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https://issues.apache.org/jira/browse/FLINK-6394?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Robert Metzger updated FLINK-6394:
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Component/s: DataSet API
> GroupCombine reuses instances even though object reuse is disabled
> ------------------------------------------------------------------
>
> Key: FLINK-6394
> URL: https://issues.apache.org/jira/browse/FLINK-6394
> Project: Flink
> Issue Type: Bug
> Components: DataSet API
> Affects Versions: 1.2.0
> Reporter: Jaromir Vanek
> Assignee: Kurt Young
> Priority: Critical
>
> I am using group combiner in DataSet API with disabled object reuse.
> In code it may be expressed as follows:
> {code:java}
> tuples.groupBy(1)
> .combineGroup((it, collector) -> {
> // store first item for future use
> Pojo stored = it.next();
> while (it.hasNext()) {
> ....
> }
> })
> {code}
> It seems even the object reuse feature is disabled, my instance is actually
> replaced when {{.next()}} is called on the iterator. It leads to very
> confusing and wrong results.
> I checked the Flink codebase and it seems {{CombiningUnilateralSortMerger}}
> is actually reusing object instances even though object reuse is explicitly
> disabled.
> In spilling phase user's combiner is called with instance of
> {{CombineValueIterator}} that actually reuses instances without any warning.
> See
> https://github.com/apache/flink/blob/d7b59d761601baba6765bb4fc407bcd9fd6a9387/flink-runtime/src/main/java/org/apache/flink/runtime/operators/sort/CombiningUnilateralSortMerger.java#L550
> When I disable combiner and use {{groupReduce}} only with the same reduce
> function, results are fine.
> Please let me know if you can confirm this as a bug. From my point of view
> it's highly critical as I am getting unpredictable results.
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