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Posted to issues@spark.apache.org by "Dongjoon Hyun (JIRA)" <ji...@apache.org> on 2019/03/04 23:42:00 UTC
[jira] [Resolved] (SPARK-26205) Optimize InSet expression for
bytes, shorts, ints, dates
[ https://issues.apache.org/jira/browse/SPARK-26205?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Dongjoon Hyun resolved SPARK-26205.
-----------------------------------
Resolution: Fixed
Assignee: Anton Okolnychyi
Fix Version/s: 3.0.0
This is resolved via https://github.com/apache/spark/pull/23171 .
> Optimize InSet expression for bytes, shorts, ints, dates
> --------------------------------------------------------
>
> Key: SPARK-26205
> URL: https://issues.apache.org/jira/browse/SPARK-26205
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Anton Okolnychyi
> Assignee: Anton Okolnychyi
> Priority: Major
> Fix For: 3.0.0
>
>
> {{In}} expressions are compiled into a sequence of if-else statements, which results in O\(n\) time complexity. {{InSet}} is an optimized version of {{In}}, which is supposed to improve the performance if the number of elements is big enough. However, {{InSet}} actually degrades the performance in many cases due to various reasons (benchmarks were created in SPARK-26203 and solutions to the boxing problem are discussed in SPARK-26204).
> The main idea of this JIRA is to use Java {{switch}} statements to significantly improve the performance of {{InSet}} expressions for bytes, shorts, ints, dates. All {{switch}} statements are compiled into {{tableswitch}} and {{lookupswitch}} bytecode instructions. We will have O\(1\) time complexity if our case values are compact and {{tableswitch}} can be used. Otherwise, {{lookupswitch}} will give us O\(log n\). Our local benchmarks show that this logic is more than two times faster even on 500+ elements than using primitive collections in {{InSet}} expressions. As Spark is using Scala {{HashSet}} right now, the performance gain will be is even bigger.
> See [here|https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-3.html#jvms-3.10] and [here|https://stackoverflow.com/questions/10287700/difference-between-jvms-lookupswitch-and-tableswitch] for more information.
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