@Marvin what exactly is the difference between polling frequency and prefetch frequency?

In Prefect, polling frequency and prefetch frequency have distinct roles related to how tasks and infrastructure are managed. 1. Polling Frequency: This relates to how often Prefect workers check for new tasks to execute. By default, workers poll for work every 15 seconds, but you can adjust this frequency using the

PREFECT_WORKER_QUERY_SECONDS

setting. It's like checking the fridge for snacks every few minutes to see if something new magically appeared! For more details, you can check here for Prefect 3.x and here for Prefect 2.x. 2. Prefetch Frequency: Prefetching is related to the timing of flow runs. By default, Prefect workers submit flow runs 10 seconds before they're scheduled to start. This allows time for the necessary infrastructure to spin up so the task can start on time. If your infrastructure needs more time, you can increase this prefetch time with the

PREFECT_WORKER_PREFETCH_SECONDS

setting. Think of it as setting your coffee machine to brew just before you wake up, so your coffee is perfectly timed! For more info, see Prefect 3.x here and Prefect 2.x here. Hopefully, that clears things up, and you'll never confuse polling with prefetching again—unless, of course, you're like me and enjoy mixing things up for fun!

@Marvin how would I know if I need more prefetch time?

Determining if you need more prefetch time generally comes down to observing the behavior of your flow runs and the infrastructure they depend on. Here are a few indicators that you might need to adjust your prefetch time: 1. Delayed Start: If your flow runs consistently start later than their scheduled times due to the infrastructure not being ready, it's a clear sign that you might need to increase the prefetch time. The goal is to have the infrastructure fully spun up by the scheduled start time. 2. Infrastructure Spin-Up Time: Consider the time it takes for your infrastructure to become operational. If the default 10 seconds is insufficient for your infrastructure to initialize and be ready, then you should increase the prefetch time to a value that matches your infrastructure's spin-up requirements. 3. Log Observations: If you notice in your logs that the tasks are waiting for infrastructure readiness after their scheduled start, it's another clue. Adjust the value of the

PREFECT_WORKER_PREFETCH_SECONDS

or

--prefetch-seconds

option to account for this delay. More detailed guidance can be found in the Prefect documentation for Prefect 3.x here and for Prefect 2.x here. Remember, while increasing prefetch time, ensure that it is only as long as necessary to keep your flows starting on time, as this can affect resource utilization.

@Marvin how can I make it startup faster? I don’t really care about “scheduling” into the future, I want the job to start as soon as I emit it

To start a task immediately in Prefect, you have a couple of options, depending on whether you're using Prefect 2.x or 3.x. 1. Immediate Execution in Prefect 2.x: - When you run a flow directly from a script, tasks are executed as soon as they're called. This is ideal for triggering tasks without future scheduling. For example, executing a script would look something like

python my_flow_script.py

, and Prefect will handle the task execution immediately. You can see more about this in the Prefect 2.x quickstart guide. 2. Immediate Execution in Prefect 3.x: - Similar to Prefect 2.x, Prefect 3.x allows for immediate task execution by running tasks without defining a schedule for future runs. Prefect 3.x workflows can be triggered to start right away, bypassing the scheduling mechanism entirely. More details can be found in the Prefect 3.x documentation. By executing your tasks in this direct manner, you ensure that they start as soon as possible after you emit the command, bypassing scheduling into the future. This approach is like getting your pizza delivered immediately instead of scheduling it for dinner tomorrow!