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From "Reynold Xin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23964) why does Spillable wait for 32 elements?
Date Wed, 11 Apr 2018 19:37:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16434460#comment-16434460
] 

Reynold Xin commented on SPARK-23964:
-------------------------------------

Was it trying to reduce overhead?

 

> why does Spillable wait for 32 elements?
> ----------------------------------------
>
>                 Key: SPARK-23964
>                 URL: https://issues.apache.org/jira/browse/SPARK-23964
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 2.2.1
>            Reporter: Thomas Graves
>            Priority: Major
>
> The spillable class has a check in maybeSpill as to when it tries to acquire more memory
and determine if it should spill:
> if (elementsRead % 32 == 0 && currentMemory >= myMemoryThreshold) {
> Before it looks to see if it should spill.  
> [https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/util/collection/Spillable.scala#L83]
> I'm wondering why it has the elementsRead %32  in it?  If I have a small number of
elements that are huge this can easily cause OOM before we actually spill.  
> I saw a few conversations on this and one Jira related: https://issues.apache.org/jira/browse/SPARK-4456 .
but I've never seen an answer to this.
> anyone have history on this?



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