@Marvin prefect 2.x is ignoring some task runs, what could cause that?

There are several potential causes for Prefect 2.x task runs being ignored: 1. Concurrency and Task Runners: Prefect uses different task runners for executing tasks, such as

ConcurrentTaskRunner

and

SequentialTaskRunner

. If tasks are not running as expected, it might be due to the configuration of these runners. Ensure that the runner you are using is appropriate for your task's execution requirements. More information can be found in the Prefect Task Runners documentation. 2. Async Function Calls: If tasks involve asynchronous functions, ensure they are properly awaited. An example from GitHub issues indicates tasks might be ignored if async functions are not awaited correctly, which could lead to completed flow runs with no task executions. See GitHub Issue #14532. 3. Resource Constraints: If the execution environment is constrained, such as memory or CPU limitations, tasks might be skipped or ignored. This is particularly relevant if using distributed task runners like Dask or Ray. 4. Database Transaction Issues: For users using SQLite, known issues with transaction behavior might cause task states to be ignored due to race conditions. This can lead to unexpected behavior when updating task run states. See related PR #9594. 5. Configuration and Tags: Ensure that task configurations, such as tags and environment variables, are correctly set. Misconfiguration might lead to tasks being ignored. If none of these align with your situation, you might want to check your flow and task definitions for any specific conditions or configurations that could lead to tasks being skipped.

@Marvin my .map() tasks are not being submitted to run

If your

.map()

tasks are not being submitted to run in Prefect 2.x, consider the following potential issues and solutions: 1. Upstream Dependencies: Ensure that your mapped tasks have all upstream dependencies resolved. If a mapped task depends on results from other tasks, confirm those tasks complete successfully before the mapped tasks are triggered. You can manage this using the

wait_for

parameter. More details can be found in the Prefect documentation on upstream dependencies. 2. Ensure Tasks are Awaited: If your mapped tasks involve asynchronous operations, ensure they are properly awaited. Not doing so might lead to tasks being ignored or not executed. Ensure that you call

.result()

or

.wait()

on futures to ensure they resolve. 3. Logging and Errors: If your flow reports as completed but tasks are not executed, check for logs indicating issues such as "A future was garbage collected before it resolved." This can happen if the tasks are not properly awaited. See GitHub Issue #16373. 4. Configuration and Task Runner: Verify that the task runner is correctly set up and that tasks are being submitted to it. In some cases, tasks might not execute if they are not explicitly submitted. Ensure you're using

.submit()

or

.map()

methods appropriately. 5. Dask and Distributed Execution: If using Dask for distributed execution, ensure your Dask cluster is correctly configured and capable of handling the number of tasks you're trying to run. Bottlenecks in the cluster setup might prevent tasks from being scheduled. By addressing these areas, you should be able to diagnose why your

.map()

tasks are not being submitted. If issues persist, reviewing logs and error messages in detail will provide further insights.