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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-25306) Avoid skewed filter trees to speed up `createFilter` in ORC
Date Wed, 05 Sep 2018 05:18:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-25306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16603926#comment-16603926
] 

Apache Spark commented on SPARK-25306:
--------------------------------------

User 'dongjoon-hyun' has created a pull request for this issue:
https://github.com/apache/spark/pull/22336

> Avoid skewed filter trees to speed up `createFilter` in ORC
> -----------------------------------------------------------
>
>                 Key: SPARK-25306
>                 URL: https://issues.apache.org/jira/browse/SPARK-25306
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 1.6.3, 2.0.2, 2.1.3, 2.2.2, 2.3.1, 2.4.0
>            Reporter: Dongjoon Hyun
>            Assignee: Dongjoon Hyun
>            Priority: Critical
>             Fix For: 2.4.0
>
>
> In both ORC data sources, createFilter function has exponential time complexity due to
its skewed filter tree generation. This PR aims to improve it by using new buildTree function.
> *REPRODUCE*
> {code}
> // Create and read 1 row table with 1000 columns
> sql("set spark.sql.orc.filterPushdown=true")
> val selectExpr = (1 to 1000).map(i => s"id c$i")
> spark.range(1).selectExpr(selectExpr: _*).write.mode("overwrite").orc("/tmp/orc")
> print(s"With 0 filters, ")
> spark.time(spark.read.orc("/tmp/orc").count)
> // Increase the number of filters
> (20 to 30).foreach { width =>
>   val whereExpr = (1 to width).map(i => s"c$i is not null").mkString(" and ")
>   print(s"With $width filters, ")
>   spark.time(spark.read.orc("/tmp/orc").where(whereExpr).count)
> }
> {code}
> *RESULT*
> {code}
> With 0 filters, Time taken: 653 ms                                              
> With 20 filters, Time taken: 962 ms
> With 21 filters, Time taken: 1282 ms
> With 22 filters, Time taken: 1982 ms
> With 23 filters, Time taken: 3855 ms
> With 24 filters, Time taken: 6719 ms
> With 25 filters, Time taken: 12669 ms
> With 26 filters, Time taken: 25032 ms
> With 27 filters, Time taken: 49585 ms
> With 28 filters, Time taken: 98980 ms    // over 1 min 38 seconds
> With 29 filters, Time taken: 198368 ms   // over 3 mins
> With 30 filters, Time taken: 393744 ms   // over 6 mins
> {code}



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