PostgreSQL also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance.
This notebook goes over how to use Postgres to store chat message history. 
from langchain_community.chat_message_histories import (
    PostgresChatMessageHistory,
)

history = PostgresChatMessageHistory(
    connection_string="postgresql://postgres:mypassword@localhost/chat_history",
    session_id="foo",
)

history.add_user_message("hi!")

history.add_ai_message("whats up?")

history.messages