Conflict Free Replicated Data Types

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Collaboration with
Con
fl
ict Free Replicated Datatypes
(CRDTs)

What are CRDTs?

What are CRDTs?
Datatypes
Arrays
Maps
Text
Counters
Registers
...

Shared Datatypes?
CRDTs
Computer A
CRDTs
Computer B
Changes

Shared Datatypes?
CRDTs
Computer A
CRDTs
Computer B
Changes

Shared Datatypes?
Project X Document
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...

Shared Datatypes?
Project X Document
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consectetuer adipiscing elit.
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...

Shared Datatypes?
Project X Document
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consectetuer adipiscing elit.
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...

Shared Datatypes?
Project X Document
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consectetuer adipiscing elit.
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...

Project X Document
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dolor elementum
Do...

More than just
collaborative text editing...
About that example

It's about collaboration
in general
About that example

Working together
on a shared task
Collaboration?

Project X Document
Lorem ipsum dolor sit amet,
consectetuer adipiscing elit.
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dolor elementum
Do...

Project X Document
Lorem ipsum dolor sit amet,
consectetuer adipiscing elit.
Aenean commodo ligula eget
dolor elementum
Do...

Collaboration
Humans

Collaboration
Actors

What is collaborative software?

"collaborative software"
What examples come to mind?

Most software isn't
really collaborative

Most software isn't really collaborative
Why?

Why?
It's not easy

Project X Document
Lorem ipsum dolor sit amet,
consectetuer adipiscing elit.
Aenean commodo ligula eget
dolor elementum
Do...

We need better tools...
And that's what
CRDTs offer

CRDTs
How do you
use them?

How do they work?
De
fi
ne the shape
of your data
model

De
fi
ne the shape of your model...
CRDTs
Arrays
Maps
Sets
Registers
Counters
...
Arrays
Maps
Sets
Registers
Application
d...

How is data replicated
CRDTs
Application
data model
Application
data model
CRDTs

How is data replicated
CRDTs
Application
data model
Application
data model
CRDTs
Server

How is data replicated
CRDTs
Application
data model
Application
data model
CRDTs

No server required!
CRDTs

CRDTs
How do they
work?

CRDTs
Created following rules...
info to
merge changes
w/o con
fl
ict

To fully understand CRDTs...
Order theory
join semi-lattices

You probably don't need to know...
Order theory
unless you're a
CRDT library author

Still curious...
How CRDTs work?

First look at CRDTs
CRDT Counter

Counting things on a conveyor...
≤
Count: 2
1
0

Counting people entering a concert...

Counting people entering a concert...
Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
1 1 1
2 2 2
3 3 3

≤
Count: 2 Total Count
+ -
3 Total Count
+ -
3

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
1 1 1
Can we use primitives?
// model
count = ;
// model
count = 0;
...

Total Count
+ -
Total Count
+ -
Total Count
+ -
1 1 1
2 2 2
3 3 3
Can we use primitives?
// model
count = ;
// model
count...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
Can we use primitives?
// model
count = 0;
// model
count = 0;
// mo...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
Can we use primitives?
// model
count = 0;
// model
count = 0;
// mo...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
CRDT Counter
// model
counter =
new CRDTCounter();
// model
counter ...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
// model
counter =
new CRDTCounter();
// increment
counter.increment...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
// model
id = 100;
count = {}
// model
id = 200;
count = {}
// model...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
// model
id = 100;
count = {}
// model
id = 200;
count = {}
// model...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
// model
id = 100;
count = {}
// model
id = 200;
count = {}
// model...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0 0
// model
id = 100;
count = {
:
}
// model
id = 200;
count = {}
// mo...

Total Count
+ -
Total Count
+ -
Total Count
+ -
0 0
// model
id = 100;
count = {
:
}
// model
id = 200;
count = {
}
// mod...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
:
}
// model
id = 200;
count = {
}
// model
i...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
:
}
// model
id = 200;
count = {
}
// model
i...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
:
}
// model
id = 200;
count =
// model
id = ...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
: ,
}
// model
id = 200;
count =
// model
id ...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
: ,
}
// model
id = 200;
count =
// model
id ...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
: ,
,
}
// model
id = 200;
count =
// model
i...

Total Count
+ -
Total Count
+ -
Total Count
+ -
// model
id = 100;
count = {
: ,
,
}
// model
id = 200;
count =
// model
i...

CRDT Tradeoffs
Extra Memory / Metadata
Strong Eventual Consistancy

Networking Protocols
Websockets
WebRTC
...

Local First
No spinners
Multi device
Network optional
Data ownership

Libraries to look at
Yjs (JavaScript)
Automerge (JavaScript)
Y-crdt (Rust)
diamond-types (Rust)

Q & A

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