Interview Questions and Answers

Transformations are operations that create a new RDD, while actions are operations that return a value to the driver program or write data to an external storage system.

Example:

val mappedRDD = inputRDD.map(x => x * 2)
val result = mappedRDD.reduce((x, y) => x + y)

Spark's lineage graph (DAG) is a directed acyclic graph that represents the sequence of transformations and actions on RDDs. It helps in recovering lost data in case of node failure.

Example:

val filteredRDD = inputRDD.filter(x => x > 0)
filteredRDD.toDebugString

Partitions are basic units of parallelism in Spark. They represent the logical division of data across the nodes in a cluster, and each partition is processed independently.

Example:

val inputRDD = sc.parallelize(Seq(1, 2, 3, 4, 5), 2)

A Spark Executor is a process responsible for executing tasks on a worker node. Executors are launched at the beginning of a Spark application and run tasks until the application completes or encounters an error.

Example:

spark-submit --master yarn --deploy-mode client --num-executors 3 mySparkApp.jar

A Broadcast variable is a read-only variable cached on each worker node. It is used to efficiently distribute large read-only data structures, such as lookup tables, to all tasks in a Spark job.

Example:

val broadcastVar = sc.broadcast(Array(1, 2, 3))

Spark SQL is a Spark module for structured data processing. It provides a programming interface for data manipulation using SQL, as well as a DataFrame API for processing structured and semi-structured data.

Example:

val df = spark.sql("SELECT * FROM table")

You can persist an RDD using the persist() or cache() method. It allows you to store the RDD's data in memory or on disk for faster access.

Example:

val cachedRDD = inputRDD.persist(StorageLevel.MEMORY_ONLY)

Narrow transformations involve operations where each input partition contributes to only one output partition. Wide transformations involve operations where multiple input partitions contribute to multiple output partitions.

Example:

Narrow: map, filter
Wide: groupByKey, reduceByKey

Spark Streaming is an extension of the core Spark API that enables scalable, high-throughput, fault-tolerant stream processing of live data streams. It allows processing real-time data using batch processing capabilities of Spark.

Example:

val streamingContext = new StreamingContext(sparkContext, Seconds(1))

Spark uses Java's Object Serialization to serialize data between the Spark Driver and Executors. Efficient serialization is crucial for optimizing data transfer and reducing network overhead.

Example:

sparkConf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer")

An accumulator is a variable that can be added to and is used in Spark to implement counters and sums in a parallel and fault-tolerant manner across distributed tasks.

Example:

val accumulator = sc.longAccumulator("MyAccumulator")

The Spark DAG represents the logical execution plan of transformations and actions in a Spark application. It is a graph of stages, where each stage contains a sequence of tasks that can be executed in parallel.

Example:

val dag = inputRDD.map(x => x * 2).toDebugString

A task is the smallest unit of work in Spark, representing the execution of a transformation or action on a partition of data. Tasks are scheduled by the Spark Scheduler on Spark Executors.

Example:

val taskResult = executor.runTask(taskID, taskInfo)

Spark MLlib is Spark's machine learning library, providing scalable implementations of various machine learning algorithms and tools for building and evaluating machine learning models.

Example:

val model = new RandomForestClassifier().fit(trainingData)