And waits for them. That's pointless.
if (final && optimize_skip_merged_partitions && parts.size() == 1 && parts[0]->info.level > 0 &&
        (!metadata_snapshot->hasAnyTTL() || parts[0]->checkAllTTLCalculated(metadata_snapshot)))
    {
        return SelectPartsDecision::NOTHING_TO_MERGE;
    }
    auto it = parts.begin();
    auto prev_it = it;
    UInt64 sum_bytes = 0;
    while (it != parts.end())
    {
        
        if ((it != parts.begin() || parts.size() == 1) && !can_merge(*prev_it, *it, out_disable_reason))
        {
            return SelectPartsDecision::CANNOT_SELECT;
        }
        sum_bytes += (*it)->getBytesOnDisk();
        prev_it = it;
        ++it;
    }
    
    auto required_disk_space = sum_bytes * DISK_USAGE_COEFFICIENT_TO_SELECT;
    if (available_disk_space <= required_disk_space)
    {
        time_t now = time(nullptr);
        if (now - disk_space_warning_time > 3600)
        {
            disk_space_warning_time = now;
            LOG_WARNING(log,