I actually asked the same thing a couple of weeks ago.
Apparently, when you create a structured streaming plan, it is different than
the batch plan and is fixed in order to properly aggregate. If you perform most
operations on the dataframe it will recalculate the plan as a batch plan and
will therefore not work properly. Therefore, you must either collect or turn to
RDD and then create a new dataframe from the RDD.
It would be very useful IMO if we can "freeze" the plan for the input portion
and work as if it was a new dataframe (similar to turning it to RDD and then
creating a new dataframe from the RDD but without the overhead of converting to
RDD and back to dataframe), however, this is not currently possible.
Thanks,
Assaf.
From: Jacek Laskowski [via Apache Spark Developers List]
[mailto:ml+s1001551n21930...@n3.nabble.com]
Sent: Friday, July 07, 2017 11:44 AM
To: Mendelson, Assaf
Subject: [SS] Why does ConsoleSink's addBatch convert input DataFrame to show
it?
Hi,
Just noticed that the input DataFrame is collect'ed and then
parallelize'd simply to show it to the console [1]. Why so many fairly
expensive operations for show?
I'd appreciate some help understanding this code. Thanks.
[1]
https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/console.scala#L51-L53
Pozdrawiam,
Jacek Laskowski
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