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https://issues.apache.org/jira/browse/FLINK-7204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16089678#comment-16089678
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ASF GitHub Bot commented on FLINK-7204:
---------------------------------------
Github user fhueske commented on the issue:
https://github.com/apache/flink/pull/4350
Hi @greghogan, I think this is definitely a valuable improvement.
However, I looked at the plan of a query with a `ReduceFunction` with
`CombineHint.None` and found that it still has a combine node:
```
[IN] -FWD-> [COMBINE(SORTED_REDUCE)] -HASH-> [REDUCE(SORTED_REDUCE)] ->
[OUT]
```
I think we should
1. set `combinerStrategy` to `DriverStrategy.NONE` in `ReduceNode` for
`CombineHint.NONE`.
2. change `ReduceProperties.instantiate()` with a check for
`combinerStrategy == NONE` and not add a node for the combiner in that case.
3. add a test in `ReduceCompilationTest` similar to
`testGroupedReduceWithHint()` to check that the resulting plan has no combine
node.
Best, Fabian
> CombineHint.NONE
> ----------------
>
> Key: FLINK-7204
> URL: https://issues.apache.org/jira/browse/FLINK-7204
> Project: Flink
> Issue Type: New Feature
> Components: Core
> Affects Versions: 1.4.0
> Reporter: Greg Hogan
> Assignee: Greg Hogan
> Priority: Minor
>
> FLINK-3477 added a hash-combine preceding the reducer configured with
> {{CombineHint.HASH}} or {{CombineHint.SORT}} (default). In some cases it may
> be useful to disable the combiner in {{ReduceNode}} by specifying a new
> {{CombineHint.NONE}} value.
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