# Class: Pool

Extends: `undici.Dispatcher`

A pool of [Client](/docs/docs/api/Client.md) instances connected to the same upstream target.

Requests are not guaranteed to be dispatched in order of invocation.

## `new Pool(url[, options])`

Arguments:

* **url** `URL | string` - It should only include the **protocol, hostname, and port**.
* **options** `PoolOptions` (optional)

### Parameter: `PoolOptions`

Extends: [`ClientOptions`](/docs/docs/api/Client.md#parameter-clientoptions)

* **factory** `(origin: URL, opts: Object) => Dispatcher` - Default: `(origin, opts) => new Client(origin, opts)`
* **connections** `number | null` (optional) - Default: `null` - The number of `Client` instances to create. When set to `null`, the `Pool` instance will create an unlimited amount of `Client` instances.
* **clientTtl** `number | null` (optional) - Default: `null` - The amount of time before a `Client` instance is removed from the `Pool` and closed.   When set to `null`, `Client` instances will not be removed or closed based on age.

> [!NOTE]
> `Pool` inherits all [`ClientOptions`](/docs/docs/api/Client.md#parameter-clientoptions), including `allowH2` (default `true`) and `maxConcurrentStreams` (default `100`). With the unlimited default of `connections`, `Pool` will open a new `Client` — and therefore a new TCP/TLS socket — per concurrent dispatch, which defeats HTTP/2 multiplexing on a shared session. To benefit from h2 multiplexing on a single session, cap `connections` (e.g. `connections: 1`) so that concurrent requests share a session up to `maxConcurrentStreams`.

## Instance Properties

### `Pool.closed`

Implements [Client.closed](/docs/docs/api/Client.md#clientclosed)

### `Pool.destroyed`

Implements [Client.destroyed](/docs/docs/api/Client.md#clientdestroyed)

### `Pool.stats`

Returns [`PoolStats`](/docs/docs/api/PoolStats.md) instance for this pool.

## Instance Methods

### `Pool.close([callback])`

Implements [`Dispatcher.close([callback])`](/docs/docs/api/Dispatcher.md#dispatcherclosecallback-promise).

### `Pool.destroy([error, callback])`

Implements [`Dispatcher.destroy([error, callback])`](/docs/docs/api/Dispatcher.md#dispatcherdestroyerror-callback-promise).

### `Pool.connect(options[, callback])`

See [`Dispatcher.connect(options[, callback])`](/docs/docs/api/Dispatcher.md#dispatcherconnectoptions-callback).

### `Pool.dispatch(options, handler)`

Implements [`Dispatcher.dispatch(options, handler)`](/docs/docs/api/Dispatcher.md#dispatcherdispatchoptions-handler).

### `Pool.pipeline(options, handler)`

See [`Dispatcher.pipeline(options, handler)`](/docs/docs/api/Dispatcher.md#dispatcherpipelineoptions-handler).

### `Pool.request(options[, callback])`

See [`Dispatcher.request(options [, callback])`](/docs/docs/api/Dispatcher.md#dispatcherrequestoptions-callback).

### `Pool.stream(options, factory[, callback])`

See [`Dispatcher.stream(options, factory[, callback])`](/docs/docs/api/Dispatcher.md#dispatcherstreamoptions-factory-callback).

### `Pool.upgrade(options[, callback])`

See [`Dispatcher.upgrade(options[, callback])`](/docs/docs/api/Dispatcher.md#dispatcherupgradeoptions-callback).

## Instance Events

### Event: `'connect'`

See [Dispatcher Event: `'connect'`](/docs/docs/api/Dispatcher.md#event-connect).

### Event: `'disconnect'`

See [Dispatcher Event: `'disconnect'`](/docs/docs/api/Dispatcher.md#event-disconnect).

### Event: `'drain'`

See [Dispatcher Event: `'drain'`](/docs/docs/api/Dispatcher.md#event-drain).
