DeltaCrdt

DeltaCrdt implements a key/value store using concepts from Delta CRDTs, and relies on MerkleMap for efficient synchronization. It implements also GCounter and PNCounter

There is a (slightly out of date) introductory blog post and the (very much up to date) official documentation on hexdocs.pm is also very good.

The following papers have been used to implement this library:

• Delta State Replicated Data Types – Almeida et al. 2016
• Efficient Synchronization of State-based CRDTs – Enes et al. 2018

Usage

Documentation can be found on hexdocs.pm.

Here's a short example to illustrate adding an entry to a map:

# start 2 Delta CRDTs
{:ok, crdt1} = DeltaCrdt.start_link(DeltaCrdt.Causal, DeltaCrdt.AWLWWMap)
{:ok, crdt2} = DeltaCrdt.start_link(DeltaCrdt.Causal, DeltaCrdt.AWLWWMap)

# make them aware of each other
DeltaCrdt.set_neighbours(crdt1, [crdt2])

# show the initial value
DeltaCrdt.read(crdt1)
%{}

# add a key/value in crdt1
DeltaCrdt.mutate(crdt1, :add, ["CRDT", "is magic!"])

# read it after it has been replicated to crdt2
DeltaCrdt.read(crdt2)
%{"CRDT" => "is magic!"}

#start 2 PNCounter
{:ok, crdt3} = DeltaCrdt.start_link(DeltaCrdt.NamedCrdt,DeltaCrdt.PNCounter)
{:ok, crdt4} = DeltaCrdt.start_link(DeltaCrdt.NamedCrdt,DeltaCrdt.PNCounter)

DeltaCrdt.set_neighbours(crdt3, [crdt4])

DeltaCrdt.read(crdt4)
0

DeltaCrdt.mutate(crdt3, :inc, [5])

DeltaCrdt.read(crdt4)
5

DeltaCrdt.mutate(crdt3, :dec, [3])

DeltaCrdt.read(crdt4)
2

#start 2 GCounter
{:ok, crdt5} = DeltaCrdt.start_link(DeltaCrdt.NamedCrdt,DeltaCrdt.GCounter)
{:ok, crdt6} = DeltaCrdt.start_link(DeltaCrdt.NamedCrdt,DeltaCrdt.GCounter)

DeltaCrdt.set_neighbours(crdt5, [crdt6])

DeltaCrdt.read(crdt6)
0

DeltaCrdt.mutate(crdt5, :inc, [5])

DeltaCrdt.read(crdt6)
5

Telemetry metrics

DeltaCrdt publishes the metric [:delta_crdt, :sync, :done].

Installation

The package can be installed by adding delta_crdt to your list of dependencies in mix.exs:

def deps do
  [
    {:delta_crdt, "~> 0.5.0"}
  ]
end