Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Speaker Deck
PRO
Sign in
Sign up for free
CRDTs - The science behind Phoenix Presence
Maciej Kaszubowski
May 25, 2017
Programming
2
160
CRDTs - The science behind Phoenix Presence
Maciej Kaszubowski
May 25, 2017
Tweet
Share
More Decks by Maciej Kaszubowski
See All by Maciej Kaszubowski
Error-free Elixir
mkaszubowski
0
110
Modular Design in Elixir (ElixirConf EU 2019)
mkaszubowski
2
430
The Big Ball of Nouns
mkaszubowski
0
78
Modular Design in Elixir
mkaszubowski
1
210
Our three years with Elixir
mkaszubowski
0
95
Concurrency Basics for Elixir
mkaszubowski
0
56
Distributed Elixir
mkaszubowski
0
55
Software Architecture
mkaszubowski
0
53
Let it crash - fault tolerance in Elixir/OTP
mkaszubowski
0
200
Other Decks in Programming
See All in Programming
NieR Re[in]carnationにおけるUnityアニメーション活用術
applibot
1
870
Android入門
hn410
0
310
SPA/MPA 議論の俯瞰と 現代における設計のポイント - #tfcon 2022 フロントエンド設計
ahomu
3
1.9k
Unboxing Rails 7
claudiob
1
120
The future of trust stores in Python
sethmlarson
0
190
The Success of Rails: Ensuring Growth for the Next 100 Years
eileencodes
3
550
WindowsコンテナDojo:第2回 Windowsコンテナアプリのビルド、公開、デプロイ
oniak3ibm
PRO
0
150
CLI構築のススメ
nyankotaro
1
250
既存画面の Jetpack Composeでの書き換え: FAANSでの事例紹介 / Case study of rewriting existing screens with Jetpack Compose
horie1024
0
330
Kotlin 最新動向2022 #tfcon #techfeed
ntaro
1
1.2k
クリエイティブ系のウェブサイト制作で役立つCSS技法 / CSS for develop creative website
clockmaker
2
1.7k
GraphQL+KMM開発でわかったこと / What we learned from GraphQL+KMM development
kubode
0
130
Featured
See All Featured
Rebuilding a faster, lazier Slack
samanthasiow
62
7.2k
Typedesign – Prime Four
hannesfritz
33
1.3k
Automating Front-end Workflow
addyosmani
1351
200k
Git: the NoSQL Database
bkeepers
PRO
415
59k
Gamification - CAS2011
davidbonilla
75
3.9k
The Most Common Mistakes in Cover Letters
jrick
PRO
4
24k
Java REST API Framework Comparison - PWX 2021
mraible
PRO
11
4.6k
Building an army of robots
kneath
299
40k
What’s in a name? Adding method to the madness
productmarketing
11
1.5k
Documentation Writing (for coders)
carmenhchung
48
2.5k
Cheating the UX When There Is Nothing More to Optimize - PixelPioneers
stephaniewalter
268
11k
Embracing the Ebb and Flow
colly
73
3.3k
Transcript
The Problem
None
Server Node 1 Server Node 2
Node A Node B [User] [User] [User] [] [] [User]
User connects User disconnects
There's no global time
Node A Node B [User] [User] [User] [] [] [User]
User connects User disconnects
Node A Node B [User] [User] [User] [] [] [User]
User connects User disconnects
Node A Node B
P.track(self, "users", "U1", %{})
P.track(self, "users", "U1", %{}) P.list("users") %{"U1" %{metas: [%{phx_ref: "…"}]}}
P.track(self, "users", "U1", %{}) P.list("users") P.track(self, "users", "U2", %{}) %{"U1"
%{metas: [%{phx_ref: "…"}]}}
P.track(self, "users", "U1", %{}) P.list("users") P.track(self, "users", "U2", %{}) P.list("users")
%{"U1" %{metas: [%{phx_ref: "…"}]}, "U2" %{metas: [%{phx_ref: "…"}]}} %{"U1" %{metas: [%{phx_ref: "…"}]}}
P.track(self, "users", "U1", %{}) P.list("users") P.track(self, "users", "U2", %{}) P.list("users")
%{"U1" %{metas: [%{phx_ref: "…"}]}, "U2" %{metas: [%{phx_ref: "…"}]}} P.track(self, "users", "U1", %{}) P.untrack(self, "users", "U1") %{"U1" %{metas: [%{phx_ref: "…"}]}}
P.track(self, "users", "U1", %{}) P.list("users") P.track(self, "users", "U2", %{}) P.list("users")
%{"U1" %{metas: [%{phx_ref: "…"}]}, "U2" %{metas: [%{phx_ref: "…"}]}} P.track(self, "users", "U1", %{}) P.untrack(self, "users", "U1") P.list("users") %{"U1" %{metas: [%{phx_ref: "…"}]}, "U2" %{metas: [%{phx_ref: "…"}]}} P.list("users") %{"U1" %{metas: [%{phx_ref: "…"}]}, "U2" %{metas: [%{phx_ref: "…"}]}} %{"U1" %{metas: [%{phx_ref: "…"}]}}
CRDTs The science behind Phoenix Presence Maciej Kaszubowski
Conflict-free Replicated Data Type
Alternatives
• Single source of truth (DB) • Consensus algorithm •
Resolving conflicts manually
Why CRDTs?
Eventually consistent Highly available Easy to use
Eventually consistent Highly available Easy to use Hard to create
:(
Features
1. Commutative 2. Associative 3. Idempotent x y = y
x (x y) z = x (y z) x x = x
Server Node 1 Server Node 2 Server Node 3
Client Client Client Client Client Client Client Client Client Server
Examples
Counters
Node A Node B +5 5 8 -2 3 +5
User connects User disconnects 0 0 5 3 8
Node A Node B +5 5 8 -2 8 +5
User connects User disconnects 0 0 5 3 13 10
G-Counter Grow-only counter
Node 2: 3 Value=8 Node 1: 5 Node 3: 1
Merge
Node 2: 3 Value=9 Node 1: 6 Node 3: 1
+1 Merge
PN-Counter Positive-Negative Counter
Node 2: P=2 N=2 Value=7 Node 1: P=5 N=2 Node
3: P=4 N=0 3 0 4 Merge
Node 2: P=2 N=2 Value=6 Node 1: P=5 N=3 Node
3: P=4 N=0 2 0 4 +1 Merge
Node 2: P=2 N=2 Value=8 Node 1: P=5 N=3 Node
3: P=6 N=0 2 0 6 +2 +1 Merge
Sets
Node A Node B [User] [User] [User] [] [] [User]
User connects User disconnects
G-Set Grow-only set
Node 2: [1,2] Value=[1,2,3,4] Node 1: [1] Node 3: [3,4]
Merge
Node 2: [1,2] Value=[1,2,3,4,5] Node 1: [1,5] Node 3: [3,4]
Merge
2P-Set Two-phase set
Node 2: [1,2],[] Value=[1,2,3,4] Node 1: [1],[] Node 3: [3,4],[]
Merge
Node 2: [1,2],[] Value=[1,2,3,4] Node 1: [1],[] Node 3: [3,4],[]
Merge G-Set for adds
Node 2: [1,2],[] Value=[1,2,4] Node 1: [1],[] Node 3: [3,4],[3]
Merge G-Set for removals
Elements cannot be re-added
Removes win
Node A Node B [ ] Add Remove [1] [
] [1]
Node A Node B [ ] [1] Add Remove [1]
[1] [ ] [1] [ ] [1]
Node A Node B [ ] [1] Add Remove [1]
[1] [ ] [1] [ ] [1]
Node A Node B [ ] [1] [1] Add Remove
[1] [1] [1] [ ] [1] [1] [1] [ ] [1]
OR-Set Observed-remove set
Node A Node B [ ] Add Remove [{A,1}] [
] [{A,1}]
Node A Node B [ ] [ ] Add Remove
[{A,1}] [{A,1}] [ ] [ ] [{A,1}] [{A,1}, ]
Node A Node B [ ] [ 1 ] Add
Remove [{A,1}] [{A,1}] [ ] [ ] [{A,1}] [{A,1},{A,2}]
Node A Node B [ ] [ 1 ] Add
Remove [{A,1}] [{A,1}] [ ] [ ] [{A,1}] [{A,1},{A,2}]
Node A Node B [ ] [ 1 ] Add
Remove [{A,1}] [{A,1}] [ ] [ ] [{A,1}] [{A,1},{A,2}] [ 1 ] [{A,1},{A,2}] [{A,1},{A,2}] [ 1 ]
Node A Node B [ ] [ 1 ] Add
Remove [{A,1}] [{A,1}] [ ] [ ] [{A,1}] [{A,1},{A,2}] [ 1 ] [{A,1},{A,2}] [{A,1},{A,2}] [ 1 ] [A] [A]
Add 1000 Remove 1000 Add Remove …
ORSWOT Observed-remove set without tombstones
None
None
Use Cases
None
None
None
None
• Load balancing / routing • Mobile clients synchronisation •
Temporary data on the servers • Avoiding work duplication • Collaborative editing
None
lasp-lang.readme.io
Summary
You're (almost) always designing a distributed system
Think about failures
Choose the correct tool for the job
References • https://medium.com/@istanbul_techie/a-look-at-conflict-free-replicated-data- types-crdt-221a5f629e7e • http://basho.com/posts/technical/distributed-data-types-riak-2-0/ • http://highscalability.com/blog/2014/10/13/how-league-of-legends-scaled- chat-to-70-million-players-it-t.html •
https://hal.inria.fr/inria-00609399v1/document • https://developers.soundcloud.com/blog/roshi-a-crdt-system-for- timestamped-events
Thanks!