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From Gourav Sengupta <gourav.sengu...@gmail.com>
Subject Re: Issues with large schema tables
Date Thu, 08 Mar 2018 15:01:45 GMT
Hi Ballas,

in Data Science terms you have 4500 variables without correlations or which
are independent of each other. In Data Modelling terms you have an entity
with 4500 properties. I have worked on hair splitting financial products,
even they do not have properties of a financial product with more than 800
properties through out its lifecycle.

I think that the best way to approach your problem is not to think it as a
data engineering problem, but a data architecture problem. Please apply
dimensionality reduction, data modelling and MDM to the data before
processing it.


Regards,
Gourav

On Wed, Mar 7, 2018 at 6:34 PM, Ballas, Ryan W <ryan.ballas@optum.com>
wrote:

> Hello All,
>
>
>
> Our team is having a lot of issues with the Spark API particularly with
> large schema tables. We currently have a program written in Scala that
> utilizes the Apache spark API to create two tables from raw files. We have
> one particularly very large raw data file that contains around ~4700
> columns and ~200,000 rows. Every week we get a new file that shows the
> updates, inserts and deletes that happened in the last week. Our program
> will create two files – a master file and a history file. The master file
> will be the most up to date version of this table while the history table
> shows all changes inserts and updates that happened to this table and
> showing what changed. For example, if we have the following schema where A
> and B are unique:
>
>
>
> Week 1
> Week 2
>
> *A*             *B*             C
>                                  *A*             *B*             C
>
> 1              2              3
>                 1              2              4
>
>
>
> Then the master table will now be
>
> *A*             *B*             C
>
> 1              2              4
>
>
>
> and History table will be
>
> *A             B*             change_column  change_type
> old_value              new_value
>
> 1              2              C                              Update
>                 3                              4
>
>
>
> This process is working flawlessly for shorter schema tables. We have a
> table that has 300 columns but over 100,000,000 rows and this code still
> runs. The process above for the larger schema table runs for around 15
> hours, and then crashes with the following error:
>
>
>
> Exception in thread "main" java.lang.StackOverflowError
>
>         at scala.collection.generic.Growable$class.loop$1(
> Growable.scala:52)
>
>         at scala.collection.generic.Growable$class.$plus$plus$eq(
> Growable.scala:57)
>
>         at scala.collection.mutable.ListBuffer.$plus$plus$eq(
> ListBuffer.scala:183)
>
>         at scala.collection.mutable.ListBuffer.$plus$plus$eq(
> ListBuffer.scala:45)
>
>         at scala.collection.TraversableLike$$anonfun$flatMap$1.apply(
> TraversableLike.scala:241)
>
>         at scala.collection.TraversableLike$$anonfun$flatMap$1.apply(
> TraversableLike.scala:241)
>
>         at scala.collection.immutable.List.foreach(List.scala:381)
>
>         at scala.collection.TraversableLike$class.flatMap(
> TraversableLike.scala:241)
>
>         at scala.collection.immutable.List.flatMap(List.scala:344)
>
> …
>
>
>
> Some other notes… This is running on a very large MAPR cluster. We have
> tried running the job with upwards of ½ a TB of RAM and this still happens.
> All of our other smaller schema tables run except for this one.
>
>
>
> Here is a code example that takes around 4 hours to run for this larger
> table, but runs in 20 seconds for other tables:
>
>
>
> *var *dataframe_result = dataframe1.join(*broadcast*(dataframe2), *Seq*(
> listOfUniqueIds:_*)).repartition(100).cache()
>
>
>
> We have tried all of the following with no success:
>
>    - Using hash broad-cast joins (dataframe2 is smaller, dataframe1 is
>    huge)
>    - Repartioining on different numbers, as well as not repartitioning at
>    all
>    - Caching the result of the dataframe (we originally did not do this).
>
>
>
> What is causing this error and how do we go about fixing it? This code
> just takes in 1 parameter (the table to run) so it’s the exact same code
> for every table. It runs flawlessly for every other table except for this
> one. The only thing different between this table and all the other ones is
> the number of columns. This has the most columns at 4700 where the second
> most is 800.
>
>
>
> If anyone has any ideas on how to fix this it would be greatly
> appreciated. Thank you in advance for the help!!
>
>
>
>
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