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From Michael Armbrust <mich...@databricks.com>
Subject Re: Do transformation functions on RDD invoke a Job [sc.runJob]?
Date Mon, 25 Apr 2016 17:29:16 GMT
Spark SQL's query planner has always delayed building the RDD, so has never
needed to eagerly calculate the range boundaries (since Spark 1.0).

On Mon, Apr 25, 2016 at 2:04 AM, Praveen Devarao <praveendrl@in.ibm.com>
wrote:

> Thanks Reynold for the reason as to why sortBykey invokes a Job
>
> When you say "DataFrame/Dataset does not have this issue" is it right to
> assume you are referring to Spark 2.0 or Spark 1.6 DF already has built-in
> it?
>
> Thanking You
>
> ---------------------------------------------------------------------------------
> Praveen Devarao
> Spark Technology Centre
> IBM India Software Labs
>
> ---------------------------------------------------------------------------------
> "Courage doesn't always roar. Sometimes courage is the quiet voice at the
> end of the day saying I will try again"
>
>
>
> From:        Reynold Xin <rxin@databricks.com>
> To:        Praveen Devarao/India/IBM@IBMIN
> Cc:        "dev@spark.apache.org" <dev@spark.apache.org>, user <
> user@spark.apache.org>
> Date:        25/04/2016 11:26 am
> Subject:        Re: Do transformation functions on RDD invoke a Job
> [sc.runJob]?
> ------------------------------
>
>
>
> Usually no - but sortByKey does because it needs the range boundary to be
> built in order to have the RDD. It is a long standing problem that's
> unfortunately very difficult to solve without breaking the RDD API.
>
> In DataFrame/Dataset we don't have this issue though.
>
>
> On Sun, Apr 24, 2016 at 10:54 PM, Praveen Devarao <*praveendrl@in.ibm.com*
> <praveendrl@in.ibm.com>> wrote:
> Hi,
>
>         I have a streaming program with the block as below [ref:
> *https://github.com/agsachin/streamingBenchmark/blob/master/spark-benchmarks/src/main/scala/TwitterStreaming.scala*
> <https://github.com/agsachin/streamingBenchmark/blob/master/spark-benchmarks/src/main/scala/TwitterStreaming.scala>
> ]
>
> *1 val **lines *= *messages*.map(_._2)
> *2 val **hashTags *= *lines*.flatMap(status => status.split(*" "*
> ).filter(_.startsWith(*"#"*)))
>
> *3 val **topCounts60 *= *hashTags*.map((_, 1)).reduceByKey( _ + _ )
> *3a* .map { *case *(topic, count) => (count, topic) }
> *3b* .transform(_.sortByKey(*false*))
>
> *4a**topCounts60*.foreachRDD( rdd => {
> *4b* *val *topList = rdd.take( 10 )
> })
>
>         This batch is triggering 2 jobs...one at line *3b**(sortByKey)* and
> the other at *4b (rdd.take) *I agree that there is a Job triggered on
> line 4b as take() is an action on RDD while as on line 3b sortByKey is just
> a transformation function which as per docs is lazy evaluation...but I see
> that this line uses a RangePartitioner and Rangepartitioner on
> initialization invokes a method called *sketch() *that invokes *collect()*
> triggering a Job.
>
>         My question: Is it expected that sortByKey will invoke a Job...if
> yes, why is sortByKey listed as a transformation and not action. Are there
> any other functions like this that invoke a Job, though they are
> transformations and not actions?
>
>         I am on Spark 1.6
>
> Thanking You
>
> ---------------------------------------------------------------------------------
> Praveen Devarao
> Spark Technology Centre
> IBM India Software Labs
>
> ---------------------------------------------------------------------------------
> "Courage doesn't always roar. Sometimes courage is the quiet voice at the
> end of the day saying I will try again"
>
>
>
>

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