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From Pradeep Gollakota <>
Subject Re: Long Shuffle Read Blocked Time
Date Fri, 21 Apr 2017 00:39:35 GMT
Hi All,

It appears that the bottleneck in my job was the EBS volumes. Very high i/o
wait times across the cluster. I was only using 1 volume. Increasing to 4
made it faster.


On Thu, Apr 20, 2017 at 3:12 PM, Pradeep Gollakota <>

> Hi All,
> I have a simple ETL job that reads some data, shuffles it and writes it
> back out. This is running on AWS EMR 5.4.0 using Spark 2.1.0.
> After Stage 0 completes and the job starts Stage 1, I see a huge slowdown
> in the job. The CPU usage is low on the cluster, as is the network I/O.
> From the Spark Stats, I see large values for the Shuffle Read Blocked Time.
> As an example, one of my tasks completed in 18 minutes, but spent 15
> minutes waiting for remote reads.
> I'm not sure why the shuffle is so slow. Are there things I can do to
> increase the performance of the shuffle?
> Thanks,
> Pradeep

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