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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