When I’m using Graph to build a graph, I want to execute two decision processes at the same time, like calling a large model to check the weather and another large model to check locations. I set up two large model decision nodes separately, and each of them can call their respective tool nodes, wit…

hi @Huimin-station despite some issues described below, your graph decomposition (separate model/tool/route nodes) is a strong start, and your questions show you’re debugging at the right level. The issues I found are very common in early agent workflows - you’re on a solid track bro …

hi @Huimin-station hmm you’re very likely hitting a state merge conflict on the same key in the same superstep.. In LangGraph, parallel branches can run in one step, and if both branches write to one state key that has default semantics, that key behaves like “last write wins / single value per st…

Hello, first of all, thank you for your reply. I often see your comments. Regarding the problem I encountered, since I am a beginner, I might make some basic mistakes. I have a global state that contains a list of Messages [accumulating]. My decision node will send a tool call (tool_call) to add to …

Can’t parallel steps modify the same state key? Do they each need a separate key? In the end, is the data unified through a join or merge? Previously, I was just accumulating messages.

[image] Huimin-station: Hello, first of all, thank you for your reply. I often see your comments. Regarding the problem I encountered, since I am a beginner, I might make some basic mistakes. I have a global state that contains a list of Messages [accumulating]. My decision node will send a tool…

First of all, I want to express again that it is an honor to receive your guidance. I would be very grateful if you could help me check the code for errors. Here is the link to my repository: GitHub - Huimin-station/Graph-test: It's a test project about the langgraph . Since I am from China, there m…

[image] Huimin-station: Can’t parallel steps modify the same state key? Do they each need a separate key? In the end, is the data unified through a join or merge? Previously, I was just accumulating messages. Can parallel steps modify the same state key? Yes, if the key is reducer-annotate…

alright, let me inspect that codebase. Will get back to you soon :slight_smile:

First of all, thank you for carefully reviewing my messy code—this is likely due to the fact that I’m still a beginner. I also appreciate the standardized guidance you’ve provided; I’ve gained a great deal from it. Additionally, due to the time difference, it’s time for me to rest, so please forgive…

[image] Huimin-station: Could this be the reason why my parallel calls failed? My pleasure @Huimin-station :slight_smile: Sleep well! Could this be the reason why my parallel calls failed? imho, very likely yes - at least one major reason. Check it. The combination of: full-state retu…

Hello there! It’s another wonderful day. Thank you so much for your guidance yesterday. I’ve optimized my code accordingly and also implemented parallel processing.:partying_face: [fa78bdfa-568f-4cb0-bcfb-fc5f18e7f41f] This is my previous flowchart: [16b60b63-1224-418d-8dc1-8048f02425b4] This i…

Seeking help with some merge message issues when LangGraph is called in parallel

OSS Product Help LangGraph

pawel-twardziak February 26, 2026, 8:53am 13

hi there @Huimin-station

yep, sunny day today happy the optimization works!

let me go through your last message and I’ll get back to you soonish

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Seeking help with some merge message issues when LangGraph is called in parallel

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