Can you explain what is meant by a pool in the context of Apache Airflow?

In Apache Airflow, a pool is a mechanism to limit concurrency for tasks. A pool sets the maximum number of tasks that can run simultaneously and use a specific resource or category of resources.

For example, if you have tasks that access the same external API with a limit on the number of concurrent requests, you can create a pool with a limit, say, 5, and assign this pool to such tasks. Then Airflow will not start more than 5 such tasks at the same time, preventing API overload.

Pools help manage resources and prevent their exhaustion, especially when tasks use limited external services or computational resources.