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This template provides a simple chain template showcasing the usage of LLM Caching backed by Apache Cassandra® or Astra DB through CQL.

Environment Setup

To set up your environment, you will need the following:

  • an Astra Vector Database (free tier is fine!). You need a Database Administrator token, in particular the string starting with AstraCS:...;
  • likewise, get your Database ID ready, you will have to enter it below;
  • an OpenAI API Key. (More info here, note that out-of-the-box this demo supports OpenAI unless you tinker with the code.)

Note: you can alternatively use a regular Cassandra cluster: to do so, make sure you provide the USE_CASSANDRA_CLUSTER entry as shown in .env.template and the subsequent environment variables to specify how to connect to it.


To use this package, you should first have the LangChain CLI installed:

pip install -U langchain-cli

To create a new LangChain project and install this as the only package, you can do:

langchain app new my-app --package cassandra-synonym-caching

If you want to add this to an existing project, you can just run:

langchain app add cassandra-synonym-caching

And add the following code to your file:

from cassandra_synonym_caching import chain as cassandra_synonym_caching_chain

add_routes(app, cassandra_synonym_caching_chain, path="/cassandra-synonym-caching")

(Optional) Let's now configure LangSmith. LangSmith will help us trace, monitor and debug LangChain applications. You can sign up for LangSmith here. If you don't have access, you can skip this section

export LANGCHAIN_API_KEY=<your-api-key>
export LANGCHAIN_PROJECT=<your-project> # if not specified, defaults to "default"

If you are inside this directory, then you can spin up a LangServe instance directly by:

langchain serve

This will start the FastAPI app with a server is running locally at http://localhost:8000

We can see all templates at We can access the playground at

We can access the template from code with:

from langserve.client import RemoteRunnable

runnable = RemoteRunnable("http://localhost:8000/cassandra-synonym-caching")


Stand-alone LangServe template repo: here.

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