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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2018/11/28 19:09:00 UTC
[jira] [Commented] (SPARK-26205) Optimize In expression for bytes,
shorts, ints
[ https://issues.apache.org/jira/browse/SPARK-26205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16702293#comment-16702293 ]
Apache Spark commented on SPARK-26205:
--------------------------------------
User 'aokolnychyi' has created a pull request for this issue:
https://github.com/apache/spark/pull/23171
> Optimize In expression for bytes, shorts, ints
> ----------------------------------------------
>
> 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
> Priority: Major
>
> Currently, {{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 will be available in SPARK-26203 and solutions are discussed in SPARK-26204).
> The main idea of this JIRA is to make use of {{tableswitch}} and {{lookupswitch}} bytecode instructions. In short, we can improve our time complexity from O\(n\) to O\(1\) or at least O\(log n\) by using Java {{switch}} statements. We will have O\(1\) time complexity if our case values are compact and {{tableswitch}} can be used. Otherwise, {{lookupswitch}} will give us O\(log n\).
> An important benefit of the proposed approach is that we do not have to pay an extra cost for autoboxing as in case of {{InSet}}. As a consequence, we can substantially outperform {{InSet}} even on 250+ elements.
> 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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