The Art of the Fugue: Minimizing Interleaving in Collaborative Text Editing

TL;DR

This paper introduces a new correctness property called maximal non-interleaving for replicated lists in collaborative text editing, and proposes two CRDT algorithms, Fugue and FugueMax, with FugueMax satisfying this property.

Contribution

The paper defines maximal non-interleaving, a novel correctness criterion, and develops two CRDT algorithms, with FugueMax proven to satisfy this property, improving consistency in collaborative editing.

Findings

Fugue offers performance comparable to existing CRDTs.

FugueMax guarantees maximal non-interleaving.

The problem of interleaving has been overlooked for decades.

Abstract

Most existing algorithms for replicated lists, which are widely used in collaborative text editors, suffer from a problem: when two users concurrently insert text at the same position in the document, the merged outcome may interleave the inserted text passages, resulting in corrupted and potentially unreadable text. The problem has gone unnoticed for decades, and it affects both CRDTs and Operational Transformation. This paper defines maximal non-interleaving, our new correctness property for replicated lists. We introduce two related CRDT algorithms, Fugue and FugueMax, and prove that FugueMax satisfies maximal non-interleaving. We also implement our algorithms and demonstrate that Fugue offers performance comparable to state-of-the-art CRDT libraries for text editing.