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https://issues.apache.org/jira/browse/SPARK-32698?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Manu Zhang resolved SPARK-32698.
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Resolution: Won't Do
> Do not fall back to default parallelism if the minimum number of coalesced
> partitions is not set in AQE
> -------------------------------------------------------------------------------------------------------
>
> Key: SPARK-32698
> URL: https://issues.apache.org/jira/browse/SPARK-32698
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Manu Zhang
> Priority: Minor
>
> Currently in AQE when coalescing shuffling partitions,
> {quote}We fall back to Spark default parallelism if the minimum number of
> coalesced partitions is not set, so to avoid perf regressions compared to no
> coalescing.
> {quote}
> From our experience, this has resulted in a lot of uncertainty of the number
> of tasks after coalescing especially with dynamic allocation, and also lead
> to many small output files. It's complex and hard to reason about.
> Hence, I'm proposing not falling back to the default parallelism but
> coalescing towards the target size when the minimum number of coalesced
> partitions is not set.
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