**Use case**

Currently, `system.replicas` table has `total_replicas` and `active_replicas` columns which are useful to check/alert when some replicas are down. One problem, these columns are numbers. They tell when there is a problem, but you need to further check ZooKeeper or query all the nodes to detect what exact replicas (hosts) are down/inactive/have problems.

**Describe the solution you'd like**

Add a replicas column maybe as a map which would contain the replica name, and it's status. Or, add 2 array columns with `replica_names` and `active_replica_names`

**Alternative**

Something along the line

```sql
select path, value from system.zookeeper where path IN (
    select concat(path, '/', name) from system.zookeeper where path in (select concat(zookeeper_path, '/replicas') from system.replicas)
)
and name = 'is_active'
```
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);
            if (!source_part_or_covering->info.contains(MergeTreePartInfo::fromPartName(entry.new_part_name, format_version)))
                throw Exception(ErrorCodes::LOGICAL_ERROR, message, source_part_name, source_part_or_covering->name, entry.new_part_name);
            return false;
        }
        parts.push_back(source_part_or_covering);
    }
    
    if (entry.create_time + storage_settings_ptr->prefer_fetch_merged_part_time_threshold.totalSeconds() <= time(nullptr))
    {
        
        
        size_t sum_parts_bytes_on_disk = 0;
        for (const auto & part : parts)
            sum_parts_bytes_on_disk += part->getBytesOnDisk();
        if (sum_parts_bytes_on_disk >= storage_settings_ptr->prefer_fetch_merged_part_size_threshold)
        {
            String replica = findReplicaHavingPart(entry.new_part_name, true);    
            if (!replica.empty())
            {
                LOG_DEBUG(log, "Prefer to fetch {} from replica {}", entry.new_part_name, replica);
                return false;
            }
        }
    }
    
    size_t estimated_space_for_merge = MergeTreeDataMergerMutator::estimateNeededDiskSpace(parts);