kaxil commented on code in PR #64571:
URL: https://github.com/apache/airflow/pull/64571#discussion_r3317834471


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airflow-core/newsfragments/64571.significant.rst:
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@@ -29,8 +29,33 @@ an hourly partition).
 
 Mappers can be set globally on a ``PartitionedAssetTimetable`` or overridden 
per upstream asset via ``partition_mapper_config``.
 
+**Rollup (one downstream run per window of upstream partitions)**:
+
+- ``RollupMapper`` — wraps a ``upstream_mapper`` (which normalises the 
upstream key to the

Review Comment:
   Newsfragment looks good. But the narrative doc side feels thin -- 
`airflow-core/docs/authoring-and-scheduling/assets.rst` - "Asset partitions" 
(lines 496-630) covers the non-rollup mappers but doesn't reach the rollup 
case. No subsection showing how to compose 
`RollupMapper(upstream_mapper=StartOfDayMapper(), window=DayWindow())` onto a 
`PartitionedAssetTimetable`, no "hourly -> daily summary" worked example, and 
the DST mitigation lives in the newsfragment but not anywhere a user is likely 
to read while building this.
   
   Autoapi entries cover the reference but they won't help someone landing on 
assets.rst trying to figure out if the feature exists. Either drop a section in 
here before the 3.3 freeze or open a follow-up doc PR -- not necessarily 
blocking but probably wants to ship in the same release.
   
   (Also, the existing partitions section is at 
[`authoring-and-scheduling/assets.rst#asset-partitions`](https://github.com/apache/airflow/blob/main/airflow-core/docs/authoring-and-scheduling/assets.rst)
 for context.)



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