Add async support to multi-query retriever. (#10873)

Added async support to the MultiQueryRetriever class.

---------

Co-authored-by: Nuno Campos <nuno@boringbits.io>

libs/langchain/langchain/retrievers/multi_query.py

@@ -1,7 +1,11 @@
+import asyncio
 import logging
 from typing import List, Sequence
 
-from langchain.callbacks.manager import CallbackManagerForRetrieverRun
+from langchain.callbacks.manager import (
+    AsyncCallbackManagerForRetrieverRun,
+    CallbackManagerForRetrieverRun,
+)
 from langchain.chains.llm import LLMChain
 from langchain.llms.base import BaseLLM
 from langchain.output_parsers.pydantic import PydanticOutputParser
@@ -83,6 +87,64 @@ class MultiQueryRetriever(BaseRetriever):
             parser_key=parser_key,
         )
 
+    async def _aget_relevant_documents(
+        self,
+        query: str,
+        *,
+        run_manager: AsyncCallbackManagerForRetrieverRun,
+    ) -> List[Document]:
+        """Get relevant documents given a user query.
+
+        Args:
+            question: user query
+
+        Returns:
+            Unique union of relevant documents from all generated queries
+        """
+        queries = await self.agenerate_queries(query, run_manager)
+        documents = await self.aretrieve_documents(queries, run_manager)
+        return self.unique_union(documents)
+
+    async def agenerate_queries(
+        self, question: str, run_manager: AsyncCallbackManagerForRetrieverRun
+    ) -> List[str]:
+        """Generate queries based upon user input.
+
+        Args:
+            question: user query
+
+        Returns:
+            List of LLM generated queries that are similar to the user input
+        """
+        response = await self.llm_chain.acall(
+            inputs={"question": question}, callbacks=run_manager.get_child()
+        )
+        lines = getattr(response["text"], self.parser_key, [])
+        if self.verbose:
+            logger.info(f"Generated queries: {lines}")
+        return lines
+
+    async def aretrieve_documents(
+        self, queries: List[str], run_manager: AsyncCallbackManagerForRetrieverRun
+    ) -> List[Document]:
+        """Run all LLM generated queries.
+
+        Args:
+            queries: query list
+
+        Returns:
+            List of retrieved Documents
+        """
+        document_lists = await asyncio.gather(
+            *(
+                self.retriever.aget_relevant_documents(
+                    query, callbacks=run_manager.get_child()
+                )
+                for query in queries
+            )
+        )
+        return [doc for docs in document_lists for doc in docs]
+
     def _get_relevant_documents(
         self,
         query: str,