abhishekagarwal87 commented on a change in pull request #11482:
URL: https://github.com/apache/druid/pull/11482#discussion_r674681552
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File path: docs/development/extensions-core/datasketches-hll.md
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@@ -45,6 +59,25 @@ druid.extensions.loadList=["druid-datasketches"]
}
```
+> It is very common to use `HLLSketchBuild` in combination with
[rollup](../../ingestion/index.html#rollup) to create a
[metric](../../ingestion/index.html#metricsspec) on high-cardinality columns.
In this example, a metric called `userid_hll` is included in the `metricsSpec`.
This will perform a HLL sketch on the `userid` field at ingestion time,
allowing for highly-performant approximate `COUNT DISTINCT` query operations
_and_ improving roll-up ratios when `userid` is then left out of the
`dimensionsSpec`.
Review comment:
###
```suggestion
> It is very common to use `HLLSketchBuild` in combination with
[rollup](../../ingestion/index.html#rollup) to create a
[metric](../../ingestion/index.html#metricsspec) on high-cardinality columns.
In this example, a metric called `userid_hll` is included in the `metricsSpec`.
This will perform a HLL sketch on the `userid` field at ingestion time,
allowing for highly-performant approximate `COUNT DISTINCT` query operations
and improving roll-up ratios when `userid` is then left out of the
`dimensionsSpec`.
```
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