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https://issues.apache.org/jira/browse/SPARK-34253?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17272495#comment-17272495
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Apache Spark commented on SPARK-34253:
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User 'c21' has created a pull request for this issue:
https://github.com/apache/spark/pull/31353
> Object hash aggregate should not fallback if no more input rows
> ---------------------------------------------------------------
>
> Key: SPARK-34253
> URL: https://issues.apache.org/jira/browse/SPARK-34253
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: Cheng Su
> Priority: Trivial
>
> Object hash aggregate will fallback to sort-based aggregation based on number
> of keys seen so far [0]. The default config threshold is 128
> (spark.sql.objectHashAggregate.sortBased.fallbackThreshold in [1]). There's
> an edge case we can do better, where we do not fallback if there's no more
> input rows. Suppose the task only has 128 group-by keys in hash ma, we don't
> need to fallback in this case, and we can save the extra sort.
>
> [0]:
> [https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/ObjectAggregationIterator.scala#L161]
>
> [1]:
> [https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala#L1615]
>
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