RAG Is A Hack - with Jerry Liu from LlamaIndex

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This post had robust discussion on HN and Twitter.

In October 2022, Robust Intelligence hosted an internal hackathon to play around with LLMs which led to the creation of two of the most important AI Engineering tools: LangChain 🦜⛓️ (our interview with Harrison here) and LlamaIndex 🦙 by Jerry Liu, which we’ll cover today. In less than a year, LlamaIndex has crossed 600,000 monthly downloads, raised $8.5M from Greylock, has a fast growing open source community that contributes to LlamaHub, and it doesn’t seem to be slowing down.

LlamaIndex’s Origin (aka GPT Tree Index)

Jerry struggled to make large amounts of data work with GPT-3 (which had a 4,096 tokens context window). Today LlamaIndex is at the forefront of the RAG wave (Retrieval Augmented Generation), but in the beginning Jerry wasn’t focused on embeddings and search, but rather on understanding how models could summarize, link, and reason about data.

On November 5th, Jerry pushed the first version to Github under the name “GPT Tree Index”:

The GPT Tree Index first takes in a large dataset of unprocessed text data as input. It then builds up a tree-index in a bottom-up fashion; each parent node is able to summarize the children nodes using a general summarization prompt; each intermediate node containing summary text summarizing the components below. Once the index is built, it can be saved to disk and loaded for future use.

Then, say the user wants to use GPT-3 to answer a question. Using a query prompt template, GPT-3 will be able to recursively perform tree traversal in a top-down fashion in order to answer a question. For example, in the very beginning GPT-3 is tasked with selecting between *n* top-level nodes which best answers a provided query, by outputting a number as a multiple-choice problem. The GPT Tree Index then uses the number to select the corresponding node, and the process repeats recursively among the children nodes until a leaf node is reached.

[…]

How is this better than an embeddings-based approach / other state-of-the-art QA and retrieval methods?

The intent is not to compete against existing methods. A simpler embedding-based technique could be to just encode each chunk as an embedding and do a simple question-document embedding look-up to retrieve the result. This project is a simple exercise to test how GPT can organize and lookup information.

The project attracted a lot of attention early on (the announcement tweet has ~330 likes), but it wasn’t until ~February 2023 that the open source community really started to explode, which was around the same time that LlamaHub was released. LlamaHub made it easy for developers to import data from Google Drive, Discord, Slack, databases, and more into their LlamaIndex projects.

What is LlamaIndex?

As we mentioned, LlamaIndex is leading the charge in the development of the RAG stack. RAG boils down to two parts:

* Indexing (i.e. how do you load and index the data in your knowledge base)

* Querying (i.e. how do you surface the data and fit it in the model context)

Indexing

To get your data from all your sources to your RAG knowledge base, you can leverage a few tools:

* Documents / Nodes: A Document is a generic container around any data source - for instance, a PDF, an API output, or retrieved data from a database. A Node is the atomic unit of data in LlamaIndex and represents a “chunk” of a source Document (i.e. one Document has many Node) as well as its relationship to other Node objects.

* Data Connectors: A data connector ingest data from different sources and turn them into Document representations (text and simple metadata). These connectors are offered through LlamaHub, and there are over 200 of them today.

* Data Indexes: Once you’ve ingested your data, LlamaIndex will help you index the data into a format that’s easy to retrieve. There are many types of indexes (Summary, Tree, Vector, etc). Under the hood, LlamaIndex parses the raw documents into intermediate representations, calculates vector embeddings, and infers metadata. The most commonly used index is the VectorStoreIndex, which can then be paired with any of the vector stores out there (an example with Chroma).

Querying

The RAG pipeline, during the querying phase, sources the most pertinent context from a user's prompt, forwarding it along to the LLM. This equips the LLM with current / private knowledge beyond its foundational training data. LlamaIndex offers adaptable modules tailored for building RAG pathways for Q&A, chatbots, or agent use, since each of them has different requirements. For example, a chatbot should expect the user to interject with follow up questions, while an agent will try to carry out a whole task on its own without user intervention.

Building Blocks

* Retrievers: A retriever defines how to efficiently retrieve relevant context from a knowledge base (i.e. index) when given a query. Vector index is the most popular mode, but there are other options like Summary, Tree, Keyword Table, Knowledge Graph, and Document Summary.

* Node Postprocessors: Once the retriever gets you Node objects back, you will need to do additional work like discarding low similarity ones. There are many options here as well, such as `SimilarityPostprocessor` (i.e. drop nodes below a certa