Enki

Enki is a simple persistable message queue that utilises Mnesia.

Why Enki?

Enki phonetically sounds like a shortened term for Enqueue. It's also the name of the Sumerian God of Creation (cue rock music!).

Installation

Add the following to your deps in your mix.exs file.

def deps do
  [
    {:enki, "~> 0.2"}
  ]
end

Then, add :enki to your list of applications.

def application do
  [
    extra_applications: [:enki, ...],
    mod: {YourApp, []}
  ]
end

Configuration

There are several options to configure Enki.

config :enki,
  ttf: 5000,           # number of milliseconds to keep message in-flight
  file_persist: false  # determines whether to use Mnesia's file persistences

Usage

Enki is a simple queue. It doesn't enforce FIFO (first in first out) and so isn't a strict queue, but it is a great little tool for maintaining data you will want to consumer over time, such as where queues are typically implmeneted.

Enki provides in-flight management. Thus, when dequeuing a value, if it is not ack'd within the duration of the ttf (time-to-flight) setting, the value will be replaced into the queue.

To use, create a module to use as a message:

defmodule MyApp.MyModel do
  use Enki.Message,
    attributes: [:attr1, :attr2]
end

This replaces any equivelent struct, so do not create is as:

defmodule MyApp.MyModel do
  defstruct attr1, attr2
end

The use option ensures the model includes meta needed by Enki.

Next, you need to initialise the queue. You can initialise multiple queues at once, if needed:

Enki.init([MyApp.MyModel])

Once initialised, you can then enqueue and dequeue as needed:

Enki.enq(%MyModel{attr1: 1, attr2: 2})
%MyModel{enki_id: id, attr1: 1, attr2: 2} = Enki.deq(MyModel)
# ... process data
Enki.ack(id)

The ack must be called within the given ttf period (in milliseconds). Otherwise, the message will be re-queued.

Documentation

Documentation can be found at https://hexdocs.pm/enki.