[jira] [Comment Edited] (SPARK-17998) Reading Parquet files coalesces parts into too few in-memory partitions

["Fernando Pereira (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-17998?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16321234#comment-16321234 ] 

Fernando Pereira edited comment on SPARK-17998 at 1/10/18 10:20 PM:
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It says spark.sql.files.maxPartitionBytes in this very Jira ticket. Try yourself. spark.files.maxPartitionBytes doesnt work, at least not for 2.2.1


was (Author: ferdonline):
It says spark.sql.files.maxPartitionBytes in this very Jira ticket. Try yourself. spark.files.maxPartitionBytes doesnt work

> Reading Parquet files coalesces parts into too few in-memory partitions
> -----------------------------------------------------------------------
>
>                 Key: SPARK-17998
>                 URL: https://issues.apache.org/jira/browse/SPARK-17998
>             Project: Spark
>          Issue Type: Bug
>          Components: PySpark, SQL
>    Affects Versions: 2.0.0, 2.0.1
>         Environment: Spark Standalone Cluster (not "local mode")
> Windows 10 and Windows 7
> Python 3.x
>            Reporter: Shea Parkes
>
> Reading a parquet ~file into a DataFrame is resulting in far too few in-memory partitions.  In prior versions of Spark, the resulting DataFrame would have a number of partitions often equal to the number of parts in the parquet folder.
> Here's a minimal reproducible sample:
> {quote}
> df_first = session.range(start=1, end=100000000, numPartitions=13)
> assert df_first.rdd.getNumPartitions() == 13
> assert session._sc.defaultParallelism == 6
> path_scrap = r"c:\scratch\scrap.parquet"
> df_first.write.parquet(path_scrap)
> df_second = session.read.parquet(path_scrap)
> print(df_second.rdd.getNumPartitions())
> {quote}
> The above shows only 7 partitions in the DataFrame that was created by reading the Parquet back into memory for me.  Why is it no longer just the number of part files in the Parquet folder?  (Which is 13 in the example above.)
> I'm filing this as a bug because it has gotten so bad that we can't work with the underlying RDD without first repartitioning the DataFrame, which is costly and wasteful.  I really doubt this was the intended effect of moving to Spark 2.0.
> I've tried to research where the number of in-memory partitions is determined, but my Scala skills have proven in-adequate.  I'd be happy to dig further if someone could point me in the right direction...



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