[GitHub] [arrow-datafusion] Dandandan commented on issue #5547: Improve the performance of COUNT DISTINCT queries for high cardinality groups

["Dandandan (via GitHub)" <gi...@apache.org>]

Dandandan commented on issue #5547:
URL: https://github.com/apache/arrow-datafusion/issues/5547#issuecomment-1463855313

   Another option which I suggested earlier would be similar to dictionary array builder (https://docs.rs/arrow-array/34.0.0/src/arrow_array/builder/primitive_dictionary_builder.rs.html#82) - without maintaining the actual values.
   
   This would probably be a bit faster than (though compared to `HashSet<ScalarValue>` both probably are far more efficient) than using the row format (as we don't need to do the conversion plus hashing on primitive values can be a bit faster and specialized). For `COUNT DISTINCT` we only need to support single columns. 


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