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https://issues.apache.org/jira/browse/FLINK-6888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16045992#comment-16045992
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Jark Wu commented on FLINK-6888:
--------------------------------
Hi [~sunjincheng121], you are right that all the build-in AGGs work good but
user-defined aggs with Scala accumulator might not as mentioned in FLINK-5957
by Fabian. The {{getAccumulatorType()}} contract method can solve this issue
but it's trivial to implement this method for every Scala accumulator.
So I suggest to extract ACC type information when {{registerFunction}} using
Scala implicit parameters.
> Can not determine TypeInformation of ACC type of AggregateFunction when ACC
> is a Scala case/tuple class
> -------------------------------------------------------------------------------------------------------
>
> Key: FLINK-6888
> URL: https://issues.apache.org/jira/browse/FLINK-6888
> Project: Flink
> Issue Type: Bug
> Components: Table API & SQL
> Reporter: Jark Wu
> Assignee: Jark Wu
> Fix For: 1.4.0
>
>
> Currently the {{ACC}} TypeInformation of
> {{org.apache.flink.table.functions.AggregateFunction[T, ACC]}} is extracted
> using {{TypeInformation.of(Class)}}. When {{ACC}} is a Scala case class or
> tuple class, the TypeInformation will fall back to {{GenericType}} which
> result in bad performance when state de/serialization.
> I suggest to extract the ACC TypeInformation when called
> {{TableEnvironment.registerFunction()}}.
> Here is an example:
> {code}
> case class Accumulator(sum: Long, count: Long)
> class MyAgg extends AggregateFunction[Long, Accumulator] {
> //Overloaded accumulate method
> def accumulate(acc: Accumulator, value: Long): Unit = {
> }
> override def createAccumulator(): Accumulator = Accumulator(0, 0)
> override def getValue(accumulator: Accumulator): Long = 1
> }
> {code}
> The {{Accumulator}} will be recognized as {{GenericType<Accumulator>}}.
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