**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'
```
CreateMergeEntryResult createLogEntryToMergeParts(
        zkutil::ZooKeeperPtr & zookeeper,
        const DataPartsVector & parts,
        const String & merged_name,
        const UUID & merged_part_uuid,
        const MergeTreeDataPartType & merged_part_type,
        bool deduplicate,
        const Names & deduplicate_by_columns,
        ReplicatedMergeTreeLogEntryData * out_log_entry,
        int32_t log_version,
        MergeType merge_type);
    CreateMergeEntryResult createLogEntryToMutatePart(
        const IMergeTreeDataPart & part,
        const UUID & new_part_uuid,
        Int64 mutation_version,
        int32_t alter_version,
        int32_t log_version);
    
    ConnectionTimeouts getFetchPartHTTPTimeouts(ContextPtr context);
    /** Returns an empty string if no one has a part.
      */
    String findReplicaHavingPart(const String & part_name, bool active);
    static String findReplicaHavingPart(const String & part_name, const String & zookeeper_path_, zkutil::ZooKeeper::Ptr zookeeper_);
    bool checkReplicaHavePart(const String & replica, const String & part_name);
    bool checkIfDetachedPartExists(const String & part_name);
    bool checkIfDetachedPartitionExists(const String & partition_name);
    /** Find replica having specified part or any part that covers it.