# `Rheo.Backend.ETS`
[🔗](https://github.com/thanos/rheo/blob/v1.0.0/lib/rheo/backend/ets.ex#L1)

In-memory ETS implementation of `Rheo.Backend`.

Always available (no optional dependency). Prefer for tests, Livebook, local
demos, and ephemeral apps. Prefer Mongo, Ecto, Redis, or Mnesia when events
must survive process or node restart.

Prefer the `Rheo` facade for application code. The opaque handle is this
process's registered name (default `Rheo.ETS`), started via `child_spec/1`.

## When to use

  * Unit and contract tests that need a real backend without external services
  * Livebook / Notebook prototypes
  * Single-node apps where loss on restart is acceptable

Do **not** use when durability or multi-node lease arbitration is required
(`durable: false`, `distributed: false`).

## Capabilities

  * `durable: false` — tables die with the owner GenServer / node
  * `distributed: false` — not shared across BEAM nodes
  * `batch_writes: true`, `ordered_range_scan: true`
  * `replay: true`, `partitions: true`, `contiguous_frontier: true`
  * `secondary_indexes: false` — `query/2` filters in-process
  * `notifications: false`, `atomic_compare_and_set: false`

## Tables

Per-instance protected ETS tables owned by this GenServer:

    streams / events / groups / deliveries
    event_ids / delivery_by_seq / open_deliveries

## Options

  * `:name` — handle / process name (default `default_handle/0`)

## Supervision example

    children = [
      {Rheo, name: MyRheo, backend: Rheo.Backend.ETS}
    ]

Named handle:

    children = [
      {Rheo, name: MyRheo, backend: {Rheo.Backend.ETS, name: MyRheo.ETS}}
    ]

Callback semantics are documented on `Rheo.Backend`.

# `child_spec`

```elixir
@spec child_spec(keyword()) :: Supervisor.child_spec()
```

Child spec for the ETS GenServer (backend handle).

## Arguments

  * `opts` — keyword options:
    * `:name` — handle / process name (default `default_handle/0`)

## Examples

    iex> spec = Rheo.Backend.ETS.child_spec(name: :demo_ets)
    iex> {spec.id, elem(spec.start, 0), spec.type}
    {{Rheo.Backend.ETS, :demo_ets}, Rheo.Backend.ETS, :worker}

## Returns

A supervisor child spec map.

# `default_handle`

```elixir
@spec default_handle() :: atom()
```

Default ETS handle name for the `Rheo` instance.

## Examples

    iex> Rheo.Backend.ETS.default_handle()
    Rheo.ETS

## Returns

A process name atom (`Rheo.ETS`).

---

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