scala-dvvset

A Dotted Version Vector Sets implementation in Scala

Scala version of the Dotted Version Vector Sets Erlang reference implementation. This data structure used in distributed systems to track the causality relationships between events.

Usage

Creating a new version without history

import dvvset._

val replicaA = Replica("a")
val dvv = Clock.from("v1")
  .update(replicaA)

println(dvv) // Clock([(replicaA, 1, [v1])], [])

Create a new version with history

import dvvset._

val replicaA = Replica("a")
val dvv0 = Clock.from("v1").update(replica)

// Create a new version with history
val dvv1 = Clock.from(dvv0.version, "v2")
  .update(dvv0, replica)

println(dvv1) // Clock([(replicaA, 2, [v2])], [])

Conflicting versions

import dvvset._
val replica = Replica("a")

val dvv0 = Clock.from("v1").update(replica)

val dvv1 = Clock.from(dvv0.version, "v2")
    .update(dvv0, replica)

// Create a new version with old history and updated with a new version
val dvv2 = Clock.from(dvv0.version, "v3")
    .update(dvv1, replica)

println(dvv1) // Clock([(replicaA, 2, [v2])], [])
println(dvv2) // Clock([(replicaA, 3, [v3, v2])], [])

Real world usage

There is also a simple KeyValue store implementation using the DVVSet in demo/src/main/scala/demo/KeyValueStore.scala.

import dvvset._
import demo.KeyValueStore
import demo.Node

val replica = Node("a")
val store = new KeyValueStore[String](replica)
val u1 = store.put("key", "v1")

// There is only one value for that Key
assert(store.get("key").contains(Just("v1", VersionVector(List(replica -> 1)))))

// Update the value with a new version
val u2 = store.put("key", "v2", u1.version)

// The value is updated with latest version
assert(store.get("key").contains(Just("v2", VersionVector(List(replica -> 2)))))

// Updating the key with old version
val u3 = store.put("key", "v3", u1.version)

// Now there is a conflict with the old version
assert(store.get("key").contains(Conflict(Set("v3", "v2"), VersionVector(List(replica -> 3)), withDeleted = false)))

// Update the value one more time with the last version (Resolving the conflict)
val u4 = store.put("key", "v4", u3.version)

// The value is updated with latest version without conflict
assert(store.get("key").contains(Just("v4", VersionVector(List(replica -> 4)))))

// Delete the key
val d1 = store.delete("key", u4.version)

// The key is deleted
assert(store.get("key").isEmpty)

alirezameskin / scala-dvvset