**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'
```
{
        for (auto & index : new_metadata.secondary_indices)
            index.recalculateWithNewColumns(new_metadata.columns, getContext());
    }
    if (!metadata_diff.ttl_table_changed && new_metadata.table_ttl.definition_ast != nullptr)
        new_metadata.table_ttl = TTLTableDescription::getTTLForTableFromAST(
            new_metadata.table_ttl.definition_ast, new_metadata.columns, getContext(), new_metadata.primary_key);
    
    
    checkTTLExpressions(new_metadata, old_metadata);
    setProperties(new_metadata, old_metadata);
    auto table_id = getStorageID();
    DatabaseCatalog::instance().getDatabase(table_id.database_name)->alterTable(getContext(), table_id, new_metadata);
}
/** If necessary, restore a part, replica itself adds a record for its receipt.
  * What time should I put for this entry in the queue? Time is taken into account when calculating lag of replica.
  * For these purposes, it makes sense to use creation time of missing part
  *  (that is, in calculating lag, it will be taken into account how old is the part we need to recover).
  */
static time_t tryGetPartCreateTime(zkutil::ZooKeeperPtr & zookeeper, const String & replica_path, const String & part_name)
{
    time_t res = 0;
    
    Coordination::Stat stat;
    String unused;
    if (zookeeper->tryGet(fs::path(replica_path) / "parts" / part_name, unused, &stat))
        res = stat.ctime / 1000;
    return res;
}
void StorageReplicatedMergeTree::checkParts(bool skip_sanity_checks)