[GitHub] [druid] cloventt commented on a diff in pull request #13088: Add a note to the documentation about pre-built HLLSketches

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

cloventt commented on code in PR #13088:
URL: https://github.com/apache/druid/pull/13088#discussion_r973784680


##########
docs/development/extensions-core/datasketches-hll.md:
##########
@@ -89,6 +94,11 @@ druid.extensions.loadList=["druid-datasketches"]
  }
 ```
 
+The `HLLSketchMerge` aggregator can be used to ingest pre-generated sketches from an input dataset. For example, an
+earlier batch processing job can be used to generate the sketches before the data is sent to Druid. To support this
+behaviour, the sketches in the input dataset must be serialised to base64-encoded bytes. Then, in the native ingestion
+`MetricsSpec` the `HLLSketchMerge` must be specified for the input column as shown above.
+

Review Comment:
   I'm not sure on the usefulness of an example - the code blob to be added to the `MetricsSpec` is already included directly above this paragraph.



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