CRDT Conflict-Free Replicated Data Types

https://www.youtube.com/watch?v=FG5Varj1Ows&list=PLjTveVh7FakLdTmm42TMxbN8PvVn5g4KJ&index=21&ab_channel=Jordanhasnolife https://velog.io/@heelieben/%EC%8B%A4%EC%8B%9C%EA%B0%84-%EB%8F%99%EC%8B%9C-%ED%8E%B8%EC%A7%91-OT-%EC%99%80-CRDT

1. Last Write wins(LWW)
2. detect concurrent writes and sotre siblings
3. Have db merge them

what is a CRDT

• 어떤 변경사항을 받을때, 순서와 관계없이 변경사항만 같으면 같은 상태
• 각 문자에 고유한 id를 부여하고 이를 기반으로 보정함

Where are CRDTs used?

• Riak
• Redis (sets in Redis enterprise)

downsides

• add ham, remove ham 에서 add ham 이 replication 과정에서 실패하면 어떻게 할 것임?
• we need casually consistent message delivery no drops, no duplicate
• idempotent: same thing many times and no different

state-based CRDTs merge function must be

• commutative
• Associative
• Idempotent

gossip protocol

• no extra messaging infra
• 2