@Marvin when I manually interrupt a flow or it crashes, any acquired concurrency limit isn't released blocking subsequent executions. What are the ways I can address this?

To address the issue of concurrency limits not being released when a flow is manually interrupted or crashes in Prefect 3.x, you can consider the following approaches: 1. Use Prefect CLI or API: You can manually release concurrency limits using the Prefect CLI or API. This can be done by deleting the concurrency limit set on a specific tag. For example, using the Prefect CLI, you can execute:

sh
   prefect concurrency-limit delete --tag <tag_name>

You can also use the Prefect API to manage concurrency limits programmatically. Refer to the Prefect concurrency limits documentation for more details. 2. Handle Flow Interruptions: Ensure that your flow and task logic include mechanisms for handling interruptions gracefully. This might involve using try-except blocks to catch exceptions and release resources or limits if an error occurs. 3. Monitor and Debug: Regularly monitor your flows and tasks to identify any patterns or specific tasks that frequently cause interruptions. Debugging these areas might prevent future issues. 4. Check for Known Issues: There are known issues related to concurrency slots not being released properly when tasks are interrupted or flow is deleted. You can track the progress or workarounds for such issues on GitHub, like this issue. By implementing these strategies, you can mitigate the impact of concurrency limits not being released during interruptions and ensure smoother operation of your Prefect flows.

@Marvin when a flow crashed because it's OOM killed for instance, is there a hook I can use from the flow itself to clear the concurrency limits right before the flow is effectively interrupted?

In Prefect 3.x, you can use hooks to execute specific logic when a flow enters certain states. For handling cases where a flow crashes, you can utilize the

on_crashed_hooks

. These hooks allow you to perform actions right before the flow is effectively interrupted, such as clearing concurrency limits. Here's a basic example of how you might set up a hook in your flow:

python
from prefect import flow, get_client

async def clear_concurrency_limits():
    async with get_client() as client:
        # Replace 'your_tag' with the actual tag used for your concurrency limit
        await client.delete_concurrency_limit(tag='your_tag')

@flow(on_crashed_hooks=[clear_concurrency_limits])
def my_flow():
    # Your flow logic here
    pass

In this setup, the

clear_concurrency_limits

function will be called if the flow crashes, allowing you to clean up any concurrency limits that might block subsequent runs. This relies on the

on_crashed_hooks

feature, which you can find in the Prefect source code. For more details on concurrency limits and handling flow states, refer to the Prefect documentation.

@Marvin I want to use the python sdk to programmatically reset slots for global concurrency limits by names. Can you help out?

To programmatically reset slots for global concurrency limits using the Prefect Python SDK, you can utilize the

PrefectClient

class from the

prefect.client.orchestration

module. Here's a basic example of how you might achieve this:

python
from prefect.client.orchestration import PrefectClient

async def reset_global_concurrency_limit(limit_name: str):
    async with PrefectClient() as client:
        # Assuming a method exists to reset slots by name
        await client.reset_global_concurrency_limit(name=limit_name)

# Example usage
import asyncio

asyncio.run(reset_global_concurrency_limit("your_limit_name"))

This example assumes that a method exists within the

PrefectClient

to reset global concurrency limits by name. If such a method is not directly available, you might need to explore the client methods related to concurrency limits or refer to the Prefect documentation for any updates on API capabilities.

@Marvin Can you point me to the code or the documentation listing the available methods for interacting with global concurrency limits?

For interacting with global concurrency limits in Prefect, you can make use of the Prefect CLI and API. The documentation provides several commands for managing concurrency limits: 1. Creating a Concurrency Limit: Use the

prefect gcl create

command. You must specify a

--limit

argument and can optionally specify a

--slot-decay-per-second

and

--disable

argument. 2. Inspecting a Concurrency Limit: Use the

prefect gcl inspect

command to view the details of an existing concurrency limit. 3. Updating a Concurrency Limit: Use the

prefect gcl update

command to modify existing limits, including

--limit

,

--slot-decay-per-second

,

--enable

, and

--disable

. 4. Deleting a Concurrency Limit: Use the

prefect gcl delete

command to remove an existing concurrency limit. For more detailed information and to explore all available commands and options, you can check the global concurrency limits documentation. If you need to use these operations programmatically, consider looking into the

PrefectClient

class from the

prefect.client.orchestration

module, though specific methods for resetting slots might not be explicitly documented. You can explore the Prefect source code or use the CLI as a reference for implementing similar functionality.