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. 

try
        {
            global_context->loadOrReloadDictionaries(config());
        }
        catch (...)
        {
            tryLogCurrentException(log, "Caught exception while loading dictionaries.");
            throw;
        }
        
        try
        {
            global_context->tryCreateEmbeddedDictionaries(config());
        }
        catch (...)
        {
            tryLogCurrentException(log, "Caught exception while loading embedded dictionaries.");
            throw;
        }
        
        try
        {
            global_context->loadOrReloadModels(config());
        }
        catch (...)
        {
            tryLogCurrentException(log, "Caught exception while loading dictionaries.");
            throw;
        }