# `Slap.Streams.Cluster`
[🔗](https://github.com/mjrusso/slap/blob/slap_streams-v0.3.0/slap_streams/lib/slap/streams/cluster.ex#L1)

The shards that hold the streams, a `Slap.Cluster`. Each shard allocates
stream ids and supervises one process per active stream.

Run one instance of this built-in cluster per VM. It can own many shards
and participate in a cluster across VMs. `Slap.Streams.Metrics` reports
node-wide metrics for this instance.

To configure a cluster under your application's name, define a module
with `use Slap.Streams.Cluster, otp_app: :my_app`, supervise that module
in place of `Slap.Streams.Cluster`, and pass `cluster: MyApp.StreamsCluster`
to Streams operations and `Slap.Streams.HTTP.Router`. Run one Streams
cluster per VM; metrics and the router's request-body budget are node-wide.

Configure it like any `Slap.Cluster`:

    config :slap_streams, Slap.Streams.Cluster,
      store: {:url, "s3://streams/db", aws_endpoint: "https://rustfs:9000"},
      shards: 8

Durable appends wait for SlateDB's next WAL flush. This cluster sets
`flush_interval` to 10 ms, the value used by the Durable Streams design;
SlateDB's default is 100 ms. Other settings leave the 10 ms default intact.
The README describes the latency and object-store request trade-off.

Service settings go in `child_options:` at start. See
`child_option_keys/0` for the accepted keys. Values are positive integers
in milliseconds for timeouts and intervals, bytes for byte limits, and
entries for `:deleter_page`. `:max_fork_copy_bytes` and `:fork_copy_grace`
may also be zero.

# `__using__`
*macro* 

Defines a Streams cluster under the given `:otp_app`.

# `assignments`

Where every shard is. See `Slap.Cluster.assignments/1`.

# `call`

Runs a function with a shard's context. See `Slap.Cluster.call/4`.

# `child_option_keys`

```elixir
@spec child_option_keys() :: [atom()]
```

Returns the accepted `:child_options` keys for a Streams cluster.

# `local_shards`

The shards open on this node.

# `lookup`

Where a shard is. See `Slap.Cluster.lookup/2`.

# `shard_for`

The shard for a placement key. See `Slap.Cluster.shard_for/2`.

# `start_link`

Starts the cluster. `opts` override the application environment, which
overrides the `:defaults` given to `use Slap.Cluster`.

# `stop`

Stops the cluster on this node, closing its shards.

# `via`

A name for a per-shard process. See `Slap.Cluster.via/3`.

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