrorCodes::ABORTED);
    
    
    if (isTTLMergeType(future_part.merge_type) && ttl_merges_blocker.isCancelled())
        throw Exception("Cancelled merging parts with TTL", ErrorCodes::ABORTED);
    const MergeTreeData::DataPartsVector & parts = future_part.parts;