And waits for them. That's pointless.
{
        replica_to_execute_merge = merge_strategy_picker.pickReplicaToExecuteMerge(entry);
        replica_to_execute_merge_picked = true;
        if (replica_to_execute_merge)
        {
            LOG_DEBUG(log,
                "Prefer fetching part {} from replica {} due to execute_merges_on_single_replica_time_threshold",
                entry.new_part_name, replica_to_execute_merge.value());
            return false;
        }
    }
    DataPartsVector parts;
    for (const String & source_part_name : entry.source_parts)
    {
        DataPartPtr source_part_or_covering = getActiveContainingPart(source_part_name);
        if (!source_part_or_covering)
        {
            
            LOG_DEBUG(log, "Don't have all parts for merge {}; will try to fetch it instead", entry.new_part_name);
            return false;
        }
        if (source_part_or_covering->name != source_part_name)
        {
            
            
            
            
            
            constexpr const char * message = "Part {} is covered by {} but should be merged into {}. This shouldn't happen often.";
            LOG_WARNING(log, message, source_part_name, source_part_or_covering->name, entry.new_part_name);