langchain/vectorstores/base.py/VectorStore/amax_marginal_relevance_search
class VectorStore:    async def amax_marginal_relevance_search(
        self,
        query: str,
        k: int = 4,
        fetch_k: int = 20,
        lambda_mult: float = 0.5,
        **kwargs: Any,
    ) -> List[Document]:
        """Return docs selected using the maximal marginal relevance."""

        # This is a temporary workaround to make the similarity search
        # asynchronous. The proper solution is to make the similarity search
        # asynchronous in the vector store implementations.
        func = partial(
            self.max_marginal_relevance_search, query, k, fetch_k, lambda_mult, **kwargs
        )
        return await asyncio.get_event_loop().run_in_executor(None, func)