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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2019/03/27 03:44:48 UTC
[GitHub] [spark] cloud-fan commented on issue #24215: [SPARK-27229][SQL]
GroupBy Placement in Intersect Distinct
cloud-fan commented on issue #24215: [SPARK-27229][SQL] GroupBy Placement in Intersect Distinct
URL: https://github.com/apache/spark/pull/24215#issuecomment-476959548
I'm afraid this may cause big regression, as aggregate is expensive and here we do it twice.
Aggregate needs to build a hash map, which may spill to disk if data is large. If the aggregate doesn't help with data reduction, we hit regression.
Unless there is a proposal to resolve the regression, I think we shouldn't merge it.
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