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Question Answering over Documents with Milvus and LangChain

This guide demonstrates how to build an LLM-driven question-answering application with Milvus and LangChain.

Before you begin

Code snippets on this page require pymilvus and langchain installed. OpenAI's embedding API has also been used to embed docs into the vector store, and therefore openai and tiktoken are also required. If they are not present on your system, run the following commands to install them.

! python -m pip install --upgrade pymilvus langchain openai tiktoken

Global parameters

In this section, you need to set up all parameters to be used in the following code snippets.

import os

# 1. Set up the name of the collection to be created.
COLLECTION_NAME = 'doc_qa_db'

# 2. Set up the dimension of the embeddings.
DIMENSION = 768

# 3. Set up the cohere api key
OPENAI_API_KEY = "YOUR_OPENAI_API_KEY"
os.environ["OPENAI_API_KEY"] = OPENAI_API_KEY

# 4. Set up the connection parameters for your Zilliz Cloud cluster.
URI = 'YOUR_CLUSTER_ENDPOINT'

# 5. Set up the token for your Zilliz Cloud cluster.
# You can either use an API key or a set of cluster username and password joined by a colon.
TOKEN = 'YOUR_CLUSTER_TOKEN'

Prepare data

Before you dive in, you should finish the following steps:

  • Prepare the documents you want the LLM to peak at when it thinks.
  • Set up an embedding model to convert documents into vector embeddings.
  • Set up a vector store used to save the vector embeddings.
from langchain.embeddings.openai import OpenAIEmbeddings
from langchain.vectorstores.zilliz import Zilliz
from langchain.document_loaders import WebBaseLoader
from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain.chat_models import ChatOpenAI
from langchain.vectorstores.milvus import Milvus
from langchain.schema.runnable import RunnablePassthrough
from langchain.prompts import PromptTemplate

# Use the WebBaseLoader to load specified web pages into documents
loader = WebBaseLoader([
    'https://milvus.io/docs/overview.md',
    'https://milvus.io/docs/release_notes.md',
    'https://milvus.io/docs/architecture_overview.md',
    'https://milvus.io/docs/four_layers.md',
    'https://milvus.io/docs/main_components.md',
    'https://milvus.io/docs/data_processing.md',
    'https://milvus.io/docs/bitset.md',
    'https://milvus.io/docs/boolean.md',
    'https://milvus.io/docs/consistency.md',
    'https://milvus.io/docs/coordinator_ha.md',
    'https://milvus.io/docs/replica.md',
    'https://milvus.io/docs/knowhere.md',
    'https://milvus.io/docs/schema.md',
    'https://milvus.io/docs/dynamic_schema.md',
    'https://milvus.io/docs/json_data_type.md',
    'https://milvus.io/docs/metric.md',
    'https://milvus.io/docs/partition_key.md',
    'https://milvus.io/docs/multi_tenancy.md',
    'https://milvus.io/docs/timestamp.md',
    'https://milvus.io/docs/users_and_roles.md',
    'https://milvus.io/docs/index.md',
    'https://milvus.io/docs/disk_index.md',
    'https://milvus.io/docs/scalar_index.md',
    'https://milvus.io/docs/performance_faq.md',
    'https://milvus.io/docs/product_faq.md',
    'https://milvus.io/docs/operational_faq.md',
    'https://milvus.io/docs/troubleshooting.md',
])

docs = loader.load()

# Split the documents into smaller chunks
text_splitter = RecursiveCharacterTextSplitter(chunk_size=1024, chunk_overlap=0)
all_splits = text_splitter.split_documents(docs)

After preparing the documents, the next step is to convert them into vector embeddings and save them in the vector store.

embeddings = OpenAIEmbeddings()
connection_args = { 'uri': URI, 'token': TOKEN }

vector_store = Milvus(
    embedding_function=embeddings,
    connection_args=connection_args,
    collection_name=COLLECTION_NAME,
    drop_old=True,
).from_documents(
    all_splits,
    embedding=embeddings,
    collection_name=COLLECTION_NAME,
    connection_args=connection_args,
)

To perform text-to-text similarity searches, use the following code snippet. The results will return the most relevant text in the document to the queries.

query = "What are the main components of Milvus?"
docs = vector_store.similarity_search(query)

print(len(docs))

The output should be similar to the following:

4

Ask your question

After preparing the documents, you can set up a chain to include them in a prompt. This will allow LLM to use the docs as a reference when preparing answers.

The following code snippet sets up a RAG chain using OpenAI as the LLM and a RAG prompt.

llm = ChatOpenAI(model_name="gpt-3.5-turbo", temperature=0) 
retriever = vector_store.as_retriever()

template = """Use the following pieces of context to answer the question at the end. 
If you don't know the answer, just say that you don't know, don't try to make up an answer. 
Use three sentences maximum and keep the answer as concise as possible. 
Always say "thanks for asking!" at the end of the answer. 
{context}
Question: {question}
Helpful Answer:"""
rag_prompt = PromptTemplate.from_template(template)

rag_chain = (
    {"context": retriever, "question": RunnablePassthrough()}
    | rag_prompt
    | llm
)

print(rag_chain.invoke("Explain IVF_FLAT in Milvus."))

The returned results include a content argument as the output_text.

# Output
#
# content='IVF_FLAT is an index mechanism in Milvus that divides a vector space into clusters. It compares the distances between a target vector and the centers of all clusters to find the nearest clusters. Then, it compares the distances between the target vector and the vectors in the selected clusters to find the nearest vectors. IVF_FLAT demonstrates performance advantages when the number of vectors exceeds the value of nlist. Thanks for asking!'

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