Reducers

• Lets build a graph which will have parallel nodes
  
• In the above graph, both B and C Execute at same time in parallel
• When we change state in parallel, Invalid Update Error is shown, to resolve this we can implement reducers
• Langgraph has inbuilt reducer add_messages to add message during nodes
• Langgraph also has MessageState which uses add_messages reducer.
• But this will add too many message if used continuously increasing the token count and therefore the cost.
• To reduce the cost, we have 2 popular approaches
  • trim messages: maintain previous n messages rather than all
  • summarize messages
• Refer Here for jupyter notebook.