Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

{
    assertNotReadonly();
    if (!is_leader)
        throw Exception("DROP PARTITION cannot be done on this replica because it is not a leader", ErrorCodes::NOT_A_LEADER);
    zkutil::ZooKeeperPtr zookeeper = getZooKeeperAndAssertNotReadonly();
    const auto * partition_ast = partition->as<ASTPartition>();
    if (partition_ast && partition_ast->all)
    {
        dropAllPartitionsImpl(zookeeper, detach, query_context);
    }
    else
    {
        String partition_id = getPartitionIDFromQuery(partition, query_context);
        auto entry = dropAllPartsInPartition(*zookeeper, partition_id, query_context, detach);
        if (entry)
        {
            waitForLogEntryToBeProcessedIfNecessary(*entry, query_context);
            cleanLastPartNode(partition_id);
        }
    }
}
void StorageReplicatedMergeTree::truncate(