[jira] [Created] (FLINK-3479) Add hash-based strategy for CombineFunction

[Shang Yuanchun (Jira)]

Fabian Hueske created FLINK-3479:
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             Summary: Add hash-based strategy for CombineFunction
                 Key: FLINK-3479
                 URL: https://issues.apache.org/jira/browse/FLINK-3479
             Project: Flink
          Issue Type: Sub-task
          Components: Local Runtime
            Reporter: Fabian Hueske


This issue is similar to FLINK-3477 but adds a hash-based strategy for {{CombineFunction}} instead of {{ReduceFunction}}.

The interface of {{CombineFunction}} differs from {{ReduceFunction}} by providing an {{Iterable<T>}} instead of two {{T}} values. Hence, if the {{Iterable<T>}} provides two values, we can do the same as with a {{ReduceFunction}}.

At the moment, {{CombineFunction}} is wrapped in a {{GroupCombineFunction}} and hence executed using the {{GroupReduceCombineDriver}}.
We should add dedicated two dedicated drivers: {{CombineDriver}} and {{ChainedCombineDriver}} and two driver strategies: {{HASH_COMBINE}} and {{SORT_COMBINE}}.

If FLINK-3477 is resolved, we can reuse the hash-table.



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