Priority Weights

priority_weight defines priorities in the executor queue. The default priority_weight is 1, and can be bumped to any integer. Moreover, each task has a true priority_weight that is calculated based on its weight_rule which defines weighting method used for the effective total priority weight of the task.

By default, Airflow’s weighting method is downstream. You can find other weighting methods in airflow.utils.WeightRule.

There are three weighting methods.

• downstream

  The effective weight of the task is the aggregate sum of all downstream descendants. As a result, upstream tasks will have higher weight and will be scheduled more aggressively when using positive weight values. This is useful when you have multiple DAG run instances and desire to have all upstream tasks to complete for all runs before each DAG can continue processing downstream tasks.

• upstream

  The effective weight is the aggregate sum of all upstream ancestors. This is the opposite where downstream tasks have higher weight and will be scheduled more aggressively when using positive weight values. This is useful when you have multiple DAG run instances and prefer to have each DAG complete before starting upstream tasks of other DAG runs.

• absolute

  The effective weight is the exact priority_weight specified without additional weighting. You may want to do this when you know exactly what priority weight each task should have. Additionally, when set to absolute, there is bonus effect of significantly speeding up the task creation process as for very large DAGs

The priority_weight parameter can be used in conjunction with Pools.