Loading data from Spark Structured Streaming into ArrayList - apache-spark

Question

I need to send data from Kafka to Kinesis Firehose. I am processing Kafka data using Spark Structured Streaming. I am not sure how to process the dataset of streaming query into an ArrayList variable - say, recordList - of e.g. 100 records (could be any other value) and then call Firehose API's putRecordBatch(recordList) to put the records into Firehose.

Answer 1

I think you want to check out Foreach and ForeachBatch depending on your Spark Version. ForeachBatch comes in V2.4.0 and foreach is available < V2.4.0. If there is no streaming sink implementation available for Kinesis Firehouse then you should make your own implementation of the ForeachWriter. Databricks has some nice examples of using foreach to create the custom writers.
I haven't ever used Kinesis but here is an example of what your custom sink might look like.
case class MyConfigInfo(info1: String, info2: String)
class KinesisSink(configInfo: MyConfigInfo) extends ForeachWriter[(String, String)] {
val kinesisProducer = _
def open(partitionId: Long,version: Long): Boolean = {
kinesisProducer = //set up the kinesis producer using MyConfigInfo
true
}
def process(value: (String, String)): Unit = {
//ask kinesisProducer to send data
}
def close(errorOrNull: Throwable): Unit = {
//close the kinesis producer
}
}
if you're using that AWS kinesisfirehose API you might do something like this
case class MyConfigInfo(info1: String, info2: String)
class KinesisSink(configInfo: MyConfigInfo) extends ForeachWriter[(String, String)] {
val firehoseClient = _
val req = putRecordBatchRequest = new PutRecordBatchRequest()
val records = 0
val recordLimit = //maybe you need to set this?
def open(partitionId: Long,version: Long): Boolean = {
firehoseClient = //set up the firehose client using MyConfigInfo
true
}
def process(value: (String, String)): Unit = {
//ask fireHose client to send data or batch the request
val record: Record = //create Record out of value
req.setRecords(record)
records = records + 1
if(records >= recordLimit) {
firehoseClient.putRecordBatch(req)
records = 0
}
}
def close(errorOrNull: Throwable): Unit = {
//close the firehose client
//or instead you could put the batch request to the firehose client here but i'm not sure if that's good practice
}
}
Then you'd use it as such
val writer = new KinesisSink(configuration)
val query =
streamingSelectDF
.writeStream
.foreach(writer)
.outputMode("update")
.trigger(ProcessingTime("25 seconds"))
.start()