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https://issues.apache.org/jira/browse/SPARK-21137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16065445#comment-16065445
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Steve Loughran commented on SPARK-21137:
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Filed HADOOP-14600.
Looks like a v. old codepath that's not been looked at...and since then the
native lib fstat call should be able to do this, just retain the old code for
when {{NativeCodeLoader.isNativeCodeLoaded() == false}}.
Sam, you said
bq. it's likely that the underlying Hadoop APIs have some yucky code that does
something silly, I have delved down their before and my stomach cannot handle it
oh, it's not so bad. At least you don't have to go near the assembly code bit.
That we are all scared of. Or worse, Kerberos.
Anyway, patches welcome there, with tests
> 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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