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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