[jira] [Commented] (SPARK-25855) Don't use Erasure Coding for event log files

["Imran Rashid (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-25855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16665487#comment-16665487 ] 

Imran Rashid commented on SPARK-25855:
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cc [~tgraves] [~stevel@apache.org] [~vanzin] who might be interested in this.

Also [~xiaochen] as he helped explain the hdfs side to me and to make sure I didn't make a mistake.

I'll post a pr shortly but would appreciate opinions on whether or not this is a good idea.

> Don't use Erasure Coding for event log files
> --------------------------------------------
>
>                 Key: SPARK-25855
>                 URL: https://issues.apache.org/jira/browse/SPARK-25855
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 2.4.0
>            Reporter: Imran Rashid
>            Priority: Major
>
> While testing spark with hdfs erasure coding (new in hadoop 3), we ran into a bug with the event logs.  The main issue was a bug in hdfs (HDFS-14027), but it did make us wonder whether Spark should be using EC for event log files in general.  Its a poor choice because EC currently implements {{hflush()}} or {{hsync()}} as no-ops, which mean you won't see anything in your event logs until the app is complete.  That isn't necessarily a bug, but isn't really great.  So I think we should ensure EC is always off for event logs.
> IIUC there is *not* a problem with applications which die without properly closing the outputstream.  It'll take a while for the NN to realize the client is gone and finish the block, but the data should get there eventually.
> Also related are SPARK-24787 & SPARK-19531.
> The space savings from EC would be nice as the event logs can get somewhat large, but I think other factors outweigh this.



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