**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'
```
[[fallthrough]];
        case LogEntry::GET_PART:
            do_fetch = true;
            break;
        case LogEntry::MERGE_PARTS:
            
            
            do_fetch = !tryExecuteMerge(entry);
            break;
        case LogEntry::MUTATE_PART:
            
            do_fetch = !tryExecutePartMutation(entry);
            break;
        case LogEntry::ALTER_METADATA:
            return executeMetadataAlter(entry);
        case LogEntry::SYNC_PINNED_PART_UUIDS:
            syncPinnedPartUUIDs();
            return true;
        case LogEntry::CLONE_PART_FROM_SHARD:
            executeClonePartFromShard(entry);
            return true;
        default:
            throw Exception(ErrorCodes::LOGICAL_ERROR, "Unexpected log entry type: {}", static_cast<int>(entry.type));
    }
    if (do_fetch)
        return executeFetch(entry);
    return true;
}
bool StorageReplicatedMergeTree::tryExecuteMerge(const LogEntry & entry)