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From Liang-Chi Hsieh <vii...@gmail.com>
Subject Re: MapOutputTracker.getMapSizesByExecutorId and mutation on the driver?
Date Sat, 24 Dec 2016 07:54:18 GMT

Hi,

I think the comment [1] is only correct for "getStatistics" as it is called
at driver side. It should be added in "getMapSizesByExecutorId" by mistake.



Jacek Laskowski wrote
> Hi,
> 
> I've been reviewing how MapOutputTracker works and can't understand
> the comment [1]:
> 
> // Synchronize on the returned array because, on the driver, it gets
> mutated in place
> 
> How is this possible since "the returned array" is a local value? I'm
> stuck and would appreciate help. Thanks!
> 
> (It also says "Called from executors" [2] so how could the driver be
> involved?!)
> 
> [1]
> https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/MapOutputTracker.scala#L145
> 
> [2]
> https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/MapOutputTracker.scala#L133
> 
> Pozdrawiam,
> Jacek Laskowski
> ----
> https://medium.com/@jaceklaskowski/
> Mastering Apache Spark 2.0 https://bit.ly/mastering-apache-spark
> Follow me at https://twitter.com/jaceklaskowski
> 
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-----
Liang-Chi Hsieh | @viirya 
Spark Technology Center 
http://www.spark.tc/ 
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