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How to add node retry policies

Prerequisites

This guide assumes familiarity with the following:

There are many use cases where you may wish for your node to have a custom retry policy, for example if you are calling an API, querying a database, or calling an LLM, etc.

Setup

First, let's install the required packages and set our API keys

%%capture --no-stderr
%pip install -U langgraph langchain_anthropic langchain_community

import getpass
import os


def _set_env(var: str):
    if not os.environ.get(var):
        os.environ[var] = getpass.getpass(f"{var}: ")


_set_env("ANTHROPIC_API_KEY")

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In order to configure the retry policy, you have to pass the retry parameter to the add_node. The retry parameter takes in a RetryPolicy named tuple object. Below we instantiate a RetryPolicy object with the default parameters:

from langgraph.pregel import RetryPolicy

RetryPolicy()

RetryPolicy(initial_interval=0.5, backoff_factor=2.0, max_interval=128.0, max_attempts=3, jitter=True, retry_on=<function default_retry_on at 0x78b964b89940>)

By default, the retry_on parameter uses the default_retry_on function, which retries on any exception except for the following:

  • ValueError
  • TypeError
  • ArithmeticError
  • ImportError
  • LookupError
  • NameError
  • SyntaxError
  • RuntimeError
  • ReferenceError
  • StopIteration
  • StopAsyncIteration
  • OSError

In addition, for exceptions from popular http request libraries such as requests and httpx it only retries on 5xx status codes.

Passing a retry policy to a node

Lastly, we can pass RetryPolicy objects when we call the add_node function. In the example below we pass two different retry policies to each of our nodes:

import operator
import sqlite3
from typing import Annotated, Sequence
from typing_extensions import TypedDict

from langchain_anthropic import ChatAnthropic
from langchain_core.messages import BaseMessage

from langgraph.graph import END, StateGraph, START
from langchain_community.utilities import SQLDatabase
from langchain_core.messages import AIMessage

db = SQLDatabase.from_uri("sqlite:///:memory:")

model = ChatAnthropic(model_name="claude-2.1")


class AgentState(TypedDict):
    messages: Annotated[Sequence[BaseMessage], operator.add]


def query_database(state):
    query_result = db.run("SELECT * FROM Artist LIMIT 10;")
    return {"messages": [AIMessage(content=query_result)]}


def call_model(state):
    response = model.invoke(state["messages"])
    return {"messages": [response]}


# Define a new graph
builder = StateGraph(AgentState)
builder.add_node(
    "query_database",
    query_database,
    retry=RetryPolicy(retry_on=sqlite3.OperationalError),
)
builder.add_node("model", call_model, retry=RetryPolicy(max_attempts=5))
builder.add_edge(START, "model")
builder.add_edge("model", "query_database")
builder.add_edge("query_database", END)

graph = builder.compile()

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