# Mnesiac
[](https://travis-ci.org/beardedeagle/mnesiac) [](https://codecov.io/gh/beardedeagle/mnesiac) [](https://hex.pm/packages/mnesiac) [](https://hex.pm/packages/mnesiac)
Mnesia auto clustering made easy!
Docs can be found at [https://hexdocs.pm/mnesiac](https://hexdocs.pm/mnesiac).
**_NOTICE:_** Mnesiac, while stable, is still considered pre `1.0`. This means the API can, and may, change at any time. Please ensure you review the docs and changelog prior to updating.
**_NOTICE:_** Mnesiac allows a significant amount of freedom with how it behaves. This allows you to customize Mnesiac to suit your needs. However, this also allows for a fair amount of foot gunning. Please ensure you've done your due diligence when using this library, or Mnesia itself for that matter. It isn't a silver bullet, and it shouldn't be treated as one.
## Installation
Simply add `mnesiac` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:mnesiac, "~> 0.3"}
]
end
```
Edit your app's config.exs to add the list of Mnesia stores:
```elixir
config :mnesiac,
stores: [Mnesiac.ExampleStore, ...],
schema_type: :disc_copies, # defaults to :ram_copies
table_load_timeout: 600_000 # milliseconds, default is 600_000
```
Then add `mnesiac` to your supervision tree:
- **_EXAMPLE:_** With `libcluster` using the `Cluster.Strategy.Epmd` strategy:
```elixir
...
topology = Application.get_env(:libcluster, :topologies)
hosts = topology[:myapp][:config][:hosts]
children = [
{Cluster.Supervisor, [topology, [name: MyApp.ClusterSupervisor]]},
{Mnesiac.Supervisor, [hosts, [name: MyApp.MnesiacSupervisor]]},
...
]
...
```
- **_EXAMPLE:_** Without `libcluster`:
```elixir
...
children = [
{
Mnesiac.Supervisor,
[
[:"test01@127.0.0.1", :"test02@127.0.0.1"],
[name: MyApp.MnesiacSupervisor]
]
},
...
]
...
```
## Usage
### Table creation
Create a table store, `use Mnesiac.Store`, and add it to your app's config.exs.
All stores **_MUST_** implement its own `store_options/0`, which returns a keyword list of store options.
There are three optional callbacks which can be implemented:
- `init_store/0`, which allows users to implement custom store initialization logic. Triggered by Mnesiac.
- `copy_store/0`, which allows users to implement a custom call to copy a store. Triggered by Mnesiac.
- `resolve_conflict/1`, which allows a user to implement logic when Mnesiac detects a store with records on both the local and remote Mnesia cluster node. Triggered by Mnesiac. Default is to do nothing.
**_MINIMAL EXAMPLE:_**:
```elixir
defmodule MyApp.ExampleStore do
@moduledoc """
Provides the structure of ExampleStore records for a minimal example of Mnesiac.
"""
use Mnesiac.Store
import Record, only: [defrecord: 3]
@doc """
Record definition for ExampleStore example record.
"""
Record.defrecord(
:example,
__MODULE__,
id: nil,
topic_id: nil,
event: nil
)
@typedoc """
ExampleStore example record field type definitions.
"""
@type example ::
record(
:example,
id: String.t(),
topic_id: String.t(),
event: String.t()
)
@impl true
def store_options,
do: [
record_name: __MODULE__,
attributes: example() |> example() |> Keyword.keys(),
index: [:topic_id],
ram_copies: [node()]
]
end
```
### Clustering
If you are using `libcluster` or another clustering library, ensure that the clustering library starts before `mnesiac`. That's all, you don't need to do anything else.
If you are not using `libcluster` or similar clustering libraries then:
- When a node joins to an erlang/elixir cluster, run the `Mnesiac.init_mnesia/1` function on the **_new node_**. This will initialize and copy the store contents from the other online nodes in the Mnesia cluster.
## Development
Ensure you have the proper language versions installed. To do this, an `asdf` tools file has been provided. Run the following:
```shell
git clone https://github.com/beardedeagle/mnesiac.git
git checkout -b MyFeature
asdf install
mix local.hex --force
mix local.rebar --force
mix deps.get --force
mix deps.compile --force
mix compile --force
```
**_NOTICE:_** You can find the `asdf` tool [here][1].
## Testing
Before you run any tests, ensure that you have cleaned up Mnesia:
```shell
mix purge.db
```
Test results and coverage reports are generated by running the following:
```shell
mix coveralls.html --trace --slowest 10 --no-start
```
## Notice
This library was built standing on the shoulders of giants. A big thanks goes out to Mustafa Turan. The original library this was forked from can be found here: <https://github.com/mustafaturan/mnesiam>.
Happy coding!
[1]: https://github.com/asdf-vm/asdf
