**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'
```
res_columns[col_num++]->insert(status.queue.part_mutations_in_queue);
        res_columns[col_num++]->insert(status.queue.queue_oldest_time);
        res_columns[col_num++]->insert(status.queue.inserts_oldest_time);
        res_columns[col_num++]->insert(status.queue.merges_oldest_time);
        res_columns[col_num++]->insert(status.queue.part_mutations_oldest_time);
        res_columns[col_num++]->insert(status.queue.oldest_part_to_get);
        res_columns[col_num++]->insert(status.queue.oldest_part_to_merge_to);
        res_columns[col_num++]->insert(status.queue.oldest_part_to_mutate_to);
        res_columns[col_num++]->insert(status.log_max_index);
        res_columns[col_num++]->insert(status.log_pointer);
        res_columns[col_num++]->insert(status.queue.last_queue_update);
        res_columns[col_num++]->insert(status.absolute_delay);
        res_columns[col_num++]->insert(status.total_replicas);
        res_columns[col_num++]->insert(status.active_replicas);
        res_columns[col_num++]->insert(status.zookeeper_exception);
    }
    Block header = metadata_snapshot->getSampleBlock();
    Columns fin_columns;
    fin_columns.reserve(res_columns.size());
    for (auto & col : res_columns)
        fin_columns.emplace_back(std::move(col));
    fin_columns[0] = std::move(col_database);
    fin_columns[1] = std::move(col_table);
    fin_columns[2] = std::move(col_engine);
    UInt64 num_rows = fin_columns.at(0)->size();
    Chunk chunk(std::move(fin_columns), num_rows);
    return Pipe(std::make_shared<SourceFromSingleChunk>(metadata_snapshot->getSampleBlock(), std::move(chunk)));
}
}