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From "Sital Kedia (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23310) Perf regression introduced by SPARK-21113
Date Sat, 03 Feb 2018 00:10:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16351097#comment-16351097
] 

Sital Kedia commented on SPARK-23310:
-------------------------------------

https://github.com/apache/spark/pull/20492

> 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
>            Priority: Blocker
>
> 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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