**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'
```
LOG_WARNING(log, "No active replica has part {}, "
                                         "but that part needs quorum and /quorum/status contains entry about another part {}. "
                                         "It means that part was successfully written to {} replicas, but then all of them goes offline. "
                                         "Or it is a bug.", entry.new_part_name, quorum_entry.part_name, entry.quorum);
                    }
                }
            }
            if (replica.empty())
            {
                ProfileEvents::increment(ProfileEvents::ReplicatedPartFailedFetches);
                throw Exception("No active replica has part " + entry.new_part_name + " or covering part", ErrorCodes::NO_REPLICA_HAS_PART);
            }
        }
        try
        {
            String part_name = entry.actual_new_part_name.empty() ? entry.new_part_name : entry.actual_new_part_name;
            if (!entry.actual_new_part_name.empty())
                LOG_DEBUG(log, "Will fetch part {} instead of {}", entry.actual_new_part_name, entry.new_part_name);
            if (!fetchPart(part_name, metadata_snapshot, fs::path(zookeeper_path) / "replicas" / replica, false, entry.quorum))
                return false;
        }
        catch (Exception & e)
        {
            
            if (e.code() == ErrorCodes::RECEIVED_ERROR_TOO_MANY_REQUESTS)
                e.addMessage("Too busy replica. Will try later.");
            throw;
        }
        if (entry.type == LogEntry::MERGE_PARTS)
            ProfileEvents::increment(ProfileEvents::ReplicatedPartFetchesOfMerged);