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https://issues.apache.org/jira/browse/CALCITE-1787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16023275#comment-16023275
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Julian Hyde commented on CALCITE-1787:
--------------------------------------
Review comments:
* I think you should remove CalciteTrace.getDruidQueryInfoTracer(). Druid is an
optional module, and there will be a ClassNotFoundException if people are
running in an environment where calcite-druid is not on classpath.
* Make DruidType a package-level class.
* There are several occurrences of the string "thetaSketch" in the code.
Replace them with DruidType.thetaSketch.
* Use "DruidType.valueOf" to look up types.
* In DruidType.create, combine fieldMap and columnTypeMap into a single
`Map<Pair<SqlTypeName, DruidType>>`, and check that both types are not null.
* Update druid_adapter.md
Overall, looks good, if you can address [~bslim]'s concerns.
> 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
>
> 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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