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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2021/04/13 13:39:28 UTC

[GitHub] [spark] cloud-fan commented on pull request #32057: [SPARK-34961][SQL] Migrate First function from DeclarativeAggregate to TypedImperativeAggregate to improve performance

cloud-fan commented on pull request #32057:
URL: https://github.com/apache/spark/pull/32057#issuecomment-818743773


   AFAIK it's for historical reasons. `ObjectHashAggregateExec` was created to speed up certain aggregate functions that use java objects as states, and we made a very conservative trigger condition for `ObjectHashAggregateExec`.
   
   In general, I agree with what @tanelk said, but there is one issue that: `ObjectHashAggregateExec` is bad at memory estimation and may easily OOM. `SortAggregateExec` is more robust (but slower).


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