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https://issues.apache.org/jira/browse/FLINK-20059?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jark Wu closed FLINK-20059.
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Resolution: Fixed
> Outdated SQL docs on aggregate functions' merge
> -----------------------------------------------
>
> Key: FLINK-20059
> URL: https://issues.apache.org/jira/browse/FLINK-20059
> Project: Flink
> Issue Type: Bug
> Components: Documentation, Table SQL / API
> Affects Versions: 1.12.0, 1.11.2
> Reporter: Nico Kruber
> Assignee: Jark Wu
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.12.0
>
>
> In the java docs as well as the user docs, the {{merge}} method of an
> aggregation UDF is described as optional, e.g.
> {quote}Merges a group of accumulator instances into one accumulator instance.
> This function must be implemented for data stream session window grouping
> aggregates and data set grouping aggregates.{quote}
> However, it seems that nowadays this method is required in more cases (I
> stumbled on this for a HOP window in streaming):
> {code}
> StreamExecGlobalGroupAggregate.scala
> .needMerge(mergedAccOffset, mergedAccOnHeap, mergedAccExternalTypes)
> StreamExecGroupWindowAggregateBase.scala
> generator.needMerge(mergedAccOffset = 0, mergedAccOnHeap = false)
> StreamExecIncrementalGroupAggregate.scala
> .needMerge(mergedAccOffset, mergedAccOnHeap = true,
> mergedAccExternalTypes)
> StreamExecLocalGroupAggregate.scala
> .needMerge(mergedAccOffset = 0, mergedAccOnHeap = true)
> {code}
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