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https://issues.apache.org/jira/browse/SPARK-5081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14486601#comment-14486601
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Josh Rosen commented on SPARK-5081:
-----------------------------------
I wrote a microbenchmark for snappy-java which shows an increased in compressed
data sizes between the pre- and post-1.2 Snappy versions. I ran a bisect across
published snappy-java releases and think that I've narrowed the problem down to
a single patch.
I've opened https://github.com/xerial/snappy-java/issues/100 to investigate
this upstream.
Note that this may not end up fully explaining this issue, since there could be
multiple contributors to the shuffle file write size increase, but it seems
suspicious.
> Shuffle write increases
> -----------------------
>
> Key: SPARK-5081
> URL: https://issues.apache.org/jira/browse/SPARK-5081
> Project: Spark
> Issue Type: Bug
> Components: Shuffle
> Affects Versions: 1.2.0
> Reporter: Kevin Jung
> Priority: Critical
> Attachments: Spark_Debug.pdf, diff.txt
>
>
> The size of shuffle write showing in spark web UI is much different when I
> execute same spark job with same input data in both spark 1.1 and spark 1.2.
> At sortBy stage, the size of shuffle write is 98.1MB in spark 1.1 but 146.9MB
> in spark 1.2.
> I set spark.shuffle.manager option to hash because it's default value is
> changed but spark 1.2 still writes shuffle output more than spark 1.1.
> It can increase disk I/O overhead exponentially as the input file gets bigger
> and it causes the jobs take more time to complete.
> In the case of about 100GB input, for example, the size of shuffle write is
> 39.7GB in spark 1.1 but 91.0GB in spark 1.2.
> spark 1.1
> ||Stage Id||Description||Input||Shuffle Read||Shuffle Write||
> |9|saveAsTextFile| |1169.4KB| |
> |12|combineByKey| |1265.4KB|1275.0KB|
> |6|sortByKey| |1276.5KB| |
> |8|mapPartitions| |91.0MB|1383.1KB|
> |4|apply| |89.4MB| |
> |5|sortBy|155.6MB| |98.1MB|
> |3|sortBy|155.6MB| | |
> |1|collect| |2.1MB| |
> |2|mapValues|155.6MB| |2.2MB|
> |0|first|184.4KB| | |
> spark 1.2
> ||Stage Id||Description||Input||Shuffle Read||Shuffle Write||
> |12|saveAsTextFile| |1170.2KB| |
> |11|combineByKey| |1264.5KB|1275.0KB|
> |8|sortByKey| |1273.6KB| |
> |7|mapPartitions| |134.5MB|1383.1KB|
> |5|zipWithIndex| |132.5MB| |
> |4|sortBy|155.6MB| |146.9MB|
> |3|sortBy|155.6MB| | |
> |2|collect| |2.0MB| |
> |1|mapValues|155.6MB| |2.2MB|
> |0|first|184.4KB| | |
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