Stores - Docs by LangChain

Stores let agents persist information across threads, including user preferences, accumulated knowledge, and facts that should survive beyond a single conversation. Unlike checkpointers, which save the full graph state scoped to one thread, stores hold arbitrary key-value data accessible from any thread.

Agent Server handles stores automatically When using the Agent Server, you do not need to implement or configure stores manually. The API handles all storage infrastructure for you behind the scenes.

InMemoryStore is suitable for development and testing. For production, use a persistent store like PostgresStore, MongoDBStore, or RedisStore. All implementations extend BaseStore, which is the type annotation to use in node function signatures.

Basic usage

The following code snippet shows the InMemoryStore in isolation without using LangGraph:

from langgraph.store.memory import InMemoryStore
store = InMemoryStore()

Memories are namespaced by a tuple, which is (<user_id>, "memories") in the following example. The namespace can be any length and represent anything, does not have to be user specific.

user_id = "1"
namespace_for_memory = (user_id, "memories")

Use the store.put method to save memories to the namespace in the store. Specify the namespace, as defined above, and a key-value pair for the memory: the key is simply a unique identifier for the memory (memory_id) and the value (a dictionary) is the memory itself.

memory_id = str(uuid.uuid4())
memory = {"food_preference" : "I like pizza"}
store.put(namespace_for_memory, memory_id, memory)

Read out memories from your namespace using the store.search method, which returns memories for a given user as a list, up to the limit argument (default 10). With InMemoryStore, items are returned in insertion order, so the most recent memory is last in the list; other backends may order memories differently (see Listing items in a namespace).

memories = store.search(namespace_for_memory)
memories[-1].dict()
{'value': {'food_preference': 'I like pizza'},
 'key': '07e0caf4-1631-47b7-b15f-65515d4c1843',
 'namespace': ['1', 'memories'],
 'created_at': '2024-10-02T17:22:31.590602+00:00',
 'updated_at': '2024-10-02T17:22:31.590605+00:00'}

Each memory type is a Python class (Item) with certain attributes. We can access it as a dictionary by converting with .dict. The attributes it has are:

value: The value (itself a dictionary) of this memory
key: A unique key for this memory in this namespace
namespace: A tuple of strings, the namespace of this memory type
While the type is tuple[str, ...], it may be serialized as a list when converted to JSON (for example, ['1', 'memories']).
created_at: Timestamp for when this memory was created
updated_at: Timestamp for when this memory was updated

Listing items in a namespace

Calling store.search (or the async store.asearch) with no query and no filter returns the items stored under namespace_prefix, up to limit. Use this to enumerate everything in a namespace when you don’t need semantic ranking.

# Return up to 100 items stored under ("alice", "memories").
items = store.search(("alice", "memories"), limit=100)

Three behaviors to keep in mind:

namespace_prefix matches by prefix, not exactly. ("alice",) also returns items under ("alice", "memories"), ("alice", "preferences"), and so on. To restrict to a single level, pass the full namespace or filter the returned items client-side on item.namespace.
Results past limit are silently truncated. There is no overflow signal—set limit above your expected maximum, or paginate with offset.
Default ordering depends on the store backend. PostgresStore and AsyncPostgresStore return results ordered by updated_at descending (most recently updated first). InMemoryStore returns results in insertion order (most recently inserted last). Do not rely on a specific order across implementations; sort client-side on item.updated_at if order matters.

To page through a large namespace:

page_size = 50
offset = 0
while True:
    page = store.search(("alice", "memories"), limit=page_size, offset=offset)
    if not page:
        break
    for item in page:
        pass
    offset += page_size

To discover which namespaces exist (for example, to iterate over every user before listing their memories), use store.list_namespaces or store.alist_namespaces:

# All namespaces that start with ("alice",), truncated to two levels deep.
namespaces = store.list_namespaces(prefix=("alice",), max_depth=2)

Semantic search

Beyond simple retrieval, the store also supports semantic search, allowing you to find memories based on meaning rather than exact matches. To enable this, configure the store with an embedding model:

from langchain.embeddings import init_embeddings

store = InMemoryStore(
    index={
        "embed": init_embeddings("openai:text-embedding-3-small"),  # Embedding provider
        "dims": 1536,                              # Embedding dimensions
        "fields": ["food_preference", "$"]              # Fields to embed
    }
)

Now when searching, you can use natural language queries to find relevant memories:

# Find memories about food preferences
# (This can be done after putting memories into the store)
memories = store.search(
    namespace_for_memory,
    query="What does the user like to eat?",
    limit=3  # Return top 3 matches
)

You can control which parts of your memories get embedded by configuring the fields parameter or by specifying the index parameter when storing memories:

# Store with specific fields to embed
store.put(
    namespace_for_memory,
    str(uuid.uuid4()),
    {
        "food_preference": "I love Italian cuisine",
        "context": "Discussing dinner plans"
    },
    index=["food_preference"]  # Only embed "food_preferences" field
)

# Store without embedding (still retrievable, but not searchable)
store.put(
    namespace_for_memory,
    str(uuid.uuid4()),
    {"system_info": "Last updated: 2024-01-01"},
    index=False
)

Using in LangGraph

The store works hand-in-hand with the checkpointer: the checkpointer saves state to threads, as discussed above, and the store allows you to store arbitrary information for access across threads. Compile the graph with both the checkpointer and the store as follows.

from dataclasses import dataclass
from langgraph.checkpoint.memory import InMemorySaver

@dataclass
class Context:
    user_id: str

# We need this because we want to enable threads (conversations)
checkpointer = InMemorySaver()

# ... Define the graph ...

# Compile the graph with the checkpointer and store
builder = StateGraph(MessagesState, context_schema=Context)
# ... add nodes and edges ...
graph = builder.compile(checkpointer=checkpointer, store=store)

Then invoke the graph with a thread_id, as before, and also with a user_id, which serves as the namespace for memories for this particular user as before.

# Invoke the graph
config = {"configurable": {"thread_id": "1"}}

# First let's just say hi to the AI
for update in graph.stream(
    {"messages": [{"role": "user", "content": "hi"}]},
    config,
    stream_mode="updates",
    context=Context(user_id="1"),
):
    print(update)

You can access the store and the user_id from any node by using the Runtime object. The Runtime is automatically injected by LangGraph when you add it as a parameter to your node function. You can use it to save memories:

from langgraph.runtime import Runtime
from dataclasses import dataclass

@dataclass
class Context:
    user_id: str

async def update_memory(state: MessagesState, runtime: Runtime[Context]):

    # Get the user id from the runtime context
    user_id = runtime.context.user_id

    # Namespace the memory
    namespace = (user_id, "memories")

    # ... Analyze conversation and create a new memory

    # Create a new memory ID
    memory_id = str(uuid.uuid4())

    # We create a new memory
    await runtime.store.aput(namespace, memory_id, {"memory": memory})

You can also access the store from any node and use the store.search method to get memories. Memories are returned as a list of objects that can be converted to a dictionary.

memories[-1].dict()
{'value': {'food_preference': 'I like pizza'},
 'key': '07e0caf4-1631-47b7-b15f-65515d4c1843',
 'namespace': ['1', 'memories'],
 'created_at': '2024-10-02T17:22:31.590602+00:00',
 'updated_at': '2024-10-02T17:22:31.590605+00:00'}

You access the memories and use them in model calls.

from dataclasses import dataclass
from langgraph.runtime import Runtime

@dataclass
class Context:
    user_id: str

async def call_model(state: MessagesState, runtime: Runtime[Context]):
    # Get the user id from the runtime context
    user_id = runtime.context.user_id

    # Namespace the memory
    namespace = (user_id, "memories")

    # Search based on the most recent message
    memories = await runtime.store.asearch(
        namespace,
        query=state["messages"][-1].content,
        limit=3
    )
    info = "\n".join([d.value["memory"] for d in memories])

    # ... Use memories in the model call

If you create a new thread, you can still access the same memories so long as the user_id is the same.

# Invoke the graph on a new thread
config = {"configurable": {"thread_id": "2"}}

# Let's say hi again
for update in graph.stream(
    {"messages": [{"role": "user", "content": "hi, tell me about my memories"}]},
    config,
    stream_mode="updates",
    context=Context(user_id="1"),
):
    print(update)

When you use LangSmith locally (e.g., in Studio) or hosted, the base store is available to use by default and you do not need to specify it during graph compilation. To enable semantic search, however, you do need to configure the indexing settings in your langgraph.json file. For example:

{
    ...
    "store": {
        "index": {
            "embed": "openai:text-embeddings-3-small",
            "dims": 1536,
            "fields": ["$"]
        }
    }
}

See the deployment guide for more details and configuration options.

Build a custom store

To use a storage backend other than the built-in implementations, subclass BaseStore and implement its required methods. The built-in InMemoryStore is the simplest reference implementation.

Base contract

All five async methods are required. Sync counterparts (put, get, delete, search, list_namespaces) are optional but recommended for compatibility with sync graph execution.

Method	Description
`aput(namespace, key, value, index=None)`	Store or overwrite a single item
`aget(namespace, key)`	Retrieve a single item by key; return `None` if missing
`adelete(namespace, key)`	Delete a single item
`asearch(namespace_prefix, *, query=None, filter=None, limit=10, offset=0)`	Search items under a namespace prefix; optionally by semantic query
`alist_namespaces(*, prefix=None, suffix=None, max_depth=None, limit=100, offset=0)`	List namespaces matching a prefix/suffix pattern

Look up exact signatures before implementing:

import inspect
from langgraph.store.base import BaseStore
print(inspect.getsource(BaseStore))

Namespace design

Namespaces are tuples of strings, e.g. ("user_id", "memories"). Store implementations must support:

Prefix matching: asearch(("alice",)) returns items under ("alice",), ("alice", "memories"), and any other sub-namespace.
Exact key lookup: aget(("alice", "memories"), "some-key") must be O(1) or close to it.

For SQL backends, a common schema:

CREATE TABLE store_items (
    namespace   TEXT[] NOT NULL,
    key         TEXT NOT NULL,
    value       JSONB NOT NULL,
    created_at  TIMESTAMPTZ DEFAULT now(),
    updated_at  TIMESTAMPTZ DEFAULT now(),
    PRIMARY KEY (namespace, key)
);

CREATE INDEX ON store_items USING gin(namespace);

Serialization

Store values are plain Python dicts — no special serializer is required. Serialize with json.dumps / json.loads or a JSONB column directly. Do not store raw Python objects that are not JSON-serializable.

Semantic search support

If your backend supports vector search, implement the query parameter on asearch:

Accept a query: str | None argument.
When query is not None, embed it and rank results by cosine similarity.
Results should include a score field on each Item when query is provided.

If your backend does not support vector search, raise NotImplementedError when query is passed.

Testing

There is currently no conformance suite for custom stores. Test against InMemoryStore as the reference:

import pytest
from langgraph.store.memory import InMemoryStore
from your_module import YourStore

@pytest.fixture
async def store():
    async with YourStore.create() as s:
        yield s

@pytest.fixture
def reference():
    return InMemoryStore()

async def test_put_and_get(store, reference):
    ns = ("test", "ns")
    for s in [store, reference]:
        await s.aput(ns, "k1", {"val": 1})
        item = await s.aget(ns, "k1")
        assert item is not None
        assert item.value == {"val": 1}

async def test_delete(store, reference):
    ns = ("test", "ns")
    for s in [store, reference]:
        await s.aput(ns, "k1", {"val": 1})
        await s.adelete(ns, "k1")
        assert await s.aget(ns, "k1") is None

async def test_search_prefix(store, reference):
    for s in [store, reference]:
        await s.aput(("user", "memories"), "m1", {"text": "likes pizza"})
        results = await s.asearch(("user",))
        assert any(r.key == "m1" for r in results)

Next steps

Add a custom store to Agent Server — deploying your implementation
Checkpointers — thread-scoped state persistence

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​Basic usage

​Listing items in a namespace

​Semantic search

​Using in LangGraph

​Build a custom store

​Base contract

​Namespace design

​Serialization

​Semantic search support

​Testing

​Next steps

Basic usage

Listing items in a namespace

Semantic search

Using in LangGraph

Build a custom store

Base contract

Namespace design

Serialization

Semantic search support

Testing

Next steps