**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'
```
{
            if (interserver_scheme != address.scheme)
                throw Exception("Interserver schemes are different: '" + interserver_scheme
                    + "' != '" + address.scheme + "', can't fetch part from " + address.host,
                    ErrorCodes::INTERSERVER_SCHEME_DOESNT_MATCH);
            return fetcher.fetchPart(
                metadata_snapshot,
                getContext(),
                part_name,
                source_replica_path,
                address.host,
                address.replication_port,
                timeouts,
                credentials->getUser(),
                credentials->getPassword(),
                interserver_scheme,
                replicated_fetches_throttler,
                to_detached,
                "",
                &tagger_ptr,
                true);
        };
    }
    try
    {
        part = get_part();
        if (!to_detached)
        {
            Transaction transaction(*this);
            renameTempPartAndReplace(part, nullptr, &transaction);