lambdaclass/merkle_patricia_tree

Table of Contents

• Disclaimer
• About
• Usage
  • Testing
• Benchmarking
• Contributing
• Documentation
  • What is a patricia merke tree
  • Terms Used
  • Useful links
• License

⚠️ Disclaimer

🚧 This project is a work-in-progress and is not ready for production yet. Use at your own risk. 🚧

📖 About

This crate contains an implementation of a Patricia Tree.

Its structure is implemented to match Ethereum's Patricia Merkle Trees.

🚀 Usage

Here's an example to calculate the hash after inserting a few items.

use merkle_patricia_tree::PatriciaMerkleTree;
use sha3::Keccak256;

let mut tree = PatriciaMerkleTree::<&[u8], &[u8], Keccak256>::new();
tree.insert(b"doe", b"reindeer");
tree.insert(b"dog", b"puppy");
tree.insert(b"dogglesworth", b"cat");

let hash = tree.compute_hash().unwrap();
println!("{hash:02x}");

Testing

Run the following command:

make test

📊 Benchmarking

make bench

To run external benches:

Run the one-time setup

make ext-bench-prepare

make ext-bench

Benchmarks are provided for the following use cases:

• Retrieval of non-existant nodes.
• Retrieval of existing nodes.
• Insertion of new nodes.
• Overwriting nodes.
• Removal of nodes.
• Removal of non-existing nodes (no-op).
• Calculate the root Keccak256 hash.

Every use case is tested with different tree sizes, ranging from 1k to 1M.

On a AMD Ryzen 9 5950x 3.4 Ghz with 128 Gb RAM using Keccak256 as the hash function:

Gets	Inserts

Requires hyperfine:

make storage-bench

Profiling

Dependencies: valgrind, gnuplot, make

You can profile some example programs and generate plots using the following command:

make profile

Normal	From Sorted Iter

🛠 Contributing

The open source community is a fantastic place for learning, inspiration, and creation, and this is all thanks to contributions from people like you. Your contributions are greatly appreciated.

If you have any suggestions for how to improve the project, please feel free to fork the repo and create a pull request, or open an issue with the tag 'enhancement'.

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature/AmazingFeature)
3. Commit your Changes (git commit -m 'Add some AmazingFeature')
4. Push to the Branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

📚 Documentation

What is a Patricia Merkle Tree

PATRICIA is an acronym which means:

Practical Algorithm to Retrieve Information Coded in Alphanumeric

A compact representation of a trie in which any node that is an only child is merged with its parent.

Patricia tries are seen as radix trees with radix equals 2, which means that each bit of the key is compared individually and each node is a two-way (i.e., left versus right) branch

In essence, a patricia tree stores a value for the given path.

The path is encoded into bytes, and then each nibble of each byte is used to traverse the tree.

It is composed of 3 different types of nodes:

The branch node

It contains a 17 element array:

• The 16 first elements cover every representable value of a nibble (2^4 = 16)
• The value in case the path is fully traversed.

The leaf node

It contains 2 elements:

• The encoded path.
• The value.

The extension node

It contains 2 elements:

• The prefix as a segment of the path.
• A reference to the child node (which must be a branch).

This node allows the tree to be more compact, imagine we have a path that ultimately can only go 1 way, because it has no diverging paths, adding X nodes instead of 1 representing that would be a waste of space, this fixes that.

For example, imagine we have the paths "abcdx" and "abcdy", instead of adding 10 nodes (1 for each nibble in each character), we create a single node representing the path "abcd", thus compressing the tree.

Solving the ambiguity

Since traversing a path is done through it's nibbles, when doing so, the remaining partial path may have an odd number of nibbles left, this introduces an ambiguity that comes from storing a nibble as a byte:

Imagine we have the following remaining nibbles:

• 1
• 01

When representing both as a byte, they have the same value 1.

Thats why a flag is introduced to differenciate between an odd or even remaining partial path:

[flag] + path

Terms Used

• nibble: 4bits, half a byte, a single hex digit.

Useful links

• Patricia tree on NIST
• Paper by Donald R. Morrison

⚖️ License

This project is licensed under the Apache 2.0 license.

See LICENSE for more information.