src/transformers/models/rag/retrieval_rag.py/Index/init_index
class Index:    def init_index(self):
        """
        A function responsible for loading the index into memory. Should be called only once per training run of a RAG
        model. E.g. if the model is trained on multiple GPUs in a distributed setup, only one of the workers will load
        the index.
        """
        raise NotImplementedError