Delete Operations in Yjs: A Different Approach to CRDTs

In the realm of collaborative editing and distributed systems, Conflict-free Replicated Data Types (CRDTs) play a crucial role in ensuring data consistency across multiple users. Yjs, a popular CRDT library, stands out with its distinctive approach to handling delete operations, deviating from the norm of treating them as inverse insertions.

Insertion vs. Deletion in Yjs

When an insertion occurs in Yjs, it is implemented as a sequence-based CRDT operation. Each insertion is assigned a unique timestamp, and when conflicts arise, the operation with the highest timestamp prevails. This approach allows for straightforward conflict resolution and guarantees eventual consistency.

However, deletion operations in Yjs follow a different paradigm. Instead of being treated as inverse insertions, they are handled as tombstones. A tombstone marks a deleted element as logically removed, but it does not physically delete it from the document. This approach has several advantages:

• Efficiency: Tombstones prevent the need to physically remove deleted elements, reducing network traffic and storage overhead.
• Reversibility: Tombstones allow for easy undo and redo operations, as deleted elements can be restored simply by removing the tombstone.
• Conflict Avoidance: Tombstones help avoid conflicts by ensuring that multiple users cannot simultaneously delete the same element.

Implications for Collaboration

Yjs's unique handling of delete operations has significant implications for collaborative editing and distributed systems:

• Undo and Redo: Users can easily undo or redo deletions, providing flexibility and reducing the risk of accidental data loss.
• Concurrency: Tombstones prevent conflicts when multiple users attempt to delete the same element, ensuring data integrity.
• Versioning: Tombstones allow for fine-grained version control, enabling users to track changes and restore previous versions of documents.

Conclusion

Yjs's approach to delete operations in CRDTs deviates from the traditional inverse insertion method, offering advantages in efficiency, reversibility, and conflict avoidance. This unique approach contributes to the effectiveness of Yjs as a CRDT library, facilitating seamless collaboration and data consistency in distributed systems.