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From Jacek Laskowski <>
Subject MapOutputTracker.getMapSizesByExecutorId and mutation on the driver?
Date Fri, 23 Dec 2016 14:13:35 GMT

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?!)



Jacek Laskowski
Mastering Apache Spark 2.0
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