A Conflict-Free Replicated JSON Datatype

TL;DR

This paper introduces a conflict-free replicated JSON data type (CRDT) that ensures consistent, convergent updates across distributed systems without data loss, supporting nested structures and client-side merging for unreliable networks.

Contribution

It presents a novel algorithm and formal semantics for a JSON CRDT capable of handling nested data and concurrent modifications without central coordination.

Findings

Supports arbitrarily nested lists and maps

Performs all merging client-side without network ordering

Ensures all replicas converge to the same state

Abstract

Many applications model their data in a general-purpose storage format such as JSON. This data structure is modified by the application as a result of user input. Such modifications are well understood if performed sequentially on a single copy of the data, but if the data is replicated and modified concurrently on multiple devices, it is unclear what the semantics should be. In this paper we present an algorithm and formal semantics for a JSON data structure that automatically resolves concurrent modifications such that no updates are lost, and such that all replicas converge towards the same state (a conflict-free replicated datatype or CRDT). It supports arbitrarily nested list and map types, which can be modified by insertion, deletion and assignment. The algorithm performs all merging client-side and does not depend on ordering guarantees from the network, making it suitable for deployment on mobile devices with poor network connectivity, in peer-to-peer networks, and in messaging systems with end-to-end encryption.