**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 (!all_in_zk)
        return CreateMergeEntryResult::MissingPart;
    ReplicatedMergeTreeLogEntryData entry;
    entry.type = LogEntry::MERGE_PARTS;
    entry.source_replica = replica_name;
    entry.new_part_name = merged_name;
    entry.new_part_uuid = merged_part_uuid;
    entry.new_part_type = merged_part_type;
    entry.merge_type = merge_type;
    entry.deduplicate = deduplicate;
    entry.deduplicate_by_columns = deduplicate_by_columns;
    entry.create_time = time(nullptr);
    for (const auto & part : parts)
        entry.source_parts.push_back(part->name);
    Coordination::Requests ops;
    Coordination::Responses responses;
    ops.emplace_back(zkutil::makeCreateRequest(
        fs::path(zookeeper_path) / "log/log-", entry.toString(),
        zkutil::CreateMode::PersistentSequential));
    ops.emplace_back(zkutil::makeSetRequest(
        fs::path(zookeeper_path) / "log", "", log_version)); 
    Coordination::Error code = zookeeper->tryMulti(ops, responses);
    if (code == Coordination::Error::ZOK)
    {
        String path_created = dynamic_cast<const Coordination::CreateResponse &>(*responses.front()).path_created;
        entry.znode_name = path_created.substr(path_created.find_last_of('/') + 1);
        ProfileEvents::increment(ProfileEvents::CreatedLogEntryForMerge);
        LOG_TRACE(log, "Created log entry {} for merge {}", path_created, merged_name);
    }