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https://issues.apache.org/jira/browse/SPARK-15654?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15306731#comment-15306731
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Jurriaan Pruis commented on SPARK-15654:
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cc [~davies] [~marmbrus] I saw you guys worked on code regarding the
{{FileSourceStrategy}}. Maybe you know more about this issue/how to fix it?
> Reading gzipped files results in duplicate rows
> -----------------------------------------------
>
> Key: SPARK-15654
> URL: https://issues.apache.org/jira/browse/SPARK-15654
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0
> Reporter: Jurriaan Pruis
> Priority: Blocker
>
> When gzipped files are larger then {{spark.sql.files.maxPartitionBytes}}
> reading the file will result in duplicate rows in the dataframe.
> Given an example gzipped wordlist (of 740K bytes):
> {code}
> $ gzcat words.gz |wc -l
> 235886
> {code}
> Reading it using spark results in the following output:
> {code}
> >>> sqlContext.setConf('spark.sql.files.maxPartitionBytes', '1000')
> >>> sqlContext.read.text("/Users/jurriaanpruis/spark/words.gz").count()
> 81244093
> >>> sqlContext.setConf('spark.sql.files.maxPartitionBytes', '10000')
> >>> sqlContext.read.text("/Users/jurriaanpruis/spark/words.gz").count()
> 8348566
> >>> sqlContext.setConf('spark.sql.files.maxPartitionBytes', '100000')
> >>> sqlContext.read.text("/Users/jurriaanpruis/spark/words.gz").count()
> 1051469
> >>> sqlContext.setConf('spark.sql.files.maxPartitionBytes', '1000000')
> >>> sqlContext.read.text("/Users/jurriaanpruis/spark/words.gz").count()
> 235886
> {code}
> You can clearly see how the number of rows scales with the number of
> partitions.
> Somehow the data is duplicated when the number of partitions exceeds one
> (which as seen above approximately scales with the partition size).
> When using distinct you'll get the correct answer:
> {code}
> >>> sqlContext.setConf('spark.sql.files.maxPartitionBytes', '10000')
> >>> sqlContext.read.text("/Users/jurriaanpruis/spark/words.gz").distinct().count()
> 235886
> {code}
> This looks like a pretty serious bug.
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