300 lines
15 KiB
Markdown
300 lines
15 KiB
Markdown
# RAG
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Retrieval Augmented Generation (RAG) is a method of minimizing LLM hallucinations and extending the model's context
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without consuming a significant portion of the context length. It uses documents and other additional resources that you
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provide to give the model more context for all of your prompts.
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Loki has a built-in vector database and full-text search engine to support RAG knowledge bases for your queries.
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The generated knowledge bases are stored in the `rag` subdirectory of your Loki configuration directory. The location of
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this directory varies by system, so you can use the following command to find your RAG directory:
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```shell
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loki --info | grep 'rags_dir' | awk '{print $2}'
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```
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## Quick Links
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<!--toc:start-->
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- [Usage](#usage)
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- [Persistent RAG](#persistent-rag)
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- [Ephemeral RAG](#ephemeral-rag)
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- [How It Works](#how-it-works)
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- [1. Build](#1-build)
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- [2. Lookup](#2-lookup)
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- [2a. Reranking (Optional)](#2a-reranking-optional)
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- [3. Prompt](#3-prompt)
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- [Supported Document Sources](#supported-document-sources)
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- [Document Loaders](#document-loaders)
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- [Document Loader Usage](#document-loader-usage)
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- [Advanced Customizations](#advanced-customizations)
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- [Embedding Model](#embedding-model)
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- [Reranker](#reranker)
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- [Chunk Size](#chunk-size)
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- [Trade-Offs](#chunk-size-trade-offs)
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- [Chunk Overlap](#chunk-overlap)
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- [Top K](#top-k)
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- [Trade-Offs](#top-k-trade-offs)
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- [RAG Template](#rag-template)
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<!--toc:end-->
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---
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## Usage
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There's two ways to use RAG in Loki: A persistent RAG that can be loaded on-demand for queries, and an ephemeral one for
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adding RAG to a single specific query.
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### Persistent RAG
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In the REPL, persistent RAG is initialized via the `.rag` command:
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The generated RAG is then saved to the `rag` subdirectory of the Loki configuration, and can then be loaded whenever you
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want that knowledge base via either `.rag <name>` or `loki --rag <RAG>`.
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### Ephemeral RAG
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Short-lived RAG that is only used for a single session or query is loaded using `.file`/`--file`.
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You can use it to either execute a prompt from a file, or for temporary RAG. The difference is the usage of the `--`
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separator. If you only specify a filename and no `--` separator, Loki will know to read the file contents and pass them
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as a query to the model. Otherwise, the `--` separator is read to indicate that this is the end of the list of documents
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to load into the ephemeral RAG, and what follows is the query to pass to the model.
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```shell
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.file prompt.md # Read the file as a prompt
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.file %% -- translate the last reply to italian
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.file `git diff` -- generate a commit message
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```
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Once the session ends, this RAG will no longer be accessible and is only visible to the current session.
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#### The `%%` Document Type
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In addition to the usual documents that can be specified for persistent RAG, ephemeral RAG has a special `%%` value.
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This value references the content of the last reply. So you can use it like this:
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```shell
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.file %% -- translate the last reply to italian
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```
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The `--` indicates that this is the end of your documents and the beginning of your prompt.
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#### The `cmd` Document Type
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Loki also lets you use command outputs for ephemeral RAG input. Simply enclose the command in backticks:
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```shell
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.file `git diff` -- generate a commit message
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```
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The `--` indicates that this is the end of your documents and the beginning of your prompt.
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## How It Works
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#### 1. Build
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When you define RAG, Loki will first "build" the RAG. This means that Loki will consume the documents you specified and
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generate [embeddings](https://huggingface.co/spaces/hesamation/primer-llm-embedding) for that text. This essentially just means that Loki translates the document into a language
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the LLM can understand.
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These embeddings are then stored in an in-memory vector database.
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#### 2. Lookup
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Loki sits between you and the model. So when you submit a prompt to the model, before Loki ever sends it, it will first
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convert your prompt into embeddings (LLM language), and look for relevant snippets of text in the vector database.
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Loki then passes the top `n`-snippets of text that it finds in the vector database as additional context to the model
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before your prompt.
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#### 2a. Reranking (Optional)
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The lookup for relevant snippets of texts uses embeddings to find text that is semantically similar to your prompt, and
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returns the top `n`-results. This often works fairly well, however these top results aren't always the most relevant for
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answering the specific query.
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Reranking improves these initial results (say, the top 20-100 text snippets) and re-scores them using a more
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sophisticated model. The reranker model will rank documents by their actual usefulness for answering the query to ensure
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the most relevant context is passed to the model alongside your query.
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This reranking model can be customized for each RAG you build in Loki. See the [Custom Reranker](#reranker) section
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below for more details on how to customize this.
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#### 3. Prompt
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Finally, the text snippets that were looked up in RAG are passed to the model as additional context to your prompt,
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giving the model query-specific context to answer your question.
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## Supported Document Sources
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Loki supports a number of document sources that can be used for RAG:
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| Source | Example | Comments |
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|--------------------------|-----------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------|
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| Files | `/tmp/dir1/file1;/tmp/dir1/file2` | |
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| Directory | `/tmp/dir` | Picks up all files in a directory and all its subdirectories |
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| Directory (extensions} | `/tmp/dir2/**/*.{md,txt}` | Finds all files in all subdirectories with the specified extensions |
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| Recursive Filename | `/tmp/*/LOKI.md` | The following files will be picked up: <br><ul><li>`/tmp/dir1/LOKI.md`</li><li>`/tmp/dir2/subdir1/LOKI.md`</li><li>`/tmp/dir2/subdir2/LOKI.md`</li></ul> |
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| URL | `https://www.ohdsi.org/data-standardization/` | Downloads and loads the specified webpage into the <br>knowledge base |
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| Recursive URL (Websites) | `https://github.com/OHDSI/Vocabulary-v5.0/wiki/**` | Crawls all pages under the given URL and loads them <br>into the knowledge base |
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| Document Loader (custom) | `jina:https://cloud.google.com/bigquery/docs/reference/standard-sql/` | Use a custom document loader to parse the given document |
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## Document Loaders
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Loki only has built-in support for loading text files. But that functionality can be extended to read all kinds of files
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into your knowledge bases. These custom loaders are used by both RAG and for documents specified using the
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`.file`/`--file` flags.
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In the global configuration file, you can specify loaders for specific document types using the `document_loaders`
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setting. Each loader is defined by specifying a name and then a command that Loki will execute to load the document.
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The following variables are interpolated at runtime by Loki and can be used as placeholders in your command definitions:
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* `$1` (Required) - The input file
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* `$2` (Optional) - The output file. If omitted, `stdout` is used as the output destination
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**Note:** It is your responsibility to ensure that any tools used to parse documents into text that Loki can read are
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installed on your system and are available on your `$PATH`. Loki does not have any built-in way of installing
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dependencies for document loaders for you.
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The following are some example loaders:
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```yaml
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document_loaders:
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pdf: 'pdftotext $1 -' # Use pdftotext to convert a PDF file to text
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# (see https://poppler.freedesktop.org for details on how to install pdftotext)
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docx: 'pandoc --to plain $1' # Use pandoc to convert a .docx file to text
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# (see https://pandoc.org for details on how to install pandoc)
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jina: 'curl -fsSL https://r.jina.ai/$1 -H "Authorization: Bearer {{JINA_API_KEY}}' # Use Jina to translate a website into text;
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# Requires a Jina API key to be added to the Loki vault
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git: > # Use yek to load a git repository into the knowledgebase (https://github.com/bodo-run/yek)
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sh -c "yek $1 --json | jq 'map({ path: .filename, contents: .content })'"
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```
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### Document Loader Usage
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Once you have your loaders defined, you can specify when Loki should use them by prefixing any RAG file/directory/URI
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with the name of the loader.
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**Example: Load a git repo into RAG**
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**Example: Use pdf loader for ephemeral RAG**
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```shell
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$ loki --file pdf:some-file.pdf
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```
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## Advanced Customizations
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For those familiar with RAG, Loki exposes a handful of advanced global settings that can be used to tweak your default
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RAG configurations.
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### Embedding Model
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When Loki queries your RAG knowledge bases, it needs to first convert your query into embeddings. By default, Loki uses
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the same embedding model that was used to create the knowledge base in the first place.
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This can be customized to any other embedding model available in your configured clients by setting the
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`rag_embedding_model` setting in your global Loki configuration file:
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```yaml
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rag_embedding_model: null # Specifies the embedding model used for context retrieval
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```
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### Reranker
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By default, Loki uses [Reciprocal Rank Fusion (RRF)](https://www.elastic.co/docs/reference/elasticsearch/rest-apis/reciprocal-rank-fusion) to merge vector and keyword search results.
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You can change the default reranker model to any other reranking model in your configured clients. To change the default
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reranker model, simply change the value of the `rag_reranker_model` setting in your global configuration file:
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```yaml
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rag_reranker_model: null # By default,
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```
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### Chunk Size
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In the context of RAG, the chunk size is the maximum length of each text chunk (measured in characters) that is created
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when splitting documents. In Loki, this defaults to `2000` characters.
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You can specify a different global default by setting the `rag_chunk_size` property in your global configuration file:
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```yaml
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rag_chunk_size: null # Defines the size of chunks for document processing in characters
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```
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#### Chunk Size Trade-Offs
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Keep in mind the following trade-offs when changing the chunk size:
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* **Smaller chunks (e.g. 256 characters):** More precise retrieval, better semantic focus, but may lack context or split
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important information
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* **Larger chunks (e.g. 1024 characters):** More context preserved, fewer chunks to manage, but less precise matching
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and more noise in retrieved document
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### Chunk Overlap
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Chunk overlap in RAG is the number of characters that overlap between consecutive chunks to maintain continuity.
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---
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**Example:** If the following sentence is cut off at the end of one chunk
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`I was doing fine until someone brought up`
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You'll ideally want that full sentence to be picked up at the beginning of the next chunk to make sure the full meaning
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is captured. So in this example, if your chunk overlap is 42 characters, then the start of the next chunk would look
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like this:
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`I was doing fine until someone brought up the game. <next sentence>`
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---
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Often, this value is 10%-20% of the chunk size.
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By default, in Loki, this value is 5% the chunk size. You can override this and specify the default chunk overlap (in
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characters) that Loki should use as a global default by setting the `rag_chunk_overlap` property in the global Loki
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configuration file:
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```yaml
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rag_chunk_overlap: null # Defines the overlap between chunks
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```
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### Top K
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In RAG, `top_k` represents the top `k`-chunks to return from the vector database query. Think of it like if you search
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something on Google and only care about the top 10 results, that's what you'll use for your context.
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In Loki, the default value for this is `5`. You can customize this global default by setting the `rag_top_k` property in
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your global configuration file:
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```yaml
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rag_top_k: 5 # Specifies the number of documents to retrieve for answering queries
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```
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#### Top K Trade-Offs
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When customizing this value, keep in mind the following trade-offs so you get the best performance:
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* **Lower top_k (e.g. 3):** Faster, more focused context, lower cost, but risks missing relevant information
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* **Higher top_k (e.g. 10):** More comprehensive coverage, but more noise, higher latency, increased token costs, and
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potential context window constraints
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### RAG Template
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When you use RAG in Loki, after Loki performs the lookup for relevant chunks of text to add as context to your query, it
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will add the retrieved text chunks as context to your query before sending it to the model. The format of this context
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is determined by the `rag_template` setting in your global Loki configuration file.
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This template utilizes two placeholders:
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* `__INPUT__`: The user's actual query
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* `__CONTEXT__`: The context retrieved from RAG
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These placeholders are replaced with the corresponding values into the template and make up what's actually passed to
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the model at query-time.
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The default template that Loki uses is the following:
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```text
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Answer the query based on the context while respecting the rules. (user query, some textual context and rules, all inside xml tags)
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<context>
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__CONTEXT__
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</context>
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<rules>
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- If you don't know, just say so.
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- If you are not sure, ask for clarification.
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- Answer in the same language as the user query.
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- If the context appears unreadable or of poor quality, tell the user then answer as best as you can.
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- If the answer is not in the context but you think you know the answer, explain that to the user then answer with your own knowledge.
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- Answer directly and without using xml tags.
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</rules>
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<user_query>
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__INPUT__
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</user_query>
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```
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You can customize this template by specifying the `rag_template` setting in your global Loki configuration file. Your
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template *must* include both the `__INPUT__` and `__CONTEXT__` placeholders in order for it to be valid.
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