[jira] [Commented] (SPARK-32698) Do not fall back to default parallelism if the minimum number of coalesced partitions is not set in AQE

["Apache Spark (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-32698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17184009#comment-17184009 ] 

Apache Spark commented on SPARK-32698:
--------------------------------------

User 'manuzhang' has created a pull request for this issue:
https://github.com/apache/spark/pull/29540

> 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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