langgraph-persistence

import { MemorySaver, StateGraph, StateSchema, MessagesValue, START, END } from "@langchain/langgraph";
import { HumanMessage } from "@langchain/core/messages";
 
const State = new StateSchema({ messages: MessagesValue });
 
const addMessage = async (state: typeof State.State) => {
  return { messages: [{ role: "assistant", content: "Bot response" }] };
};
 
const checkpointer = new MemorySaver();
 
const graph = new StateGraph(State)
  .addNode("respond", addMessage)
  .addEdge(START, "respond")
  .addEdge("respond", END)
  .compile({ checkpointer });
 
// ALWAYS provide thread_id
const config = { configurable: { thread_id: "conversation-1" } };
 
const result1 = await graph.invoke({ messages: [new HumanMessage("Hello")] }, config);
console.log(result1.messages.length);  // 2
 
const result2 = await graph.invoke({ messages: [new HumanMessage("How are you?")] }, config);
console.log(result2.messages.length);  // 4 (previous + new)

import os
from langgraph.checkpoint.postgres import PostgresSaver
 
# Run once during deployment (not at application startup):
#   PostgresSaver.from_conn_string(os.environ["DATABASE_URL"]).setup()
 
with PostgresSaver.from_conn_string(os.environ["DATABASE_URL"]) as checkpointer:
    graph = builder.compile(checkpointer=checkpointer)

import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";
 
// Run once during deployment (not at application startup):
//   await PostgresSaver.fromConnString(process.env.DATABASE_URL!).setup();
 
const checkpointer = PostgresSaver.fromConnString(process.env.DATABASE_URL!);
const graph = builder.compile({ checkpointer });

# Different threads maintain separate state
alice_config = {"configurable": {"thread_id": "user-alice"}}
bob_config = {"configurable": {"thread_id": "user-bob"}}
 
graph.invoke({"messages": ["Hi from Alice"]}, alice_config)
graph.invoke({"messages": ["Hi from Bob"]}, bob_config)
 
# Alice's state is isolated from Bob's

// Different threads maintain separate state
const aliceConfig = { configurable: { thread_id: "user-alice" } };
const bobConfig = { configurable: { thread_id: "user-bob" } };
 
await graph.invoke({ messages: [new HumanMessage("Hi from Alice")] }, aliceConfig);
await graph.invoke({ messages: [new HumanMessage("Hi from Bob")] }, bobConfig);
 
// Alice's state is isolated from Bob's

config = {"configurable": {"thread_id": "session-1"}}
 
result = graph.invoke({"messages": ["start"]}, config)
 
# Browse checkpoint history
states = list(graph.get_state_history(config))
 
# Replay from a past checkpoint
past = states[-2]
result = graph.invoke(None, past.config)  # None = resume from checkpoint
 
# Or fork: update state at a past checkpoint, then resume
fork_config = graph.update_state(past.config, {"messages": ["edited"]})
result = graph.invoke(None, fork_config)

const config = { configurable: { thread_id: "session-1" } };
 
const result = await graph.invoke({ messages: ["start"] }, config);
 
// Browse checkpoint history (async iterable, collect to array)
const states: Awaited<ReturnType<typeof graph.getState>>[] = [];
for await (const state of graph.getStateHistory(config)) {
  states.push(state);
}
 
// Replay from a past checkpoint
const past = states[states.length - 2];
const replayed = await graph.invoke(null, past.config);  // null = resume from checkpoint
 
// Or fork: update state at a past checkpoint, then resume
const forkConfig = await graph.updateState(past.config, { messages: ["edited"] });
const forked = await graph.invoke(null, forkConfig);

config = {"configurable": {"thread_id": "session-1"}}
 
# Modify state before resuming
graph.update_state(config, {"data": "manually_updated"})
 
# Resume with updated state
result = graph.invoke(None, config)

const config = { configurable: { thread_id: "session-1" } };
 
// Modify state before resuming
await graph.updateState(config, { data: "manually_updated" });
 
// Resume with updated state
const result = await graph.invoke(null, config);

# No interrupts needed — opt out of checkpointing
subgraph = subgraph_builder.compile(checkpointer=False)
 
# Need interrupts but not cross-invocation persistence (default)
subgraph = subgraph_builder.compile()
 
# Need cross-invocation persistence (stateful)
subgraph = subgraph_builder.compile(checkpointer=True)

// No interrupts needed — opt out of checkpointing
const subgraph = subgraphBuilder.compile({ checkpointer: false });
 
// Need interrupts but not cross-invocation persistence (default)
const subgraph = subgraphBuilder.compile();
 
// Need cross-invocation persistence (stateful)
const subgraph = subgraphBuilder.compile({ checkpointer: true });

from langgraph.graph import MessagesState, StateGraph
 
def create_sub_agent(model, *, name, **kwargs):
    """Wrap an agent with a unique node name for namespace isolation."""
    agent = create_agent(model=model, name=name, **kwargs)
    return (
        StateGraph(MessagesState)
        .add_node(name, agent)  # unique name -> stable namespace
        .add_edge("__start__", name)
        .compile()
    )
 
fruit_agent = create_sub_agent(
    "gpt-4.1-mini", name="fruit_agent",
    tools=[fruit_info], prompt="...", checkpointer=True,
)
veggie_agent = create_sub_agent(
    "gpt-4.1-mini", name="veggie_agent",
    tools=[veggie_info], prompt="...", checkpointer=True,
)

import { StateGraph, StateSchema, MessagesValue, START } from "@langchain/langgraph";
 
function createSubAgent(model: string, { name, ...kwargs }: { name: string; [key: string]: any }) {
  const agent = createAgent({ model, name, ...kwargs });
  return new StateGraph(new StateSchema({ messages: MessagesValue }))
    .addNode(name, agent)  // unique name -> stable namespace
    .addEdge(START, name)
    .compile();
}
 
const fruitAgent = createSubAgent("gpt-4.1-mini", {
  name: "fruit_agent", tools: [fruitInfo], prompt: "...", checkpointer: true,
});
const veggieAgent = createSubAgent("gpt-4.1-mini", {
  name: "veggie_agent", tools: [veggieInfo], prompt: "...", checkpointer: true,
});

from langgraph.store.memory import InMemoryStore
 
store = InMemoryStore()
 
# Save user preference (available across ALL threads)
store.put(("alice", "preferences"), "language", {"preference": "short responses"})
 
# Node with store — access via runtime
from langgraph.runtime import Runtime
 
def respond(state, runtime: Runtime):
    prefs = runtime.store.get((state["user_id"], "preferences"), "language")
    return {"response": f"Using preference: {prefs.value}"}
 
# Compile with BOTH checkpointer and store
graph = builder.compile(checkpointer=checkpointer, store=store)
 
# Both threads access same long-term memory
graph.invoke({"user_id": "alice"}, {"configurable": {"thread_id": "thread-1"}})
graph.invoke({"user_id": "alice"}, {"configurable": {"thread_id": "thread-2"}})  # Same preferences!

import { MemoryStore } from "@langchain/langgraph";
 
const store = new MemoryStore();
 
// Save user preference (available across ALL threads)
await store.put(["alice", "preferences"], "language", { preference: "short responses" });
 
// Node with store — access via runtime
const respond = async (state: typeof State.State, runtime: any) => {
  const item = await runtime.store?.get(["alice", "preferences"], "language");
  return { response: `Using preference: ${item?.value?.preference}` };
};
 
// Compile with BOTH checkpointer and store
const graph = builder.compile({ checkpointer, store });
 
// Both threads access same long-term memory
await graph.invoke({ userId: "alice" }, { configurable: { thread_id: "thread-1" } });
await graph.invoke({ userId: "alice" }, { configurable: { thread_id: "thread-2" } });  // Same preferences!

from langgraph.store.memory import InMemoryStore
 
store = InMemoryStore()
 
store.put(("user-123", "facts"), "location", {"city": "San Francisco"})  # Put
item = store.get(("user-123", "facts"), "location")  # Get
results = store.search(("user-123", "facts"), filter={"city": "San Francisco"})  # Search
store.delete(("user-123", "facts"), "location")  # Delete

# WRONG: No thread_id - state NOT persisted!
graph.invoke({"messages": ["Hello"]})
graph.invoke({"messages": ["What did I say?"]})  # Doesn't remember!
 
# CORRECT: Always provide thread_id
config = {"configurable": {"thread_id": "session-1"}}
graph.invoke({"messages": ["Hello"]}, config)
graph.invoke({"messages": ["What did I say?"]}, config)  # Remembers!

// WRONG: No thread_id - state NOT persisted!
await graph.invoke({ messages: [new HumanMessage("Hello")] });
await graph.invoke({ messages: [new HumanMessage("What did I say?")] });  // Doesn't remember!
 
// CORRECT: Always provide thread_id
const config = { configurable: { thread_id: "session-1" } };
await graph.invoke({ messages: [new HumanMessage("Hello")] }, config);
await graph.invoke({ messages: [new HumanMessage("What did I say?")] }, config);  // Remembers!

# WRONG: Data lost on process restart
checkpointer = InMemorySaver()  # In-memory only!
 
# CORRECT: Use persistent storage for production
from langgraph.checkpoint.postgres import PostgresSaver
with PostgresSaver.from_conn_string("postgresql://...") as checkpointer:
    checkpointer.setup()  # only needed on first use to create tables
    graph = builder.compile(checkpointer=checkpointer)

// WRONG: Data lost on process restart
const checkpointer = new MemorySaver();  // In-memory only!
 
// CORRECT: Use persistent storage for production
import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";
const checkpointer = PostgresSaver.fromConnString("postgresql://...");
await checkpointer.setup(); // only needed on first use to create tables

from langgraph.types import Overwrite
 
# State with reducer: items: Annotated[list, operator.add]
# Current state: {"items": ["A", "B"]}
 
# update_state PASSES THROUGH reducers
graph.update_state(config, {"items": ["C"]})  # Result: ["A", "B", "C"] - Appended!
 
# To REPLACE instead, use Overwrite
graph.update_state(config, {"items": Overwrite(["C"])})  # Result: ["C"] - Replaced

import { Overwrite } from "@langchain/langgraph";
 
// State with reducer: items uses concat reducer
// Current state: { items: ["A", "B"] }
 
// updateState PASSES THROUGH reducers
await graph.updateState(config, { items: ["C"] });  // Result: ["A", "B", "C"] - Appended!
 
// To REPLACE instead, use Overwrite
await graph.updateState(config, { items: new Overwrite(["C"]) });  // Result: ["C"] - Replaced

# WRONG: Store not available in node
def my_node(state):
    store.put(...)  # NameError! store not defined
 
# CORRECT: Access store via runtime
from langgraph.runtime import Runtime
 
def my_node(state, runtime: Runtime):
    runtime.store.put(...)  # Correct store instance

// WRONG: Store not available in node
const myNode = async (state) => {
  store.put(...);  // ReferenceError!
};
 
// CORRECT: Access store via runtime
const myNode = async (state, runtime) => {
  await runtime.store?.put(...);  // Correct store instance
};