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From Amit Joshi <mailtojoshia...@gmail.com>
Subject Re: [Spark Structured Streaming] Processing the data path coming from kafka.
Date Mon, 18 Jan 2021 18:22:03 GMT
Hi Boris,

Thanks for your code block.
I understood what you are trying to achieve in the code.

But content in the file are json records seperated by new line.
And we have to make the dataframe out of it, as some processing has to be
done on it.

Regards
Amit
On Monday, January 18, 2021, Boris Litvak <boris.litvak@skf.com> wrote:

> HI Amit,
>
>
>
> I was thinking along the lines of (python):
>
>
>
>
> @udf(returnType=StringType())
> def reader_udf(filename: str) -> str:
>     with open(filename, "r") as f:
>         return f.read()
>
>
> def run_locally():
>     with utils.build_spark_session("Local", local=True) as spark:
>         df = spark.readStream.csv(r'testdata', schema=StructType([
> StructField('filename', StringType(), True)]))
>         df = df.withColumn('content', reader_udf(col('filename')))
>         q = df.select('content').writeStream.queryName('test').format(
> 'console').start()
>         q.awaitTermination()
>
>
>
> Now each row contains the contents of the files, provided they are not
> large you can foreach() over the df/rdd and do whatever you want with it,
> such as json.loads()/etc.
>
> If you know the shema of the jsons, you can later explode() them into a
> flat DF, ala https://stackoverflow.com/questions/38243717/spark-
> explode-nested-json-with-array-in-scala
>
>
>
> Note that unless I am missing something you cannot access spark session
> from foreach as code is not running on the driver.
>
> Please say if it makes sense or did I miss anything.
>
>
>
> Boris
>
>
>
> *From:* Amit Joshi <mailtojoshiamit@gmail.com>
> *Sent:* Monday, 18 January 2021 17:10
> *To:* Boris Litvak <boris.litvak@skf.com>
> *Cc:* spark-user <user@spark.apache.org>
> *Subject:* Re: [Spark Structured Streaming] Processing the data path
> coming from kafka.
>
>
>
> Hi Boris,
>
>
>
> I need to do processing on the data present in the path.
>
> That is the reason I am trying to make the dataframe.
>
>
>
> Can you please provide the example of your solution?
>
>
>
> Regards
>
> Amit
>
>
>
> On Mon, Jan 18, 2021 at 7:15 PM Boris Litvak <boris.litvak@skf.com> wrote:
>
> Hi Amit,
>
>
>
> Why won’t you just map()/mapXXX() the kafkaDf with the mapping function
> that reads the paths?
>
> Also, do you really have to read the json into an additional dataframe?
>
>
>
> Thanks, Boris
>
>
>
> *From:* Amit Joshi <mailtojoshiamit@gmail.com>
> *Sent:* Monday, 18 January 2021 15:04
> *To:* spark-user <user@spark.apache.org>
> *Subject:* [Spark Structured Streaming] Processing the data path coming
> from kafka.
>
>
>
> Hi ,
>
>
>
> I have a use case where the file path of the json records stored in s3 are
> coming as a kafka
>
> message in kafka. I have to process the data using spark structured
> streaming.
>
>
>
> The design which I thought is as follows:
>
> 1. In kafka Spark structures streaming, read the message containing the
> data path.
>
> 2. Collect the message record in driver. (Messages are small in sizes)
>
> 3. Create the dataframe from the datalocation.
>
>
>
> *kafkaDf*.select(*$"value"*.cast(StringType))
>   .writeStream.foreachBatch((batchDf:DataFrame, batchId:Long) =>  {
>
> //rough code
>
> //collec to driver
>
> *val *records = batchDf.collect()
>
> //create dataframe and process
> records foreach((rec: Row) =>{
>   *println*(*"records:######################"*,rec.toString())
>   val path = rec.getAs[String](*"data_path"*)
>
>   val dfToProcess =spark.read.json(path)
>
>   ....
>
> })
>
> }
>
> I would like to know the views, if this approach is fine? Specifically if there is some
problem with
>
> with creating the dataframe after calling collect.
>
> If there is any better approach, please let know the same.
>
>
>
> Regards
>
> Amit Joshi
>
>

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