accessLogs.saveAsTextFile(outputDirectory1)
accessList.saveAsTextFile(outputDirectory2)
How to save both the RDD in parallel rather than in series?
import scala.concurrent._
import scala.concurrent.duration._
val rdds = Seq(accessLogs, accessLists)
val dirs = Seq("outputDirectory1", "outputDirectory2")
import ExecutionContext.Implicits.global
val future = Future.sequence(
for ((rdd, dir) <- rdds zip dirs) yield Future(rdd.saveAsTextFile(dir))
)
//Await.ready(future, Duration.Inf) //to wait for rdds to be saved...
Note that despite the name, the method sequence on the Future companion object used above will execute the Futures resulting from the for-comprehension in parallel and not sequentially. This sequence method is essentially an applicative functor sequence.
You can save them in threads.
new Thread() {
override def run(): Unit = {
accessLogs.saveAsTextFile(outputDirectory1)
}
}.start()
new Thread() {
override def run(): Unit = {
accessList.saveAsTextFile(outputDirectory2)
}
}.start()
saveAsTextFile doesn't return anything, so I am not sure why are you setting the return value.
Related
I have multiple files those are independent and need processing by spark. How could I load them into separate rdds in parallel? Thanks!
The coding language is scala.
If you want concurrent reading/processing of RDDs, you could leverage scala.concurrent.Future (or effects in ZIO, Cats etc).
Sample code for loading function is below:
def load(paths: Seq[String], spark: SparkSession)
(implicit ec: ExecutionContext): Seq[Future[RDD[String]]] = {
def loadSinglePath(path: String): Future[RDD[String]] = Future {
spark.sparkContext.textFile(path)
}
paths map loadSinglePath
}
Sample code for using this function:
import scala.concurrent.duration.{Duration, DurationInt}
val sc = SparkSession.builder.master("local[*]").getOrCreate()
implicit val ec = ExecutionContext.global
val result = load(Seq("t1.txt", "t2.txt", "t3.txt"), sc).zipWithIndex
.map { case (rddFuture, idx) =>
rddFuture.map( rdd =>
println(s"Rdd with index $idx has ${rdd.count()}")
)
}
Await.result(Future.sequence(result), 1 hour)
For example purposes, default global ExecutionContext is provided, but it could be configurable to run your code inside the custom one (just replace this implicit val ec with your own ExecutionContext)
I am trying to understand how i should be working with Source.queue & Sink.queue in Akka streaming.
In the little test program that I wrote below I find that I am able to successfully offer 1000 items to the Source.queue.
However, when i wait on the future that should give me the results of pulling all those items off the queue, my
future never completes. Specifically, the message 'print what we pulled off the queue' that we should see at the end
never prints out -- instead we see the error "TimeoutException: Futures timed out after [10 seconds]"
any guidance greatly appreciated !
import akka.actor.ActorSystem
import akka.event.{Logging, LoggingAdapter}
import akka.stream.scaladsl.{Flow, Keep, Sink, Source}
import akka.stream.{ActorMaterializer, Attributes}
import org.scalatest.FunSuite
import scala.collection.immutable
import scala.concurrent.duration._
import scala.concurrent.{Await, ExecutionContext, Future}
class StreamSpec extends FunSuite {
implicit val actorSystem: ActorSystem = ActorSystem()
implicit val materializer: ActorMaterializer = ActorMaterializer()
implicit val log: LoggingAdapter = Logging(actorSystem.eventStream, "basis-test")
implicit val ec: ExecutionContext = actorSystem.dispatcher
case class Req(name: String)
case class Response(
httpVersion: String = "",
method: String = "",
url: String = "",
headers: Map[String, String] = Map())
test("put items on queue then take them off") {
val source = Source.queue[String](128, akka.stream.OverflowStrategy.backpressure)
val flow = Flow[String].map(element => s"Modified $element")
val sink = Sink.queue[String]().withAttributes( Attributes.inputBuffer(128, 128))
val (sourceQueue, sinkQueue) = source.via(flow).toMat(sink)(Keep.both).run()
(1 to 1000).map( i =>
Future {
println("offerd" + i) // I see this print 1000 times as expected
sourceQueue.offer(s"batch-$i")
}
)
println("DONE OFFER FUTURE FIRING")
// Now use the Sink.queue to pull the items we added onto the Source.queue
val seqOfFutures: immutable.Seq[Future[Option[String]]] =
(1 to 1000).map{ i => sinkQueue.pull() }
val futureOfSeq: Future[immutable.Seq[Option[String]]] =
Future.sequence(seqOfFutures)
val seq: immutable.Seq[Option[String]] =
Await.result(futureOfSeq, 10.second)
// unfortunately our future times out here
println("print what we pulled off the queue:" + seq);
}
}
Looking at this again, I realize that I originally set up and posed my question incorrectly.
The test that accompanies my original question launches a wave
of 1000 futures, each of which tries to offer 1 item to the queue.
Then the second step in that test attempts create a 1000-element sequence (seqOfFutures)
where each future is trying to pull a value from the queue.
My theory as to why I was getting time-out errors is that there was some kind of deadlock due to running
out of threads or due to one thread waiting on another but where the waited-on-thread was blocked,
or something like that.
I'm not interested in hunting down the exact cause at this point because I have corrected
things in the code below (see CORRECTED CODE).
In the new code the test that uses the queue is called:
"put items on queue then take them off (with async parallelism) - (3)".
In this test I have a set of 10 tasks which run in parallel to do the 'enequeue' operation.
Then I have another 10 tasks which do the dequeue operation, which involves not only taking
the item off the list, but also calling stringModifyFunc which introduces a 1 ms processing delay.
I also wanted to prove that I got some performance benefit from
launching tasks in parallel and having the task steps communicate by passing their results through a
queue, so test 3 runs as a timed operation, and I found that it takes 1.9 seconds.
Tests (1) and (2) do the same amount of work, but serially -- The first with no intervening queue, and the second
using the queue to pass results between steps. These tests run in 13.6 and 15.6 seconds respectively
(which shows that the queue adds a bit of overhead, but that this is overshadowed by the efficiencies of running tasks in parallel.)
CORRECTED CODE
import akka.{Done, NotUsed}
import akka.actor.ActorSystem
import akka.event.{Logging, LoggingAdapter}
import akka.stream.scaladsl.{Flow, Keep, Sink, Source}
import akka.stream.{ActorMaterializer, Attributes, QueueOfferResult}
import org.scalatest.FunSuite
import scala.concurrent.duration._
import scala.concurrent.{Await, ExecutionContext, Future}
class Speco extends FunSuite {
implicit val actorSystem: ActorSystem = ActorSystem()
implicit val materializer: ActorMaterializer = ActorMaterializer()
implicit val log: LoggingAdapter = Logging(actorSystem.eventStream, "basis-test")
implicit val ec: ExecutionContext = actorSystem.dispatcher
val stringModifyFunc: String => String = element => {
Thread.sleep(1)
s"Modified $element"
}
def setup = {
val source = Source.queue[String](128, akka.stream.OverflowStrategy.backpressure)
val sink = Sink.queue[String]().withAttributes(Attributes.inputBuffer(128, 128))
val (sourceQueue, sinkQueue) = source.toMat(sink)(Keep.both).run()
val offers: Source[String, NotUsed] = Source(
(1 to iterations).map { i =>
s"item-$i"
}
)
(sourceQueue,sinkQueue,offers)
}
val outer = 10
val inner = 1000
val iterations = outer * inner
def timedOperation[T](block : => T) = {
val t0 = System.nanoTime()
val result: T = block // call-by-name
val t1 = System.nanoTime()
println("Elapsed time: " + (t1 - t0) / (1000 * 1000) + " milliseconds")
result
}
test("20k iterations in single threaded loop no queue (1)") {
timedOperation{
(1 to iterations).foreach { i =>
val str = stringModifyFunc(s"tag-${i.toString}")
System.out.println("str:" + str);
}
}
}
test("20k iterations in single threaded loop with queue (2)") {
timedOperation{
val (sourceQueue, sinkQueue, offers) = setup
val resultFuture: Future[Done] = offers.runForeach{ str =>
val itemFuture = for {
_ <- sourceQueue.offer(str)
item <- sinkQueue.pull()
} yield (stringModifyFunc(item.getOrElse("failed")) )
val item = Await.result(itemFuture, 10.second)
System.out.println("item:" + item);
}
val result = Await.result(resultFuture, 20.second)
System.out.println("result:" + result);
}
}
test("put items on queue then take them off (with async parallelism) - (3)") {
timedOperation{
val (sourceQueue, sinkQueue, offers) = setup
def enqueue(str: String) = sourceQueue.offer(str)
def dequeue = {
sinkQueue.pull().map{
maybeStr =>
val str = stringModifyFunc( maybeStr.getOrElse("failed2"))
println(s"dequeud value is $str")
}
}
val offerResults: Source[QueueOfferResult, NotUsed] =
offers.mapAsyncUnordered(10){ string => enqueue(string)}
val dequeueResults: Source[Unit, NotUsed] = offerResults.mapAsyncUnordered(10){ _ => dequeue }
val runAll: Future[Done] = dequeueResults.runForeach(u => u)
Await.result(runAll, 20.second)
}
}
}
I'm writing a Scala program to read objects matching a certain prefix on S3.
At the moment, I'm testing it on my Macbook Pro and it takes 270ms (avg. over 1000 trials) to hit S3, retrieve the 10 objects (avg. size of object 150Kb) and process it to print the output.
Here's my code:
val myBucket = "my-test-bucket"
val myPrefix = "t"
val startTime = System.currentTimeMillis()
//Can I make listObject parallel?
val listObjRequest: ListObjectsRequest = new ListObjectsRequest().withBucketName(myBucket)
val listObjResult: Seq[String] = s3.listObjects(listObjRequest).getObjectSummaries.par.toIndexedSeq.map(_.getKey).filter(_ matches s"./.*${myPrefix}.*/*")
//Can I make forEach parallel?
listObjResult foreach println //Could be any function
println(s"Total time: ${System.currentTimeMillis() - startTime}ms")
In the big scheme of things, I've got to sift through 50Gb of data (approx. 350K nested objects) and delete objects following a certain prefix (approx. 40K objects).
Hardware considerations aside, what can I do to optimize my code?
Thanks!
A possible solution would be to batch the request objects and send a request for batch deletion in S3. You can group the objects to delete and then parallalize the mapping over the parallel collection:
import com.amazonaws.services.s3.AmazonS3Client
import com.amazonaws.services.s3.model.DeleteObjectsRequest.KeyVersion
import com.amazonaws.services.s3.model.{DeleteObjectsRequest, DeleteObjectsResult}
import scala.collection.JavaConverters._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent._
import scala.util.Try
object AmazonBatchDeletion {
def main(args: Array[String]): Unit = {
val filesToDelete: List[String] = ???
val numOfGroups: Int = ???
val deletionAttempts: Iterator[Future[Try[DeleteObjectsResult]]] =
filesToDelete
.grouped(numOfGroups)
.map(groupToDelete => Future {
blocking {
deleteFilesInBatch(groupToDelete, "bucketName")
}
})
val result: Future[Iterator[Try[DeleteObjectsResult]]] =
Future.sequence(deletionAttempts)
// TODO: make sure deletion was successful.
// Recover if needed form faulted futures.
}
def deleteFilesInBatch(filesToDelete: List[String],
bucketName: String): Try[DeleteObjectsResult] = {
val amazonClient = new AmazonS3Client()
val deleteObjectsRequest = new DeleteObjectsRequest(bucketName)
deleteObjectsRequest.setKeys(filesToDelete.map(new KeyVersion(_)).asJava)
Try {
amazonClient.deleteObjects(deleteObjectsRequest)
}
}
}
I m using dispatch library in my sbt project. When I initialize three future and run them it is working perfectly But I increase one more future then it goes to a loop.
My code:
//Initializing Futures
def sequenceOfFutures() ={
var pageNumber: Int = 1
var list ={Seq(Future{})}
for (pageNumber <- 1 to 4) {
list ++= {
Seq(
Future {
str= getRequestFunction(pageNumber);
GlobalObjects.sleep(Random.nextInt(1500));
}
)
}
}
Future.sequence(list)
}
Await.result(sequenceOfFutures, Duration.Inf)
And then getRequestionFunction(pageNumber) code:
def getRequestionFunction(pageNumber)={
val h=Http("scala.org", as_str)
while(h.isComplete){
Thread,sleep(1500);
}
}
I tried based on one suggestion from How to configure a fine tuned thread pool for futures?
I added this to my code:
import java.util.concurrent.Executors
import scala.concurrent._
implicit val ec = new ExecutionContext {
val threadPool = Executors.newFixedThreadPool(1000);
def execute(runnable: Runnable) {
threadPool.submit(runnable)
}
def reportFailure(t: Throwable) {}
}// Still didn't work
So when I use more than four Futures then it keeps await forever. Is there some solution to fix it?
But it didn't work Could someone please suggest how to solve this issue?
I wrote this method:
import scala.concurrent._
import ExecutionContext.Implicits.global
import scala.util.{ Success, Failure }
object FuturesSequence extends App {
val f1 = future {
1
}
val f2 = future {
2
}
val lf = List(f1, f2)
val seq = Future.sequence(lf)
seq.onSuccess {
case l => println(l)
}
}
I was expecting Future.sequence to gather a List[Future] into a Future[List] and then wait for every futures (f1 and f2 in my case) to complete before calling onSuccess on the Future[List] seq in my case.
But after many runs of this code, it prints "List(1, 2)" only once in a while and I can't figure out why it does not work as expected.
Try this for once,
import scala.concurrent._
import java.util.concurrent.Executors
import scala.util.{ Success, Failure }
object FuturesSequence extends App {
implicit val exec = ExecutionContext.fromExecutor(Executors.newCachedThreadPool)
val f1 = future {
1
}
val f2 = future {
2
}
val lf = List(f1, f2)
val seq = Future.sequence(lf)
seq.onSuccess {
case l => println(l)
}
}
This will always print List(1,2). The reason is simple, the exec above is an ExecutionContext of threads (not daemon threads) where as in your example the ExecutionContext was the default one implicitly taken from ExecutionContext.Implicits.global which contains daemon threads.
Hence being daemon, the process doesn't wait for seq future to be completed and terminates. if at all seq does get completed then it prints. But that doesn't happen always
The application is exiting before the future is completes.
You need to block until the future has completed. This can be achieved in a variety of ways, including changing the ExecutionContext, instantiating a new ThreadPool, Thread.sleep etc, or by using methods on scala.concurrent.Await
The simplest way for your code is by using Await.ready. This blocks on a future for a specified amount of time. In the modified code below, the application waits for 5 seconds before exiting.
Note also, the extra import scala.concurrent.duration so we can specify the time to wait.
import scala.concurrent._
import scala.concurrent.duration._
import java.util.concurrent.Executors
import scala.util.{ Success, Failure }
object FuturesSequence extends App {
val f1 = future {
1
}
val f2 = future {
2
}
val lf = List(f1, f2)
val seq = Future.sequence(lf)
seq.onSuccess {
case l => println(l)
}
Await.ready(seq, 5 seconds)
}
By using Await.result instead, you can skip the onSuccess method too, as it will return the resulting list to you.
Example:
val seq: List[Int] = Await.result(Future.sequence(lf), 5 seconds)
println(seq)