Compare taskgroup and subdag

docs/apache-airflow/concepts/dags.rst

@@ -582,13 +582,15 @@ Note that SubDAG operators should contain a factory method that returns a DAG ob
     :start-after: [START subdag]
     :end-before: [END subdag]
 
+
 This SubDAG can then be referenced in your main DAG file:
 
 .. exampleinclude:: /../../airflow/example_dags/example_subdag_operator.py
     :language: python
     :start-after: [START example_subdag_operator]
     :end-before: [END example_subdag_operator]
 
+
 You can zoom into a :class:`~airflow.operators.subdag.SubDagOperator` from the graph view of the main DAG to show the tasks contained within the SubDAG:
 
 .. image:: /img/subdag_zoom.png
@@ -609,6 +611,37 @@ Note that :doc:`pools` are *not honored* by :class:`~airflow.operators.subdag.Su
 resources could be consumed by SubdagOperators beyond any limits you may have set.
 
 
+TaskGroups vs SubDAGs
+----------------------
+
+SubDAGs, while serving a similar purpose as TaskGroups, introduces both performance and functional issues due to its implementation.
+
+* The SubDagOperator starts a BackfillJob, which ignores existing parallelism configurations potentially oversubscribing the worker environment.
+* SubDAGs have their own DAG attributes. When the SubDAG DAG attributes are inconsistent with its parent DAG, unexpected behavior can occur.
+* Unable to see the "full" DAG in one view as SubDAGs exists as a full fledged DAG.
+* SubDAGs introduces all sorts of edge cases and caveats. This can disrupt user experience and expectation.
+
+TaskGroups, on the other hand, is a better option given that it is purely a UI grouping concept. All tasks within the TaskGroup still behave as any other tasks outside of the TaskGroup.
+
+You can see the core differences between these two constructs.
+
++--------------------------------------------------------+--------------------------------------------------------+
+| TaskGroup                                              | SubDAG                                                 |
++========================================================+========================================================+
+| Repeating patterns as part of the same DAG             |  Repeating patterns as a separate DAG                  |
++--------------------------------------------------------+--------------------------------------------------------+
+| One set of views and statistics for the DAG            |  Separate set of views and statistics between parent   |
+|                                                        |  and child DAGs                                        |
++--------------------------------------------------------+--------------------------------------------------------+
+| One set of DAG configuration                           |  Several sets of DAG configurations                    |
++--------------------------------------------------------+--------------------------------------------------------+
+| Honours parallelism configurations through existing    |  Does not honour parallelism configurations due to     |
+| SchedulerJob                                           |  newly spawned BackfillJob                             |
++--------------------------------------------------------+--------------------------------------------------------+
+| Simple construct declaration with context manager      |  Complex DAG factory with naming restrictions          |
++--------------------------------------------------------+--------------------------------------------------------+
+
+
 Packaging DAGs
 --------------