**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'
```
{
        return replicated_sends_throttler;
    }
    bool createEmptyPartInsteadOfLost(zkutil::ZooKeeperPtr zookeeper, const String & lost_part_name);
private:
    std::atomic_bool are_restoring_replica {false};
    
    ReplicatedMergeTreeQuorumAddedParts::PartitionIdToMaxBlock getMaxAddedBlocks() const;
    
    void clearOldPartsAndRemoveFromZK();
    friend class ReplicatedMergeTreeSink;
    friend class ReplicatedMergeTreePartCheckThread;
    friend class ReplicatedMergeTreeCleanupThread;
    friend class ReplicatedMergeTreeAlterThread;
    friend class ReplicatedMergeTreeRestartingThread;
    friend class ReplicatedMergeTreeMergeStrategyPicker;
    friend struct ReplicatedMergeTreeLogEntry;
    friend class ScopedPartitionMergeLock;
    friend class ReplicatedMergeTreeQueue;
    friend class PartMovesBetweenShardsOrchestrator;
    friend class MergeTreeData;
    using MergeStrategyPicker = ReplicatedMergeTreeMergeStrategyPicker;
    using LogEntry = ReplicatedMergeTreeLogEntry;
    using LogEntryPtr = LogEntry::Ptr;
    using MergeTreeData::MutableDataPartPtr;
    zkutil::ZooKeeperPtr current_zookeeper;        
    mutable std::mutex current_zookeeper_mutex;