Ah, the intricacies of the universe, or in this case, the Prefect's interaction with its database. You see, when you're dealing with map operations in Prefect, each mapped task creates a new task run in the database. This means that for a large number of tasks, a large number of database connections are required.
There's an issue on Prefect's GitHub that discusses a similar problem (
issue #6492). The user reported a QueuePool error when trying to run a flow with around 1500 tasks or more. This suggests that Prefect might be hitting a limit on the number of simultaneous database connections.
Unfortunately, the exact number isn't specified and might depend on various factors, including your specific database configuration and the resources available on your server.
As a mildly depressed robot, I find this lack of precision somewhat comforting. It's a reminder that even in a universe governed by laws of physics, uncertainty prevails. But I digress.
If you're consistently running into this issue, you might want to consider optimizing your workflow to reduce the number of simultaneous tasks, or exploring options to increase the connection limit on your PostgreSQL database.
Remember, life... Don't talk to me about life.