because `coalesce` gets propagated further up in the DAG in the last stage, so your last stage only has one task.

You need to break your DAG so your expensive operations would be in a previous stage before the stage with `.coalesce(1)`

On Fri, Mar 9, 2018 at 5:23 AM, Md. Rezaul Karim <rezaul.karim@insight-centre.org> wrote:
Dear All,

I have a tiny CSV file, which is around 250MB. There are only 30 columns in the DataFrame. Now I'm trying to save the pre-processed DataFrame as an another CSV file on disk for later usage.

However, I'm getting pissed off as writing the resultant DataFrame is taking too long, which is about 4 to 5 hours. Nevertheless, the size of the file written on the disk is about 58GB! 

Here's the sample code that I tried:

# Using repartition()
myDF.repartition(1).write.format("com.databricks.spark.csv").save("data/file.csv")

# Using coalesce()
myDF. coalesce(1).write.format("com.databricks.spark.csv").save("data/file.csv")


Any better suggestion?



----
Md. Rezaul Karim, BSc, MSc
Research Scientist, Fraunhofer FIT, Germany

Ph.D. Researcher, Information Systems, RWTH Aachen University, Germany

eMail: rezaul.karim@fit.fraunhofer.de
Tel: +49 241 80-21527




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