piChain

piChain is a library which implements a fault-tolerant distributed state machine that inherits features of Paxos, providing strong consistency, and of a blockchain, providing eventual consistency and simplicity. For example the library can be used to keep replicas of a distributed data storage consistent in case of failures.

Requirements

Python 3.6, pip

Installation

It is recommended to install piChain inside a virtual environment.

Setup a virtual environment:

virtualenv --python=python3 <venv-name>
source <venv-name>/bin/activate

Install piChain:

git clone https://github.com/florianmorath/piChain.git
cd piChain
pip install -r requirements.txt
python setup.py install

Note: before running pip install -r requirements.txt you need to have a leveldb instance installed. The installation process depends on the OS. For macOS do the following:

brew install leveldb
CFLAGS='-mmacosx-version-min=10.7 -stdlib=libc++' pip install --no-use-wheel plyvel

Usage

First, one needs to setup the Node instances (each node represents a peer in the network):
A Node constructor takes two arguments, a node index and a peers dictionary. The peers dictionary contains an (ip,port) pair for each node. With the node_index argument one can select which node from the peers dictionary is running “locally”.
The tx_committed field of a Node instance is a callable that is called once a transaction has been committed. By calling start_server() on the Node instance the local node will try to connect to its peers.
Note: start_server() starts the twisted main loop.

from piChain import Node
def tx_committed(commands):
    """
    Args:
        commands (list of str): List of committed Transaction commands.
    """
    for command in commands:
        print('command committed: %s' % command)
def main():
    node_index = 0
    peers = {
        '0': {'ip': '127.0.0.1', 'port': 7982},
        '1': {'ip': '127.0.0.1', 'port': 7981},
        '2': {'ip': '127.0.0.1', 'port': 7980}
    }
    node = Node(node_index, peers)
    node.tx_committed = tx_committed
    node.start_server()

Transactions can be committed by calling make_txn('command') on a Node instance:

node.make_txn('command')

Performance

This plot shows the benchmark results of how many Requests Per Second (RPS) piChain can handle for different cluster sizes.

More information

There is a distributed database implementation in the examples folder to demonstrate an application of the piChain package.
The API documentation can be build as follows: (requires installation of the piChain package)
```
pip install sphinx
pip install sphinxcontrib-napoleon
cd docs
make html
```