**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, "Metadata version ({}) on replica is not up to date with metadata ({}) on source replica {}",
                metadata_version, source_metadata_version, source_replica);
    String source_metadata;
    String source_columns;
    while (true)
    {
        Coordination::Stat metadata_stat;
        Coordination::Stat columns_stat;
        source_metadata = zookeeper->get(source_path + "/metadata", &metadata_stat);
        source_columns = zookeeper->get(source_path + "/columns", &columns_stat);
        Coordination::Requests ops;
        Coordination::Responses responses;
        ops.emplace_back(zkutil::makeCheckRequest(source_path + "/metadata", metadata_stat.version));
        ops.emplace_back(zkutil::makeCheckRequest(source_path + "/columns", columns_stat.version));
        Coordination::Error code = zookeeper->tryMulti(ops, responses);
        if (code == Coordination::Error::ZOK)
            break;
        else if (code == Coordination::Error::ZBADVERSION)
            LOG_WARNING(log, "Metadata of replica {} was changed", source_path);
        else
            zkutil::KeeperMultiException::check(code, ops, responses);
    }
    ReplicatedMergeTreeLogEntryData dummy_alter;
    dummy_alter.type = LogEntry::ALTER_METADATA;
    dummy_alter.source_replica = source_replica;