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https://issues.apache.org/jira/browse/SPARK-23310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16359429#comment-16359429
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Kazuaki Ishizaki commented on SPARK-23310:
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got it, thanks
> Perf regression introduced by SPARK-21113
> -----------------------------------------
>
> Key: SPARK-23310
> URL: https://issues.apache.org/jira/browse/SPARK-23310
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.3.0
> Reporter: Yin Huai
> Assignee: Sital Kedia
> Priority: Blocker
> Fix For: 2.3.0
>
>
> While running all TPC-DS queries with SF set to 1000, we noticed that Q95
> (https://github.com/databricks/spark-sql-perf/blob/master/src/main/resources/tpcds_2_4/q95.sql)
> has noticeable regression (11%). After looking into it, we found that the
> regression was introduced by SPARK-21113. Specially, ReadAheadInputStream
> gets lock congestion. After setting
> spark.unsafe.sorter.spill.read.ahead.enabled set to false, the regression
> disappear and the overall performance of all TPC-DS queries has improved.
>
> I am proposing that we set spark.unsafe.sorter.spill.read.ahead.enabled to
> false by default for Spark 2.3 and re-enable it after addressing the lock
> congestion issue.
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