# `Runic.Runner.Store.Mnesia`
[🔗](https://github.com/zblanco/runic/blob/main/lib/runic/runner/store/mnesia.ex#L1)

Mnesia-backed persistence adapter for the Runner.

Uses Erlang/OTP's built-in Mnesia database for workflow log storage.
Provides persistence across VM restarts (via `disc_copies`) and
distributed storage across Erlang clusters.

## Usage

    children = [
      {Runic.Runner.Store.Mnesia, runner_name: MyApp.Runner, disc_copies: true},
      {Runic.Runner,
       name: MyApp.Runner,
       store: Runic.Runner.Store.Mnesia,
       store_opts: [disc_copies: true]}
    ]

## Options

  * `:runner_name` — (required) the Runner name, used to derive the Mnesia table name
  * `:disc_copies` — when `true` (default), persists to disk on this node.
    Set to `false` for RAM-only tables (faster, lost on VM restart).
  * `:nodes` — list of nodes for distributed tables.
    Defaults to `[node()]`.

## Mnesia Schema

If Mnesia has not been initialized with a schema directory on this node,
one will be created automatically. For production use, configure the
Mnesia directory via the `:mnesia` application env:

    config :mnesia, dir: ~c"/var/data/mnesia/#{node()}"

## Distributed Operation

For multi-node Mnesia clusters, ensure `:mnesia.change_config(:extra_db_nodes, nodes)`
is called before starting the Runner, or pass `:nodes` in store opts.

## Stream Semantics

Supports event-sourced `append/3` and `stream/2` via a second Mnesia table
(`*EventStream`) with `{workflow_id, sequence}` compound keys for ordered
event retrieval.

## Design Notes

  * Write operations use `:mnesia.transaction/1` for ACID guarantees.
  * Read operations use `:mnesia.dirty_read/2` — no transaction overhead,
    eventually consistent during concurrent writes (sufficient for workflow
    log reads, which are dominated by the owning Worker process).
  * `checkpoint/3` delegates to `save/3` — Mnesia's transaction log already
    provides write-ahead durability.

# `child_spec`

Returns a specification to start this module under a supervisor.

See `Supervisor`.

# `start_link`

---

*Consult [api-reference.md](api-reference.md) for complete listing*