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. 

{
    return config.getString("default_replica_path", "/clickhouse/tables/{uuid}/{shard}");
}
String StorageReplicatedMergeTree::getDefaultReplicaName(const Poco::Util::AbstractConfiguration & config)
{
    return config.getString("default_replica_name", "{replica}");
}
bool StorageReplicatedMergeTree::checkFixedGranularityInZookeeper()
{
    auto zookeeper = getZooKeeper();
    String metadata_str = zookeeper->get(zookeeper_path + "/metadata");
    auto metadata_from_zk = ReplicatedMergeTreeTableMetadata::parse(metadata_str);
    return metadata_from_zk.index_granularity_bytes == 0;
}
void StorageReplicatedMergeTree::waitMutationToFinishOnReplicas(