@Marvin why some tasks in MAP are not running in parallel?

In Prefect 2.0, tasks in a mapped flow are generally expected to run in parallel. However, there could be several reasons why some tasks within a map operation are not running in parallel: 1. Executor Configuration: If you are using an executor that does not support parallelism or is misconfigured, it might not run tasks in parallel. For example, the

LocalDaskExecutor

can be configured for threading or multiprocessing, and settings like the number of worker threads can limit parallelism. 2. Upstream Dependencies: Tasks within a map may have upstream dependencies that prevent them from running simultaneously. If a task depends on the output of another, it will only run once its dependencies are met. 3. System Limitations: System resources such as CPU, memory, or I/O can also limit parallel execution. If the tasks are resource-intensive, the system might not be able to execute many tasks in parallel. Additionally, if many tasks are trying to access the same resource (like a database), it could serially queue the tasks to avoid conflicts or overloading the resource. 4. Task Configuration: The way tasks are constructed and the flow of data between them can also influence parallel execution. If tasks are not truly independent or designed for concurrency, there might be implicit serialization. 5. Executor Implementation in Prefect 2.0: Depending on the executor used in Prefect 2.0, tasks might run on a single thread asynchronously, utilize multi-threading, or leverage multi-processing. Understanding the chosen executor's behavior is important to ensure that tasks are set up to run as intended. If you're experiencing unexpected serial execution of mapped tasks, it would be advisable to review their dependencies, resource requirements, and the configuration of the executor being used. Adjustments to the executor settings or task design might be needed to achieve the desired parallelism. It's also possible to file a discussion or issue in the Prefect community forums or GitHub repository to seek further assistance.

do you have concurrency limits? or are you using the SequenetialTaskRunner?