[GitHub] [airflow] eladkal commented on a diff in pull request #27250: Add note about pushing the lazy XCom proxy to XCom

[GitBox <gi...@apache.org>]

eladkal commented on code in PR #27250:
URL: https://github.com/apache/airflow/pull/27250#discussion_r1005696070


##########
docs/apache-airflow/concepts/dynamic-task-mapping.rst:
##########
@@ -72,6 +72,17 @@ The grid view also provides visibility into your mapped tasks in the details pan
 
     You can use normal sequence syntax on this object (e.g. ``values[0]``), or iterate through it normally with a ``for`` loop. ``list(values)`` will give you a "real" ``list``, but please be aware of the potential performance implications if the list is large.
 
+    Note that the same also applies to when you push this proxy object into XCom. This, for example, would not
+    work with the default XCom backend:
+
+    .. code-block:: python
+
+        @task
+        def forward_values(values):
+            return values  # This is a lazy proxy and can't be pushed!
+
+    You need to explicitly call ``list(values)`` instead, and accept the performance implications.

Review Comment:
   This invites the question of what implications and how can you tell if it's dramatic or not.
   If this is something we discourage under any circumstances I would use a stronger language



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