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| |
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| |
| .. _concepts:priority-weight: |
| |
| 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 |
| :class:`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 :ref:`concepts:pool`. |