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https://issues.apache.org/jira/browse/CALCITE-1787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16051261#comment-16051261
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Zain Humayun commented on CALCITE-1787:
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wouldn't the "metricName" field need to be there to tell calcite which sketch
to refer to? For example,
{code:none}
{
"name" : "user",
"type" : "hyperUnique",
"meticName" : "user_unique"
}
{code}
"user_unique" would not be exposed to the user, and an error would be given if
they tried to use it in a query. But, when "user" is used correctly in a
statement, say, count(distinct user), then the druid adapter will know to use
the "user_unique" column under the hood. In this case, "user" is not actually a
column in Druid anywhere, and "user_unique" is defined as a metric in the Druid
ingestion spec. Also, is there a specific existing exception the adapter should
throw?
> 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: Zain Humayun
> 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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