**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'
```
*/
    unsigned try_no = 0;
    Strings missing_parts;
    do
    {
        if (try_no)
            LOG_INFO(log, "Some of parts ({}) are missing. Will try to fetch covering parts.", missing_parts.size());
        if (try_no >= query_context->getSettings().max_fetch_partition_retries_count)
            throw Exception("Too many retries to fetch parts from " + best_replica_path, ErrorCodes::TOO_MANY_RETRIES_TO_FETCH_PARTS);
        Strings parts = zookeeper->getChildren(fs::path(best_replica_path) / "parts");
        ActiveDataPartSet active_parts_set(format_version, parts);
        Strings parts_to_fetch;
        if (missing_parts.empty())
        {
            parts_to_fetch = active_parts_set.getParts();
            
            Strings parts_to_fetch_partition;
            for (const String & part : parts_to_fetch)
            {
                if (MergeTreePartInfo::fromPartName(part, format_version).partition_id == partition_id)
                    parts_to_fetch_partition.push_back(part);
            }
            parts_to_fetch = std::move(parts_to_fetch_partition);
            if (parts_to_fetch.empty())
                throw Exception("Partition " + partition_id + " on " + best_replica_path + " doesn't exist", ErrorCodes::PARTITION_DOESNT_EXIST);
        }
        else
        {
            for (const String & missing_part : missing_parts)
            {