Alternative to using in-memory collection

When I load from an index with
`model = RAGMultiModalModel.from_index(index_path=index_name)`
then I get the following message

> You are using in-memory collection. This means every image is stored in memory.
> You might want to rethink this if you have a large collection!

I am not sure what the alternative is to using in-memory collection. I browsed the source files without finding anything.

Is there a way to use a database or any other persistent storage?

Thanks,
Carsten