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https://issues.apache.org/jira/browse/FLINK-4855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15589378#comment-15589378
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Greg Hogan commented on FLINK-4855:
-----------------------------------
Hi and thanks for submitting a ticket for this idea! Has this been discussed on
the dev mailing list (if yes, please add a link)? It looks like a major
addition to the DataStream API and should be fully vetted before starting.
> Add partitionedKeyBy to DataStream
> ----------------------------------
>
> Key: FLINK-4855
> URL: https://issues.apache.org/jira/browse/FLINK-4855
> Project: Flink
> Issue Type: Improvement
> Components: DataStream API
> Reporter: Xiaowei Jiang
> Assignee: MaGuowei
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> After we do any interesting operations (e.g. reduce) on KeyedStream, the
> result becomes DataStream. In a lot of cases, the output still has the same
> or compatible keys with the KeyedStream (logically). But to do further
> operations on these keys, we are forced to use keyby again. This works
> semantically, but is costly in two aspects. First, it destroys the
> possibility of chaining, which is one of the most important optimization
> technique. Second, keyby will greatly expand the connected components of
> tasks, which has implications in failover optimization.
> To address this shortcoming, we propose a new operator partitionedKeyBy.
> DataStream {
> public <K> KeyedStream<T, K> partitionedKeyBy(KeySelector<T, K> key)
> }
> Semantically, DataStream.partitionedKeyBy(key) is equivalent to
> DataStream.keyBy(partitionedKey) where partitionedKey is key plus the taskid
> as an extra field. This guarantees that records from different tasks will
> never produce the same keys.
> With this, it's possible to do
> ds.keyBy(key1).reduce(func1)
> .partitionedKeyBy(key1).reduce(func2)
> .partitionedKeyBy(key2).reduce(func3);
> Most importantly, in certain cases, we will be able to chains these into a
> single vertex.
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