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Clarify a few items in the docs #15628

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Oct 9, 2024
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Clarify a few items in the docs #15628

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c6e9ec4
add concurrency limit notes
discdiver Oct 9, 2024
58efc1c
edit for vale to pass formatting
discdiver Oct 9, 2024
f825348
note what max_workers param does in task runner example
discdiver Oct 9, 2024
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17 changes: 14 additions & 3 deletions docs/3.0/develop/global-concurrency-limits.mdx
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Expand Up @@ -52,13 +52,13 @@ To implement rate limiting, you can configure "slot decay", which determines how

When you set up a concurrency limit with slot decay:
1. Each time a slot is occupied, it becomes unavailable for other tasks to use.
2. The slot eventually becomes available again over time, based on the slot decay rate (i.e. `slot_decay_per_second`).
2. The slot eventually becomes available again over time, based on the slot decay rate (with `slot_decay_per_second`).
3. This creates a "rate limiting" effect, limiting how often slots can be used.

To configure slot decay, set the `slot_decay_per_second` parameter when creating or updating a concurrency limit. This value determines how quickly slots refresh:

- A higher value (e.g., 5.0) means slots refresh quickly. Tasks can run more frequently, but with short pauses between them.
- A lower value (e.g., 0.1) means slots refresh slowly. Tasks run less frequently, with longer pauses between them.
- A higher value (for example, 5.0) means slots refresh quickly. Tasks can run more frequently, but with short pauses between them.
- A lower value (for example, 0.1) means slots refresh slowly. Tasks run less frequently, with longer pauses between them.

For example:

Expand Down Expand Up @@ -362,3 +362,14 @@ async def main():
if __name__ == "__main__":
asyncio.run(main())
```

## Other ways to limit concurrency

In addition to global concurrency limits, Prefect provides several other ways to limit concurrency for fine-grained control.

Unlike global concurrency limits, which are a more general way to control concurrency for any Python-based operation, the following concurrency limit options are specific to Prefect objects:

- [Work pool flow run concurrency limits](/3.0/deploy/infrastructure-concepts/work-pools#manage-concurrency)
- [Work queue flow run concurrency limits](/3.0/deploy/infrastructure-concepts/work-pools#queue-concurrency-limits)
- [Deployment flow run concurrency limits](/3.0/deploy/index#concurrency-limiting)
- [Task run concurrency limits](/3.0/develop/task-run-limits)
6 changes: 2 additions & 4 deletions docs/3.0/develop/task-run-limits.mdx
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Expand Up @@ -10,11 +10,9 @@ Task run concurrency limits use [task tags](#tags). You can specify an optional
task runs in a `Running` state for tasks with a given tag.

<Tip>
Tag-based task concurrency is different from [Global Concurrency Limits](/3.0/develop/global-concurrency-limits), though they can be used to achieve similar outcomes. Global Concurrency Limits are a more general way to control concurrency for any python-based operation, whereas tag-based concurrency limits are specific to Prefect tasks.
Tag-based task concurrency is different from [Global concurrency limits](/3.0/develop/global-concurrency-limits), though they can be used to achieve similar outcomes. Global concurrency limits are a more general way to control concurrency for any Python-based operation, whereas tag-based concurrency limits are specific to Prefect tasks.
</Tip>



If a task has multiple tags, it will run only if **_all_** tags have available concurrency.

Tags without specified concurrency limits are treated as unlimited. Setting a tag's concurrency limit to 0 causes immediate abortion of any task runs with that tag, rather than delaying them.
Expand All @@ -30,7 +28,7 @@ and instructs the client to try entering a `Running` state again in 30 seconds
### Configure concurrency limits

<Tip>
**Flow run concurrency limits are set at a work pool and/or work queue level**
**Flow run concurrency limits are set at a work pool, work queue, or deployment level**

While task run concurrency limits are configured through tags (as shown below), [flow run concurrency limits](/3.0/develop/global-concurrency-limits) are configured through work pools and/or work queues.
</Tip>
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1 change: 1 addition & 0 deletions docs/3.0/develop/task-runners.mdx
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Expand Up @@ -79,6 +79,7 @@ If you don't specify a task runner for a flow and you call a task with `.submit(
Prefect uses the default `ThreadPoolTaskRunner`.
</Tip>

The `max_workers` parameter of the `ThreadPoolTaskRunner` controls the number of threads that the task runner will use to execute tasks concurrently.

## Access results from submitted tasks

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