Kevin Jahns

docs.yjs.dev

Overview, scope, challenges

Modern Collaborative Applications

Desirable Properties:

Synchronize automatically
Application is available offline
Visualization of change history

Tracking changes example:

The Yjs Framework

Yjs for collaborative application state

Uses CRDTs to synchronize changes.
- Based on the YATA CRDT
Associate tracked changes with users
Offline & Network Agnostic

github.com/yjs/yjs

CRDTs in the real-world

Challenges

Tracking the editing history incurs overhead

Observation

While the amount of content that a user can insert is virtually unbounded, the amount of operations a user can call is not.
- I.e. A user typing at 30 characters per second non-stop for 1 year can only produce ~16 millions keystrokes
- We can optimize for user-behavior

The Yjs Algorithm

Compound representation of insertions
..
..

Compressing Changes

client="Bob"

clock=0

client="Bob"

clock=1

client="Bob"

clock=2

ABC

client="Bob"

clock=0

The Yjs Algorithm

Compound representation of insertions
Simple pruning scheme for untracked deleted content
..

Compressing Changes

client="Bob"

clock=0

client="Bob"

clock=1

client="Bob"

clock=2

ABC

client="Bob"

clock=0

len = 3

deleted=true

client="Bob"

clock=0

The Yjs Algorithm

Compound representation of insertions
Simple pruning scheme for untracked deleted content
Binary compression for encoding document updates (variable length encoding, run-length encoding, custom JSON encoder)

Compressing Changes

More details: Kevin's Blog

client="Bob"

clock=0

client="Bob"

clock=1

client="Bob"

clock=2

ABC

client="Bob"

clock=0

len = 3

deleted=true

client="Bob"

clock=0

Benchmarking

[B4] Real-world editing trace

Research paper (17 pages)
182,315 single-character insertion operations
77,463 single-character deletion operations
259,778 operations totally

Results

	Yjs	Automerge	Automerge (performance branch)	delta-crdts
Time to apply changes	6 s	490 s	750s	20134 s
Encoded document	0.160 MB	84 MB	0.296 MB	7.9 MB
Memory usage	3.2MB	1.1 GB	~	34.4 MB
Loading to memory	0.086 s	38 s	208 s	52 s

github.com/dmonad/crdt-benchmarks

Benchmarking

[B4x100] Real-world editing trace

Apply the [B4] 100 times.
25,977,800 operations totally
10 million characters in the final document
For comparison: The novel "Game of Thrones: A song of Ice and Fire" only contains 1.6 million characters

Results