**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'
```
{
    LOG_TRACE(log, "Executing log entry to merge parts {} to {}",
        fmt::join(entry.source_parts, ", "), entry.new_part_name);
    const auto storage_settings_ptr = getSettings();
    if (storage_settings_ptr->always_fetch_merged_part)
    {
        LOG_INFO(log, "Will fetch part {} because setting 'always_fetch_merged_part' is true", entry.new_part_name);
        return false;
    }
    if (entry.merge_type == MergeType::TTL_RECOMPRESS &&
        (time(nullptr) - entry.create_time) <= storage_settings_ptr->try_fetch_recompressed_part_timeout.totalSeconds() &&
        entry.source_replica != replica_name)
    {
        LOG_INFO(log, "Will try to fetch part {} until '{}' because this part assigned to recompression merge. "
            "Source replica {} will try to merge this part first", entry.new_part_name,
            DateLUT::instance().timeToString(entry.create_time + storage_settings_ptr->try_fetch_recompressed_part_timeout.totalSeconds()), entry.source_replica);
        return false;
    }