**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 (action_type == ActionLocks::PartsMerge)
        return merger_mutator.merges_blocker.cancel();
    if (action_type == ActionLocks::PartsTTLMerge)
        return merger_mutator.ttl_merges_blocker.cancel();
    if (action_type == ActionLocks::PartsFetch)
        return fetcher.blocker.cancel();
    if (action_type == ActionLocks::PartsSend)
    {
        auto data_parts_exchange_ptr = std::atomic_load(&data_parts_exchange_endpoint);
        return data_parts_exchange_ptr ? data_parts_exchange_ptr->blocker.cancel() : ActionLock();
    }
    if (action_type == ActionLocks::ReplicationQueue)
        return queue.actions_blocker.cancel();
    if (action_type == ActionLocks::PartsMove)
        return parts_mover.moves_blocker.cancel();
    return {};
}
void StorageReplicatedMergeTree::onActionLockRemove(StorageActionBlockType action_type)
{
    if (action_type == ActionLocks::PartsMerge || action_type == ActionLocks::PartsTTLMerge
        || action_type == ActionLocks::PartsFetch || action_type == ActionLocks::PartsSend
        || action_type == ActionLocks::ReplicationQueue)
        background_executor.triggerTask();
    else if (action_type == ActionLocks::PartsMove)
        background_moves_executor.triggerTask();
}
bool StorageReplicatedMergeTree::waitForShrinkingQueueSize(size_t queue_size, UInt64 max_wait_milliseconds)