**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'
```
ReplicatedMergeTreeRestartingThread restarting_thread;
    PartMovesBetweenShardsOrchestrator part_moves_between_shards_orchestrator;
    
    bool other_replicas_fixed_granularity = false;
    
    const bool allow_renaming;
    const size_t replicated_fetches_pool_size;
    
    
    ThrottlerPtr replicated_fetches_throttler;
    ThrottlerPtr replicated_sends_throttler;
    template <class Func>
    void foreachCommittedParts(Func && func, bool select_sequential_consistency) const;
    /** Creates the minimum set of nodes in ZooKeeper and create first replica.
      * Returns true if was created, false if exists.
      */
    bool createTableIfNotExists(const StorageMetadataPtr & metadata_snapshot);
    /**
     * Creates a replica in ZooKeeper and adds to the queue all that it takes to catch up with the rest of the replicas.
     */
    void createReplica(const StorageMetadataPtr & metadata_snapshot);
    /** Create nodes in the ZK, which must always be, but which might not exist when older versions of the server are running.
      */
    void createNewZooKeeperNodes();
    void checkTableStructure(const String & zookeeper_prefix, const StorageMetadataPtr & metadata_snapshot);
    
    
    void setTableStructure(ColumnsDescription new_columns, const ReplicatedMergeTreeTableMetadata::Diff & metadata_diff);
    /** Check that the set of parts corresponds to that in ZK (/replicas/me/parts/).