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56 lines
2.0 KiB
Plaintext
56 lines
2.0 KiB
Plaintext
---
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id: 'function-background-tasks'
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title: 'Background Tasks'
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description: 'How to run background tasks in an Edge Function outside of the request handler'
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subtitle: 'How to run background tasks in an Edge Function outside of the request handler'
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tocVideo: 'rSKBTJxG9VA'
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---
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Edge Function instances can process background tasks outside of the request handler. Background tasks are useful for asynchronous operations like uploading a file to Storage, updating a database, or sending events to a logging service. You can respond to the request immediately and leave the task running in the background.
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### How long a background task can run
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A background task can run until the Edge Function instance hits its wall-clock limit or reaches CPU/Memory limit. Check [limits](/docs/guides/functions/limits) for current caps.
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### Example
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Here's an example of defining a background task using a custom event.
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```ts
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// Define a custom event type for the background task.
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class MyBackgroundTaskEvent extends Event {
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readonly taskPromise: Promise<Response>
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constructor(taskPromise: Promise<Response>) {
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super('myBackgroundTask')
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this.taskPromise = taskPromise
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}
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}
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globalThis.addEventListener('myBackgroundTask', async (event) => {
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const res = await (event as MyBackgroundTaskEvent).taskPromise
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console.log(await res.json())
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})
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Deno.serve(async (req) => {
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const fetchPromise = fetch('https://httpbin.org/json')
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const event = new MyBackgroundTaskEvent(fetchPromise)
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globalThis.dispatchEvent(event)
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return new Response('ok')
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})
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```
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### Testing background tasks locally
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When testing Edge Functions locally with Supabase CLI, the instances are terminated automatically after a request is completed. This will prevent background tasks from running to completion.
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To prevent that, you can update the `supabase/config.toml` with the following settings:
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```toml
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[edge_runtime]
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policy = "per_worker"
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```
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When running with `per_worker` policy, Function won't auto-reload on edits. You will need to manually restart it by running `supabase functions serve`.
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