Leann revolutionizes Retrieval-Augmented Generation (RAG) by eliminating the storage bottleneck of traditional vector databases. Instead of pre-computing and storing billions of embeddings, Leann dynamically computes embeddings at query time using optimized graph-based search algorithms.

🎯 Why Leann?

Traditional RAG systems face a fundamental trade-off:

💾 Storage: Storing embeddings for millions of documents requires massive disk space
🔄 Memory overhead: The indexes LlamaIndex uses usually face high memory overhead (e.g., in-memory vector databases)
💰 Cost: Vector databases are expensive to scale

Leann revolutionizes this with Graph-based recomputation and cutting-edge system optimizations:

✅ Zero embedding storage - Only graph structure is persisted, reducing storage by 94-97%
✅ Real-time computation - Embeddings computed on-demand with low latency
✅ Memory efficient - Runs on consumer hardware with theoretical zero memory overhead
✅ Graph-based optimization - Advanced pruning techniques for efficient search while keeping low storage cost, with batching and overlapping strategies using low-precision search to optimize latency
✅ Pluggable backends - Support for DiskANN, HNSW, and other ANN algorithms (welcome contributions!)

🚀 Quick Start

Installation

git clone git@github.com:yichuan520030910320/LEANN-RAG.git leann
cd leann
git submodule update --init --recursive

macOS:

brew install llvm libomp boost protobuf
export CC=$(brew --prefix llvm)/bin/clang
export CXX=$(brew --prefix llvm)/bin/clang++
uv sync

Linux (Ubuntu/Debian):

sudo apt-get install libomp-dev libboost-all-dev protobuf-compiler libabsl-dev libmkl-full-dev libaio-dev
uv sync

30-Second Example

from leann.api import LeannBuilder, LeannSearcher

# 1. Build index (no embeddings stored!)
builder = LeannBuilder(backend_name="diskann")
builder.add_text("Python is a powerful programming language")
builder.add_text("Machine learning transforms industries")  
builder.add_text("Neural networks process complex data")
builder.build_index("knowledge.leann")

# 2. Search with real-time embeddings
searcher = LeannSearcher("knowledge.leann")
results = searcher.search("programming languages", top_k=2)

for result in results:
    print(f"Score: {result['score']:.3f} - {result['text']}")

Run the Demo

uv run examples/document_search.py

or you want to use python

source .venv/bin/activate
python ./examples/main_cli_example.py

PDF RAG Demo (using LlamaIndex for document parsing and Leann for indexing/search)

This demo showcases how to build a RAG system for PDF documents using Leann.

Place your PDF files (and other supported formats like .docx, .pptx, .xlsx) into the examples/data/ directory.
Ensure you have an OPENAI_API_KEY set in your environment variables or in a .env file for the LLM to function.

uv run examples/main_cli_example.py

✨ Features

🔥 Core Features

🔄 Real-time Embeddings - Eliminate heavy embedding storage with dynamic computation using optimized ZMQ servers and highly optimized search paradigm (overlapping and batching) with highly optimized embedding engine
📈 Scalable Architecture - Handles millions of documents on consumer hardware; the larger your dataset, the more LEANN can save
🎯 Graph Pruning - Advanced techniques to minimize the storage overhead of vector search to a limited footprint
🏗️ Pluggable Backends - DiskANN, HNSW/FAISS with unified API

🛠️ Technical Highlights

🔄 Recompute Mode - Highest accuracy scenarios while eliminating vector storage overhead
⚡ Zero-copy Operations - Minimize IPC overhead by transferring distances instead of embeddings
🚀 High-throughput Embedding Pipeline - Optimized batched processing for maximum efficiency
🎯 Two-level Search - Novel coarse-to-fine search overlap for accelerated query processing (optional)
💾 Memory-mapped Indices - Fast startup with raw text mapping to reduce memory overhead
🚀 MLX Support - Ultra-fast recompute with quantized embedding models, accelerating building and search by 10-100x (minimal example)

🎨 Developer Experience

Simple Python API - Get started in minutes
Extensible backend system - Easy to add new algorithms
Comprehensive examples - From basic usage to production deployment

Applications on your MacBook

📧 Lightweight RAG on your Apple Mail

LEANN can create a searchable index of your Apple Mail emails, allowing you to query your email history using natural language.

Quick Start

📋 Click to expand: Command Examples

# Use default mail path (works for most macOS setups)
python examples/mail_reader_leann.py

# Specify your own mail path
python examples/mail_reader_leann.py --mail-path "/Users/yourname/Library/Mail/V10/..."

# Run with custom index directory
python examples/mail_reader_leann.py --index-dir "./my_mail_index"

# Limit number of emails processed (useful for testing)
python examples/mail_reader_leann.py --max-emails 1000

# Run a single query
python examples/mail_reader_leann.py --query "Find emails about project deadlines"

Finding Your Mail Path

🔍 Click to expand: How to find your mail path

The default mail path is configured for a typical macOS setup. If you need to find your specific mail path:

Open Terminal
Run: find ~/Library/Mail -name "Messages" -type d | head -5
Use the parent directory(ended with Data) of the Messages folder as your --mail-path

Example Queries

💬 Click to expand: Example queries you can try

Once the index is built, you can ask questions like:

"Show me emails about meeting schedules"
"Find emails from my boss about deadlines"
"What did John say about the project timeline?"
"Show me emails about travel expenses"

🌐 Lightweight RAG on your Google Chrome History

LEANN can create a searchable index of your Chrome browser history, allowing you to query your browsing history using natural language.

Quick Start

📋 Click to expand: Command Examples

# Use default Chrome profile (auto-finds all profiles) and recommand method to run this because usually default file is enough
python examples/google_history_reader_leann.py


# Run with custom index directory
python examples/google_history_reader_leann.py --index-dir "./my_chrome_index"

# Limit number of history entries processed (useful for testing)
python examples/google_history_reader_leann.py --max-entries 500

# Run a single query
python examples/google_history_reader_leann.py --query "What websites did I visit about machine learning?"

# Use only a specific profile (disable auto-find)
python examples/google_history_reader_leann.py --chrome-profile "~/Library/Application Support/Google/Chrome/Default" --no-auto-find-profiles

Finding Your Chrome Profile

🔍 Click to expand: How to find your Chrome profile

The default Chrome profile path is configured for a typical macOS setup. If you need to find your specific Chrome profile:

Open Terminal
Run: ls ~/Library/Application\ Support/Google/Chrome/
Look for folders like "Default", "Profile 1", "Profile 2", etc.
Use the full path as your --chrome-profile argument

Common Chrome profile locations:

macOS: ~/Library/Application Support/Google/Chrome/Default
Linux: ~/.config/google-chrome/Default

Example Queries

💬 Click to expand: Example queries you can try

Once the index is built, you can ask questions like:

"What websites did I visit about machine learning?"
"Find my search history about programming"
"What YouTube videos did I watch recently?"
"Show me websites I visited about travel planning"

💬 Lightweight RAG on your WeChat History

LEANN can create a searchable index of your WeChat chat history, allowing you to query your conversations using natural language.

Prerequisites

🔧 Click to expand: Installation Requirements

First, you need to install the WeChat exporter:

sudo packages/wechat-exporter/wechattweak-cli install

Troubleshooting: If you encounter installation issues, check the WeChatTweak-CLI issues page.

Quick Start

📋 Click to expand: Command Examples

# Use default settings (recommended for first run)
python examples/wechat_history_reader_leann.py

# Run with custom export directory and wehn we run the first time, LEANN will export all chat history automatically for you
python examples/wechat_history_reader_leann.py --export-dir "./my_wechat_exports"

# Run with custom index directory
python examples/wechat_history_reader_leann.py --index-dir "./my_wechat_index"

# Limit number of chat entries processed (useful for testing)
python examples/wechat_history_reader_leann.py --max-entries 1000

# Run a single query
python examples/wechat_history_reader_leann.py --query "Show me conversations about travel plans"

Example Queries

💬 Click to expand: Example queries you can try

Once the index is built, you can ask questions like:

"我想买魔术师约翰逊的球衣，给我一些对应聊天记录?" (Chinese: Show me chat records about buying Magic Johnson's jersey)

⚡ Performance Comparison

LEANN vs Faiss HNSW

We benchmarked LEANN against the popular Faiss HNSW implementation to demonstrate the significant memory and storage savings our approach provides:

# Run the comparison benchmark
python examples/compare_faiss_vs_leann.py

🎯 Results Summary

Metric	Faiss HNSW	LEANN HNSW	Improvement
Peak Memory	887.0 MB	618.2 MB	1.4x less (268.8 MB saved)
Storage Size	5.5 MB	0.5 MB	11.4x smaller (5.0 MB saved)

📈 Key Takeaways

🧠 Memory Efficiency: LEANN uses 30% less memory during index building and querying
💾 Storage Optimization: LEANN requires 91% less storage for the same dataset
🔄 On-demand Computing: Storage savings come from computing embeddings at query time instead of pre-storing them
⚖️ Fair Comparison: Both systems tested on identical hardware with the same 2,573 document dataset

Note

: Results may vary based on dataset size, hardware configuration, and query patterns. The comparison excludes text storage to focus purely on index structures.

Run the comparison

python examples/compare_faiss_vs_leann.py

Benchmark results obtained on Apple Silicon with consistent environmental conditions

📊 Benchmarks

How to Reproduce Evaluation Results

Reproducing our benchmarks is straightforward. The evaluation script is designed to be self-contained, automatically downloading all necessary data on its first run.

1. Environment Setup

First, ensure you have followed the installation instructions in the Quick Start section. This will install all core dependencies.

Next, install the optional development dependencies, which include the huggingface-hub library required for automatic data download:

# This command installs all development dependencies
uv pip install -e ".[dev]"

2. Run the Evaluation

Simply run the evaluation script. The first time you run it, it will detect that the data is missing, download it from Hugging Face Hub, and then proceed with the evaluation.

To evaluate the DPR dataset:

python examples/run_evaluation.py data/indices/dpr/dpr_diskann

To evaluate the RPJ-Wiki dataset:

python examples/run_evaluation.py data/indices/rpj_wiki/rpj_wiki.index

The script will print the recall and search time for each query, followed by the average results.

Storge Usage Comparison

System	DPR(2M docs)	RPJ-wiki(60M docs)	Chat history()
Traditional Vector DB(LLamaindex faiss)	x GB	x GB	x GB
Leann	xx MB	x GB	x GB
Reduction	x%	x%	x%

Memory Usage Comparison

System	DPR(2M docs)	RPJ-wiki(60M docs)	Chat history()
Traditional Vector DB(LLamaindex faiss)	x GB	x GB	x GB
Leann	xx MB	x GB	x GB
Reduction	x%	x%	x%

Query Performance of LEANN

Backend	Index Size	Query Time	Recall@3
DiskANN	1M docs	xms	0.95
HNSW	1M docs	xms	0.95

Benchmarks run on Apple M3 Pro 36 GB

🏗️ Architecture

Key Components

🧠 Embedding Engine: Real-time transformer inference with caching
📊 Graph Index: Memory-efficient navigation structures
🔄 Search Coordinator: Orchestrates embedding + graph search
⚡ Backend Adapters: Pluggable algorithm implementations

🔬 Paper

If you find Leann useful, please cite:

LEANN: A Low-Storage Vector Index

@misc{wang2025leannlowstoragevectorindex,
      title={LEANN: A Low-Storage Vector Index}, 
      author={Yichuan Wang and Shu Liu and Zhifei Li and Yongji Wu and Ziming Mao and Yilong Zhao and Xiao Yan and Zhiying Xu and Yang Zhou and Ion Stoica and Sewon Min and Matei Zaharia and Joseph E. Gonzalez},
      year={2025},
      eprint={2506.08276},
      archivePrefix={arXiv},
      primaryClass={cs.DB},
      url={https://arxiv.org/abs/2506.08276}, 
}

🤝 Contributing

We welcome contributions! Leann is built by the community, for the community.

Ways to Contribute

🐛 Bug Reports: Found an issue? Let us know!
💡 Feature Requests: Have an idea? We'd love to hear it!
🔧 Code Contributions: PRs welcome for all skill levels
📖 Documentation: Help make Leann more accessible
🧪 Benchmarks: Share your performance results

Development Setup

git clone git@github.com:yichuan520030910320/LEANN-RAG.git leann
cd leann
git submodule update --init --recursive
uv sync --dev
uv run pytest tests/

Quick Tests

# Sanity check all distance functions
uv run python tests/sanity_checks/test_distance_functions.py

# Verify L2 implementation
uv run python tests/sanity_checks/test_l2_verification.py

❓ FAQ

Common Issues

NCCL Topology Error

Problem: You encounter ncclTopoComputePaths error during document processing:

ncclTopoComputePaths (system=<optimized out>, comm=comm@entry=0x5555a82fa3c0) at graph/paths.cc:688

Solution: Set these environment variables before running your script:

export NCCL_TOPO_DUMP_FILE=/tmp/nccl_topo.xml
export NCCL_DEBUG=INFO
export NCCL_DEBUG_SUBSYS=INIT,GRAPH
export NCCL_IB_DISABLE=1
export NCCL_NET_PLUGIN=none
export NCCL_SOCKET_IFNAME=ens5

📈 Roadmap

🎯 Q2 2025

DiskANN backend with MIPS/L2/Cosine support
HNSW backend integration
Real-time embedding pipeline
Memory-efficient graph pruning

🚀 Q3 2025

Advanced caching strategies
GPU-accelerated embedding computation
Add sleep-time-compute and summarize agent! to summarilze the file on computer!
Add OpenAI recompute API

🌟 Q4 2025

Integration with LangChain/LlamaIndex
Visual similarity search
Query rewrtiting, rerank and expansion

📄 License

MIT License - see LICENSE for details.

🙏 Acknowledgments

Microsoft Research for the DiskANN algorithm
Meta AI for FAISS and optimization insights
HuggingFace for the transformer ecosystem
Our amazing contributors who make this possible

⭐ Star us on GitHub if Leann is useful for your research or applications!

Made with ❤️ by the Leann team

Description

RAG on Everything with LEANN. Enjoy 97% storage savings while running a fast, accurate, and 100% private RAG application on your personal device.

ai faiss gpt-oss langchain llama-index llm localstorage offline-first ollama privacy python rag retrieval-augmented-generation vector-database vectors vector-search

Readme MIT 80 MiB