**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'
```
merge_entries.push_back(std::move(merge_entry));
                    break;
                }
                if (try_no == max_retries)
                    return handle_noop("Can't create merge queue node in ZooKeeper, because log was updated in every of "
                        + toString(max_retries) + " tries");
            }
        }
        else
        {
            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();
                String disable_reason;
                SelectPartsDecision select_decision = SelectPartsDecision::CANNOT_SELECT;
                if (!partition)
                {
                    select_decision = merger_mutator.selectPartsToMerge(
                        future_merged_part, true, storage_settings_ptr->max_bytes_to_merge_at_max_space_in_pool, can_merge, false, &disable_reason);
                }
                else
                {
                    UInt64 disk_space = getStoragePolicy()->getMaxUnreservedFreeSpace();
                    String partition_id = getPartitionIDFromQuery(partition, query_context);
                    select_decision = merger_mutator.selectAllPartsToMergeWithinPartition(