godfreyhe opened a new pull request #10271: [FLINK-14874] [table-planner-blink] add local aggregate to solve data skew for ROLLUP/CUBE case URL: https://github.com/apache/flink/pull/10271 ## What is the purpose of the change * use case: Many tpc-ds queries have rollup keyword, which will be translated to multiple groups. for example: group by rollup (channel, id) is equivalent group by (channel, id) + group by (channel) + group by (). All data on empty group will be shuffled to a single node, It is a typical data skew case. If there is a local aggregate, the data size shuffled to the single node will be greatly reduced. However, currently the cost mode can't estimate the local aggregate's cost, and the plan with local aggregate may be chose even the query has rollup keyword. add a rule based phase (after physical phase) to enforce local aggregate if it's input has empty group. * ## Brief change log - *Add EnforceLocalHashAggRule and EnforceLocalSortAggRule* ## Verifying this change This change added tests and can be verified as follows: - *Added EnforceLocalHashAggRuleTest and EnforceLocalSortAggRuleTest that validates the result of the rules* ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): (yes / **no)** - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (yes / **no)** - The serializers: (yes / **no** / don't know) - The runtime per-record code paths (performance sensitive): (yes / **no** / don't know) - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / **no** / don't know) - The S3 file system connector: (yes / **no** / don't know) ## Documentation - Does this pull request introduce a new feature? (yes / **no)** - If yes, how is the feature documented? (not applicable / docs / JavaDocs / **not documented**)
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