**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'
```
{
    
    if (queue.actions_blocker.isCancelled())
        return false;
    
    ReplicatedMergeTreeQueue::SelectedEntryPtr selected_entry = selectQueueEntry();
    if (!selected_entry)
        return false;
    
    if (selected_entry->log_entry->type == LogEntry::GET_PART)
    {
        executor.execute({[this, selected_entry] () mutable
        {
            return processQueueEntry(selected_entry);
        }, PoolType::FETCH});
        return true;
    }
    else
    {
        executor.execute({[this, selected_entry] () mutable
        {
            return processQueueEntry(selected_entry);
        }, PoolType::MERGE_MUTATE});
        return true;
    }
}
bool StorageReplicatedMergeTree::canExecuteFetch(const ReplicatedMergeTreeLogEntry & entry, String & disable_reason) const