**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'
```
else if (code == Coordination::Error::ZBADVERSION)
    {
        ProfileEvents::increment(ProfileEvents::NotCreatedLogEntryForMerge);
        LOG_TRACE(log, "Log entry is not created for merge {} because log was updated", merged_name);
        return CreateMergeEntryResult::LogUpdated;
    }
    else
    {
        zkutil::KeeperMultiException::check(code, ops, responses);
    }
    if (out_log_entry)
        *out_log_entry = entry;
    return CreateMergeEntryResult::Ok;
}
StorageReplicatedMergeTree::CreateMergeEntryResult StorageReplicatedMergeTree::createLogEntryToMutatePart(
    const IMergeTreeDataPart & part, const UUID & new_part_uuid, Int64 mutation_version, int32_t alter_version, int32_t log_version)
{
    auto zookeeper = getZooKeeper();
    
    if (!zookeeper->exists(fs::path(replica_path) / "parts" / part.name))
    {
        if (part.modification_time + MAX_AGE_OF_LOCAL_PART_THAT_WASNT_ADDED_TO_ZOOKEEPER < time(nullptr))
        {
            LOG_WARNING(log, "Part {} (that was selected for mutation) with age {} seconds exists locally but not in ZooKeeper."
                " Won't mutate that part and will check it.", part.name, (time(nullptr) - part.modification_time));
            enqueuePartForCheck(part.name);
        }
        return CreateMergeEntryResult::MissingPart;
    }
    MergeTreePartInfo new_part_info = part.info;