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https://issues.apache.org/jira/browse/SPARK-21137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16065515#comment-16065515
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Steve Loughran commented on SPARK-21137:
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bq. so it is something that could be optimized in the Hadoop API, and seems
somewhat specific to a local filesystem.
yeah, its something unique to the local FS (maybe things which extend it, like
glusterfs —[~jayunit100] ?). Fix would be straightforward if someone goes down
to it & writes the test. Ideally a scale one which creates 1K+ small files and
then measures the diff in times between listStatus as a before/after.
> Spark reads many small files slowly
> -----------------------------------
>
> Key: SPARK-21137
> URL: https://issues.apache.org/jira/browse/SPARK-21137
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.1.1
> Reporter: sam
> Priority: Minor
>
> A very common use case in big data is to read a large number of small files.
> For example the Enron email dataset has 1,227,645 small files.
> When one tries to read this data using Spark one will hit many issues.
> Firstly, even if the data is small (each file only say 1K) any job can take a
> very long time (I have a simple job that has been running for 3 hours and has
> not yet got to the point of starting any tasks, I doubt if it will ever
> finish).
> It seems all the code in Spark that manages file listing is single threaded
> and not well optimised. When I hand crank the code and don't use Spark, my
> job runs much faster.
> Is it possible that I'm missing some configuration option? It seems kinda
> surprising to me that Spark cannot read Enron data given that it's such a
> quintessential example.
> So it takes 1 hour to output a line "1,227,645 input paths to process", it
> then takes another hour to output the same line. Then it outputs a CSV of all
> the input paths (so creates a text storm).
> Now it's been stuck on the following:
> {code}
> 17/06/19 09:31:07 INFO LzoCodec: Successfully loaded & initialized native-lzo
> library [hadoop-lzo rev 154f1ef53e2d6ed126b0957d7995e0a610947608]
> {code}
> for 2.5 hours.
> So I've provided full reproduce steps here (including code and cluster setup)
> https://github.com/samthebest/scenron, scroll down to "Bug In Spark". You can
> easily just clone, and follow the README to reproduce exactly!
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