capistrant commented on code in PR #19213:
URL: https://github.com/apache/druid/pull/19213#discussion_r2997750333


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docs/data-management/cascading-reindexing.md:
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@@ -0,0 +1,412 @@
+---
+id: cascading-reindexing
+title: "Cascading reindexing"
+---
+
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+  ~ under the License.
+  -->
+
+:::info
+Cascading reindexing is an experimental feature introduced in Druid 37. Its 
API may change in future releases. This feature is only for automatic 
compaction using [compaction 
supervisors](automatic-compaction.md#auto-compaction-using-compaction-supervisors)
 with the [MSQ compaction 
engine](automatic-compaction.md#use-msq-for-auto-compaction).
+:::
+
+Cascading reindexing is a compaction supervisor template that lets you define 
age-based rules to automatically apply different compaction configurations as 
data ages. Instead of a single flat compaction configuration for an entire 
datasource, you define rules that say "for data older than X, apply 
configuration Y." Reindexing is a more general term than compaction. Reindexing 
not only can merge segments with the same schema and partitioning, but also can 
change the segment schema, partitioning, and encoding. Cascading reindexing 
gives you fine-grained control over how your data evolves over time.
+
+For example, you might want to:
+- Keep recent data in hourly segments, but coarsen to daily segments after 90 
days to help reduce segment count and storage footprint.
+- Delete some unwanted rows from data older than 30 days.
+- Change compression settings for older data.
+- Roll up older data to a coarser query granularity for data .

Review Comment:
   ```suggestion
   - Roll up older data to a coarser query granularity
   ```



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