**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'
```
std::unordered_set<String> partition_ids;
            for (const DataPartPtr & part : data_parts)
                partition_ids.emplace(part->info.partition_id);
            UInt64 disk_space = getStoragePolicy()->getMaxUnreservedFreeSpace();
            for (const String & partition_id : partition_ids)
            {
                size_t try_no = 0;
                for (; try_no < max_retries; ++try_no)
                {
                    
                    
                    std::lock_guard merge_selecting_lock(merge_selecting_mutex);
                    ReplicatedMergeTreeMergePredicate can_merge = queue.getMergePredicate(zookeeper);
                    FutureMergedMutatedPart future_merged_part;
                    if (storage_settings.get()->assign_part_uuids)
                        future_merged_part.uuid = UUIDHelpers::generateV4();
                    SelectPartsDecision select_decision = merger_mutator.selectAllPartsToMergeWithinPartition(
                        future_merged_part, disk_space, can_merge, partition_id, true, metadata_snapshot, nullptr, query_context->getSettingsRef().optimize_skip_merged_partitions);
                    if (select_decision != SelectPartsDecision::SELECTED)
                        break;
                    ReplicatedMergeTreeLogEntryData merge_entry;
                    CreateMergeEntryResult create_result = createLogEntryToMergeParts(
                        zookeeper, future_merged_part.parts,
                        future_merged_part.name, future_merged_part.uuid, future_merged_part.type,
                        deduplicate, deduplicate_by_columns,
                        &merge_entry, can_merge.getVersion(), future_merged_part.merge_type);
                    if (create_result == CreateMergeEntryResult::MissingPart)
                        return handle_noop("Can't create merge queue node in ZooKeeper, because some parts are missing");
                    if (create_result == CreateMergeEntryResult::LogUpdated)
                        continue;