[jira] [Created] (CALCITE-1787) thetaSketch Support for Druid Adapter

["Zain Humayun (JIRA)" <ji...@apache.org>]

Zain Humayun created CALCITE-1787:
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             Summary: thetaSketch Support for Druid Adapter
                 Key: CALCITE-1787
                 URL: https://issues.apache.org/jira/browse/CALCITE-1787
             Project: Calcite
          Issue Type: New Feature
          Components: druid
    Affects Versions: 1.12.0
            Reporter: Zain Humayun
            Assignee: Julian Hyde
            Priority: Minor
             Fix For: 1.12.0


Currently, the Druid adapter does not support the [thetaSketch|http://druid.io/docs/latest/development/extensions-core/datasketches-aggregators.html] aggregate type, which is used to measure the cardinality of a column quickly. Many Druid instances support theta sketches, so I think it would be a nice feature to have.


I've been looking at the Druid adapter, and propose we add a new DruidType called {{thetaSketch}} and then add logic in the {{getJsonAggregation}} method in class {{DruidQuery}} to generate the {{thetaSketch}} aggregate. This will require accessing information about the columns (what data type they are) so that the thetaSketch aggregate is only produced if the column's type is {{thetaSketch}}. 


Also, I've noticed that a {{hyperUnique}} DruidType is currently defined, but a {{hyperUnique}} aggregate is never produced. Since both are approximate aggregators, I could also couple in the logic for {{hyperUnique}}.


I'd love to hear your thoughts on my approach, and any suggestions you have for this feature.



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