GUN

View Current Viewing Revision #10 from 12/13/2018 2:18 p.m.

Gun is an open-source and realtime, decentralized, offline-first, graph database engine written in JavaScript.

It is designed to be small and simple for fast data synchronization which runs everywhere JavaScript is supported. Gun is a fully distributed database aiming at scaling web application and correctly synchronizing data among devices with offline-first feature.

History

Gun was built by Mark Nadal in 2014.

He spent 4 years researching scaling up his web application, and eventually he found out it was hard with traditional databases or Master-Slave databases because of one big bottleneck, and decided to create the P2P database which can run on any browsers.

Isolation Levels

Snapshot Isolation

Gun allows offline usage and synchronizes data when online with eventual consistency. Each user has their own copy of data when using. Conflicts are handled by Hypothetical Amnesia Machine (HAM) when presented during synchronization.

Checkpoints

Not Supported

Gun does not support for checkpoints by default. But users may use third party adapters as the persistent layer like Amazon S3 to achieve checkpointing.

Concurrency Control

Optimistic Concurrency Control (OCC)

Gun is a offline-first database engine and uses eventual consistency. It allows users to view and update data when it is offline, and data will be synchronized when it is online. Gun uses a self-designed conflict resolution algorithm, Hypothetical Amnesia Machine (HAM), which combines timestamps and vector clocks to resolve conflicts and order data.

Storage Model

Custom

Gun stores records in JSON files. Data and relations are represented as a graph. Records are connected by references, called “souls” internally in Gun. Some official and simple queries similar in SQL are implemented with paths traversing. Complex operations among relations can be easily extended on graph.

Storage Architecture

Hybrid

Gun supports both the disk-oriented and in-memory mode. It is offline-first database where browser asks peers for data to use in memory and browser local storage the most often as cache. By default, Gun has a built-in persistent storage layer called Radix and there are some other available third-party persistent service options suggested by Gun.

Amazon S3
Level
MongoDB
Cassandra

System Architecture

Shared-Disk

In Gun, every node utilizes its own memory space and shares the persistent storage with the other peers. Gun implements its own transport layer protocol for P2P networking, Daisy-chain Ad-hoc Mesh-network (DAM). The ad hoc mesh network is used to coordinate with peers by messaging without producing too many duplicate rebroadcasting messages.

Compression

Prefix Compression

Gun uses radix tree to store user data in memory, and the Radisk is what the project team have designed for it to persist storage in Radix Tree by default. Gun also supports self-implemented or third-party persistent storage like Amazon S3, so data compression can be done outside of Gun.

Stored Procedures

Not Supported

Gun is a NoSQL database without stored procedures support.

Indexes

Patricia/Radix Trie

By default, Gun uses the Radisk Storage Engine as an in-memory and on-disk radix tree to store user data. Gun supports some existing persistent storage services like Amazon S3 to be plugged in, and also offers interfaces for developers to build persistent layer for it, so indexing can be flexible.