thread_id too long for Postgres checkpoint

[Freezaa9]

Checked other resources

• This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
• I added a clear and detailed title that summarizes the issue.
• I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example).
• I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue.

Example Code

from langgraph.checkpoint.postgres import PostgresSaver

DB_URI = "postgresql://postgres:postgres@localhost:5442/postgres?sslmode=disable"
with PostgresSaver.from_conn_string(DB_URI) as checkpointer:
    builder = StateGraph(...)
    graph = builder.compile(checkpointer=checkpointer)

too_long_thread_id = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"

graph.invoke(
    {"messages": [{"role": "user", "content": "hi! i am Bob"}]},
    {"configurable": {"thread_id": too_long_thread_id }},
)

Error Message and Stack Trace (if applicable)

Postgres error:
there is no unique or exclusion constraint matching the ON CONFLICT specification

Description

When a thread id is absurdly long, Posgres fail to manage the thread_id index.
When this happens, all calls (even when the thread_id is short) can fail.

System Info

python -m langchain_core.sys_info

Solution

Constrain the size of the thread_id ?

[rkarmaka98]

Would implementing a hash function be suitable as shortening the size might result in collision in same thread id?

[Freezaa9]

It could fix the issue, but then you won't have the same thread id in PostgreSQL and complicate the ease of checkpointing usage and debugging

[rkarmaka98]

@Freezaa9 we can use a uuid that will always create the same value based on phrase. Can you explain how pgsql uses this threadid or generates it?

[Freezaa9]

Update regarding the error returned by langgraph:

ProgramLimitExceeded: Index row size 4664 exceeds btree version 4 maximum 2704 for index "checkpoint_blobs_pkey" ...

_exit_ (/usr/local/lib/python3.12/site-packages/psycopgl/pipeline.py:265)

So psycopgl do return the correct error.

Would it be a good practice for langgraph to return his own error specifying that thread_id should not be that long ? Or it should solely depend on the database use for checkpointing ?

[SunHuawei]

We should add validation in LangGraph to prevent this issue. I'm thinking we could add a warning when thread_id or checkpoint_ns is too long (>500 characters?), so users can catch this before hitting the actual PostgreSQL error.

Additionally, we should update the documentation to recommend using UUID or hash for identifiers:

import uuid
thread_id = str(uuid.uuid4())  # Recommended approach

[Freezaa9]

@SunHuawei Yes I think this is the way to go.
The actual posgres limit is 2704.

So I guess we can wait for the Langgraph team to validate this approach