Retry subgraph starting at failing node (#1695)

* Failing test

* Ensure retried subgraphs resume from current point (if any)

* Lint

* Cleanup Test

---------

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

libs/langgraph/langgraph/pregel/retry.py

@@ -4,8 +4,10 @@ import random
 import time
 from typing import Optional
 
+from langgraph.constants import CONFIG_KEY_RESUMING
 from langgraph.errors import GraphInterrupt
 from langgraph.pregel.types import PregelExecutableTask, RetryPolicy
+from langgraph.utils.config import patch_configurable
 
 logger = logging.getLogger(__name__)
 
@@ -18,12 +20,13 @@ def run_with_retry(
     retry_policy = task.retry_policy or retry_policy
     interval = retry_policy.initial_interval if retry_policy else 0
     attempts = 0
+    config = task.config
     while True:
         try:
             # clear any writes from previous attempts
             task.writes.clear()
             # run the task
-            task.proc.invoke(task.input, task.config)
+            task.proc.invoke(task.input, config)
             # if successful, end
             break
         except GraphInterrupt:
@@ -56,6 +59,8 @@ def run_with_retry(
                 f"Retrying task {task.name} after {interval:.2f} seconds (attempt {attempts}) after {exc.__class__.__name__} {exc}",
                 exc_info=exc,
             )
+            # signal subgraphs to resume (if available)
+            config = patch_configurable(config, {CONFIG_KEY_RESUMING: True})
 
 
 async def arun_with_retry(
@@ -67,16 +72,17 @@ async def arun_with_retry(
     retry_policy = task.retry_policy or retry_policy
     interval = retry_policy.initial_interval if retry_policy else 0
     attempts = 0
+    config = task.config
     while True:
         try:
             # clear any writes from previous attempts
             task.writes.clear()
             # run the task
             if stream:
-                async for _ in task.proc.astream(task.input, task.config):
+                async for _ in task.proc.astream(task.input, config):
                     pass
             else:
-                await task.proc.ainvoke(task.input, task.config)
+                await task.proc.ainvoke(task.input, config)
             # if successful, end
             break
         except GraphInterrupt:
@@ -109,3 +115,5 @@ async def arun_with_retry(
                 f"Retrying task {task.name} after {interval:.2f} seconds (attempt {attempts}) after {exc.__class__.__name__} {exc}",
                 exc_info=exc,
             )
+            # signal subgraphs to resume (if available)
+            config = patch_configurable(config, {CONFIG_KEY_RESUMING: True})

libs/langgraph/tests/test_pregel.py

@@ -11023,3 +11023,56 @@ def test_xray_issue(snapshot: SnapshotAssertion) -> None:
     app = parent.compile()
 
     assert app.get_graph(xray=True).draw_mermaid() == snapshot
+
+
+def test_subgraph_retries():
+    class State(TypedDict):
+        count: int
+
+    class ChildState(State):
+        some_list: Annotated[list, operator.add]
+
+    called_times = 0
+
+    class RandomError(ValueError):
+        """This will be retried on."""
+
+    def parent_node(state: State):
+        return {"count": state["count"] + 1}
+
+    def child_node_a(state: ChildState):
+        nonlocal called_times
+        # We want it to retry only on node_b
+        # NOT re-compute the whole graph.
+        assert not called_times
+        called_times += 1
+        return {"some_list": ["val"]}
+
+    def child_node_b(state: ChildState):
+        raise RandomError("First attempt fails")
+
+    child = StateGraph(ChildState)
+    child.add_node(child_node_a)
+    child.add_node(child_node_b)
+    child.add_edge("__start__", "child_node_a")
+    child.add_edge("child_node_a", "child_node_b")
+
+    parent = StateGraph(State)
+    parent.add_node("parent_node", parent_node)
+    parent.add_node(
+        "child_graph",
+        child.compile(),
+        retry=RetryPolicy(
+            max_attempts=3,
+            retry_on=(RandomError,),
+            backoff_factor=0.0001,
+            initial_interval=0.0001,
+        ),
+    )
+    parent.add_edge("parent_node", "child_graph")
+    parent.set_entry_point("parent_node")
+
+    checkpointer = MemorySaver()
+    app = parent.compile(checkpointer=checkpointer)
+    with pytest.raises(RandomError):
+        app.invoke({"count": 0}, {"configurable": {"thread_id": "foo"}})