Top 40 Apache Spark Interview Questions and Answers

Do you want to get a job using your Apache Spark skills, do you? How ambitious! Are you ready? You’re going to have to get the job first, and that means an interview. And questions. Lots of them. But fear not, we’re here to help you. We’re providing top Apache Spark interview questions and answers for you to study.

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It’s no secret the demand for Apache Spark is rising rapidly. With companies like Shopify, Amazon, and Alibaba already implementing it, you can only expect more to adopt this large-scale data processing engine in 2019. Because it can handle event streaming and process data faster than Hadoop MapReduce, it’s quickly becoming the hot skill to have. And the big bucks are in it. According to the 2015 Data Science Salary Survey by O’Reilly, in 2016, people who could use Apache Spark made an average of $11,000 more than programmers who didn’t. 

Apache Spark is a unified analytics engine for processing large volumes of data. It can run workloads 100 times faster and offers over 80 high-level operators that make it easy to build parallel apps. Spark can run on Hadoop, Apache Mesos, Kubernetes, standalone, or in the cloud, and can access data from multiple sources.

And this article covers the most important Apache Spark Interview questions that you might face in your next interview. The questions have been segregated into different sections based on the various components of Apache Spark and surely after going through this article, you will be able to answer the questions asked in your interview.

Nice, huh? What are you waiting for? Know the answers to these common Apache Spark interview questions and land that job. You can do it, Sparky.

Apache Spark Interview Questions

The Apache Spark interview questions have been divided into two parts:

• Apache Spark Interview Questions for Beginners
• Apache Spark Interview Questions for Experienced

Apache Spark Interview Questions for Beginners

1. How is Apache Spark different from MapReduce?

Apache Spark	MapReduce
Spark processes data in batches as well as in real-time	MapReduce processes data in batches only
Spark runs almost 100 times faster than Hadoop MapReduce	Hadoop MapReduce is slower when it comes to large scale data processing
Spark stores data in the RAM i.e. in-memory. So, it is easier to retrieve it	Hadoop MapReduce data is stored in HDFS and hence takes a long time to retrieve the data
Spark provides caching and in-memory data storage	Hadoop is highly disk-dependent

2. What are the important components of the Spark ecosystem?

Apache Spark has 3 main categories that comprise its ecosystem. Those are:

• Language support: Spark can integrate with different languages to applications and perform analytics. These languages are Java, Python, Scala, and R.
• Core Components: Spark supports 5 main core components. There are Spark Core, Spark SQL, Spark Streaming, Spark MLlib, and GraphX.
• Cluster Management: Spark can be run in 3 environments. Those are the Standalone cluster, Apache Mesos, and YARN.

3. Explain how Spark runs applications with the help of its architecture.

Spark applications run as independent processes that are coordinated by the SparkSession object in the driver program. The resource manager or cluster manager assigns tasks to the worker nodes with one task per partition. Iterative algorithms apply operations repeatedly to the data so they can benefit from caching datasets across iterations. A task applies its unit of work to the dataset in its partition and outputs a new partition dataset. Finally, the results are sent back to the driver application or can be saved to the disk.

4. What are the different cluster managers available in Apache Spark?

• Standalone Mode: By default, applications submitted to the standalone mode cluster will run in FIFO order, and each application will try to use all available nodes. You can launch a standalone cluster either manually, by starting a master and workers by hand, or use our provided launch scripts. It is also possible to run these daemons on a single machine for testing.
• Apache Mesos: Apache Mesos is an open-source project to manage computer clusters, and can also run Hadoop applications. The advantages of deploying Spark with Mesos include dynamic partitioning between Spark and other frameworks as well as scalable partitioning between multiple instances of Spark.
• Hadoop YARN: Apache YARN is the cluster resource manager of Hadoop 2. Spark can be run on YARN as well.
• Kubernetes: Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.

5. What is the significance of Resilient Distributed Datasets in Spark?

Resilient Distributed Datasets are the fundamental data structure of Apache Spark. It is embedded in Spark Core. RDDs are immutable, fault-tolerant, distributed collections of objects that can be operated on in parallel.RDD’s are split into partitions and can be executed on different nodes of a cluster.

RDDs are created by either transformation of existing RDDs or by loading an external dataset from stable storage like HDFS or HBase.

Here is how the architecture of RDD looks like:

6. What is a lazy evaluation in Spark?

When Spark operates on any dataset, it remembers the instructions. When a transformation such as a map() is called on an RDD, the operation is not performed instantly. Transformations in Spark are not evaluated until you perform an action, which aids in optimizing the overall data processing workflow, known as lazy evaluation.

7. What makes Spark good at low latency workloads like graph processing and Machine Learning?

Apache Spark stores data in-memory for faster processing and building machine learning models. Machine Learning algorithms require multiple iterations and different conceptual steps to create an optimal model. Graph algorithms traverse through all the nodes and edges to generate a graph. These low latency workloads that need multiple iterations can lead to increased performance.

8. How can you trigger automatic clean-ups in Spark to handle accumulated metadata?

To trigger the clean-ups, you need to set the parameter spark.cleaner.ttlx.

9. How can you connect Spark to Apache Mesos?

There are a total of 4 steps that can help you connect Spark to Apache Mesos.

• Configure the Spark Driver program to connect with Apache Mesos
• Put the Spark binary package in a location accessible by Mesos
• Install Spark in the same location as that of the Apache Mesos
• Configure the spark.mesos.executor.home property for pointing to the location where Spark is installed

10. What is a Parquet file and what are its advantages?

Parquet is a columnar format that is supported by several data processing systems. With the Parquet file, Spark can perform both read and write operations. 

Some of the advantages of having a Parquet file are:

• It enables you to fetch specific columns for access.
• It consumes less space
• It follows the type-specific encoding
• It supports limited I/O operations

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11. What is shuffling in Spark? When does it occur?

Shuffling is the process of redistributing data across partitions that may lead to data movement across the executors. The shuffle operation is implemented differently in Spark compared to Hadoop. 

Shuffling has 2 important compression parameters:

spark.shuffle.compress – checks whether the engine would compress shuffle outputs or not spark.shuffle.spill.compress – decides whether to compress intermediate shuffle spill files or not

It occurs while joining two tables or while performing byKey operations such as GroupByKey or ReduceByKey

12. What is the use of coalesce in Spark?

Spark uses a coalesce method to reduce the number of partitions in a DataFrame.

Suppose you want to read data from a CSV file into an RDD having four partitions.

This is how a filter operation is performed to remove all the multiple of 10 from the data.

The RDD has some empty partitions. It makes sense to reduce the number of partitions, which can be achieved by using coalesce.

This is how the resultant RDD would look like after applying to coalesce.

13. How can you calculate the executor memory?

Consider the following cluster information:

Here is the number of core identification:

To calculate the number of executor identification:

14. What are the various functionalities supported by Spark Core?

Spark Core is the engine for parallel and distributed processing of large data sets. The various functionalities supported by Spark Core include:

• Scheduling and monitoring jobs
• Memory management
• Fault recovery
• Task dispatching

15. How do you convert a Spark RDD into a DataFrame?

There are 2 ways to convert a Spark RDD into a DataFrame:

• Using the helper function - toDF

import com.mapr.db.spark.sql._

val df = sc.loadFromMapRDB(<table-name>)

.where(field(“first_name”) === “Peter”)

.select(“_id”, “first_name”).toDF()

• Using SparkSession.createDataFrame

You can convert an RDD[Row] to a DataFrame by

calling createDataFrame on a SparkSession object

def createDataFrame(RDD, schema:StructType)

16. Explain the types of operations supported by RDDs.

RDDs support 2 types of operation:

Transformations: Transformations are operations that are performed on an RDD to create a new RDD containing the results (Example: map, filter, join, union)

Actions: Actions are operations that return a value after running a computation on an RDD (Example: reduce, first, count) 

17. What is a Lineage Graph?

A Lineage Graph is a dependencies graph between the existing RDD and the new RDD. It means that all the dependencies between the RDD will be recorded in a graph,  rather than the original data.

The need for an RDD lineage graph happens when we want to compute a new RDD or if we want to recover the lost data from the lost persisted RDD. Spark does not support data replication in memory. So, if any data is lost, it can be rebuilt using RDD lineage. It is also called an RDD operator graph or RDD dependency graph.

18. What do you understand about DStreams in Spark?

Discretized Streams is the basic abstraction provided by Spark Streaming. 

It represents a continuous stream of data that is either in the form of an input source or processed data stream generated by transforming the input stream.

19. Explain Caching in Spark Streaming.

Caching also known as Persistence is an optimization technique for Spark computations. Similar to RDDs, DStreams also allow developers to persist the stream’s data in memory. That is, using the persist() method on a DStream will automatically persist every RDD of that DStream in memory. It helps to save interim partial results so they can be reused in subsequent stages.

The default persistence level is set to replicate the data to two nodes for fault-tolerance, and for input streams that receive data over the network.

20. What is the need for broadcast variables in Spark?

Broadcast variables allow the programmer to keep a read-only variable cached on each machine rather than shipping a copy of it with tasks. They can be used to give every node a copy of a large input dataset in an efficient manner. Spark distributes broadcast variables using efficient broadcast algorithms to reduce communication costs.

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

broadcastVar: org.apache.spark.broadcast.Broadcast[Array[Int]] = Broadcast(0)

scala> broadcastVar.value

res0: Array[Int] = Array(1, 2, 3)

Apache Spark Interview Questions for Experienced

21. How to programmatically specify a schema for DataFrame?

DataFrame can be created programmatically with three steps:

• Create an RDD of Rows from the original RDD;
• Create the schema represented by a StructType matching the structure of Rows in the RDD created in Step 1.
• Apply the schema to the RDD of Rows via createDataFrame method provided by SparkSession.

22. Which transformation returns a new DStream by selecting only those records of the source DStream for which the function returns true?

1. map(func)

2. transform(func)

3. filter(func)

4. count()

The correct answer is c) filter(func).

23. Does Apache Spark provide checkpoints?

Yes, Apache Spark provides an API for adding and managing checkpoints. Checkpointing is the process of making streaming applications resilient to failures. It allows you to save the data and metadata into a checkpointing directory. In case of a failure, the spark can recover this data and start from wherever it has stopped.

There are 2 types of data for which we can use checkpointing in Spark.

Metadata Checkpointing: Metadata means the data about data. It refers to saving the metadata to fault-tolerant storage like HDFS. Metadata includes configurations, DStream operations, and incomplete batches.

Data Checkpointing: Here, we save the RDD to reliable storage because its need arises in some of the stateful transformations. In this case, the upcoming RDD depends on the RDDs of previous batches. 

24. What do you mean by sliding window operation?

Controlling the transmission of data packets between multiple computer networks is done by the sliding window. Spark Streaming library provides windowed computations where the transformations on RDDs are applied over a sliding window of data.

25. What are the different levels of persistence in Spark?

DISK_ONLY - Stores the RDD partitions only on the disk

MEMORY_ONLY_SER - Stores the RDD as serialized Java objects with a one-byte array per partition

MEMORY_ONLY - Stores the RDD as deserialized Java objects in the JVM. If the RDD is not able to fit in the memory available, some partitions won’t be cached

OFF_HEAP - Works like MEMORY_ONLY_SER but stores the data in off-heap memory

MEMORY_AND_DISK - Stores RDD as deserialized Java objects in the JVM. In case the RDD is not able to fit in the memory, additional partitions are stored on the disk

MEMORY_AND_DISK_SER - Identical to MEMORY_ONLY_SER with the exception of storing partitions not able to fit in the memory to the disk

26. What is the difference between map and flatMap transformation in Spark Streaming?

map()	flatMap()
A map function returns a new DStream by passing each element of the source DStream through a function func	It is similar to the map function and applies to each element of RDD and it returns the result as a new RDD
Spark Map function takes one element as an input process it according to custom code (specified by the developer) and returns one element at a time	FlatMap allows returning 0, 1, or more elements from the map function. In the FlatMap operation

27. How would you compute the total count of unique words in Spark?

1. Load the text file as RDD:

sc.textFile(“hdfs://Hadoop/user/test_file.txt”);

2. Function that breaks each line into words:

def toWords(line):

return line.split();

3. Run the toWords function on each element of RDD in Spark as flatMap transformation:

words = line.flatMap(toWords);

4. Convert each word into (key,value) pair:

def toTuple(word):

return (word, 1);

wordTuple = words.map(toTuple);

5. Perform reduceByKey() action:

def sum(x, y):

return x+y:

counts = wordsTuple.reduceByKey(sum) 

6. Print:

counts.collect()

28. Suppose you have a huge text file. How will you check if a particular keyword exists using Spark?

lines = sc.textFile(“hdfs://Hadoop/user/test_file.txt”);

def isFound(line):

if line.find(“my_keyword”) > -1

return 1

return 0

foundBits = lines.map(isFound);

sum = foundBits.reduce(sum);

if sum > 0:

print “Found”

else:

print “Not Found”;

29. What is the role of accumulators in Spark?

Accumulators are variables used for aggregating information across the executors. This information can be about the data or API diagnosis like how many records are corrupted or how many times a library API was called.

30. What are the different MLlib tools available in Spark?

• ML Algorithms: Classification, Regression, Clustering, and Collaborative filtering
• Featurization: Feature extraction, Transformation, Dimensionality reduction, 

and Selection

• Pipelines: Tools for constructing, evaluating, and tuning ML pipelines
• Persistence: Saving and loading algorithms, models, and pipelines
• Utilities: Linear algebra, statistics, data handling

31. What are the different data types supported by Spark MLlib?

Spark MLlib supports local vectors and matrices stored on a single machine, as well as distributed matrices.

Local Vector: MLlib supports two types of local vectors - dense and sparse

Example: vector(1.0, 0.0, 3.0)

dense format: [1.0, 0.0, 3.0]

sparse format: (3, [0, 2]. [1.0, 3.0]) 

Labeled point: A labeled point is a local vector, either dense or sparse that is associated with a label/response.

Example: In binary classification, a label should be either 0 (negative) or 1 (positive)

Local Matrix: A local matrix has integer type row and column indices, and double type values that are stored in a single machine.

Distributed Matrix: A distributed matrix has long-type row and column indices and double-type values, and is stored in a distributed manner in one or more RDDs. 

Types of the distributed matrix:

• RowMatrix
• IndexedRowMatrix
• CoordinatedMatrix

32. What is a Sparse Vector?

A Sparse vector is a type of local vector which is represented by an index array and a value array.

public class SparseVector

extends Object

implements Vector

Example: sparse1 = SparseVector(4, [1, 3], [3.0, 4.0])

where:

4 is the size of the vector

[1,3] are the ordered indices of the vector

[3,4] are the value

33. Describe how model creation works with MLlib and how the model is applied.

MLlib has 2 components:

Transformer: A transformer reads a DataFrame and returns a new DataFrame with a specific transformation applied.

Estimator: An estimator is a machine learning algorithm that takes a DataFrame to train a model and returns the model as a transformer.

Spark MLlib lets you combine multiple transformations into a pipeline to apply complex data transformations.

The following image shows such a pipeline for training a model:

The model produced can then be applied to live data:

34. What are the functions of Spark SQL?

Spark SQL is Apache Spark’s module for working with structured data.

Spark SQL loads the data from a variety of structured data sources.

It queries data using SQL statements, both inside a Spark program and from external tools that connect to Spark SQL through standard database connectors (JDBC/ODBC).

It provides a rich integration between SQL and regular Python/Java/Scala code, including the ability to join RDDs and SQL tables and expose custom functions in SQL.

35. How can you connect Hive to Spark SQL?

To connect Hive to Spark SQL, place the hive-site.xml file in the conf directory of Spark.

Using the Spark Session object, you can construct a DataFrame.

result=spark.sql(“select * from <hive_table>”)

36. What is the role of Catalyst Optimizer in Spark SQL?

Catalyst optimizer leverages advanced programming language features (such as Scala’s pattern matching and quasi quotes) in a novel way to build an extensible query optimizer.

37. How can you manipulate structured data using domain-specific language in Spark SQL?

Structured data can be manipulated using domain-Specific language as follows:

Suppose there is a DataFrame with the following information:

val df = spark.read.json("examples/src/main/resources/people.json")

// Displays the content of the DataFrame to stdout

df.show()

// +----+-------+

// | age|   name|

// +----+-------+

// |null|Michael|

// |  30|   Andy|

// |  19| Justin|

// +----+-------+

// Select only the "name" column

df.select("name").show()

// +-------+

// |   name|

// +-------+

// |Michael|

// |   Andy|

// | Justin|

// +-------+

// Select everybody, but increment the age by 1

df.select($"name", $"age" + 1).show()

// +-------+---------+

// |   name|(age + 1)|

// +-------+---------+

// |Michael|     null|

// |   Andy|       31|

// | Justin|       20|

// +-------+---------+

// Select people older than 21

df.filter($"age" > 21).show()

// +---+----+

// |age|name|

// +---+----+

// | 30|Andy|

// +---+----+

// Count people by age

df.groupBy("age").count().show()

// +----+-----+

// | age|count|

// +----+-----+

// |  19|    1|

// |null|    1|

// |  30|    1|

// +----+-----+

38. What are the different types of operators provided by the Apache GraphX library?

Property Operator: Property operators modify the vertex or edge properties using a user-defined map function and produce a new graph.

Structural Operator: Structure operators operate on the structure of an input graph and produce a new graph.

Join Operator: Join operators add data to graphs and generate new graphs.

39. What are the analytic algorithms provided in Apache Spark GraphX?

GraphX is Apache Spark's API for graphs and graph-parallel computation. GraphX includes a set of graph algorithms to simplify analytics tasks. The algorithms are contained in the org.apache.spark.graphx.lib package and can be accessed directly as methods on Graph via GraphOps. 

PageRank: PageRank is a graph parallel computation that measures the importance of each vertex in a graph. Example: You can run PageRank to evaluate what the most important pages in Wikipedia are.

Connected Components: The connected components algorithm labels each connected component of the graph with the ID of its lowest-numbered vertex. For example, in a social network, connected components can approximate clusters.

Triangle Counting: A vertex is part of a triangle when it has two adjacent vertices with an edge between them. GraphX implements a triangle counting algorithm in the TriangleCount object that determines the number of triangles passing through each vertex, providing a measure of clustering.

40. What is the PageRank algorithm in Apache Spark GraphX?

PageRank measures the importance of each vertex in a graph, assuming an edge from u to v represents an endorsement of v’s importance by u.

If a Twitter user is followed by many other users, that handle will be ranked high.

PageRank algorithm was originally developed by Larry Page and Sergey Brin to rank websites for Google. It can be applied to measure the influence of vertices in any network graph. PageRank works by counting the number and quality of links to a page to determine a rough estimate of how important the website is. The assumption is that more important websites are likely to receive more links from other websites.

A typical example of using Scala's functional programming with Apache Spark RDDs to iteratively compute Page Ranks is shown below:

Conclusion

Take our Apache Spark and Scala Certification Training, and you’ll have nothing to fear. It’s a wonderful course that’ll give you another superb certificate. In it, you’ll advance your expertise working with the Big Data Hadoop Ecosystem. Also, you’ll master essential skills of the Apache Spark open-source framework and the Scala programming language, including Spark Streaming, Spark SQL, machine learning programming, GraphX programming, and Shell Scripting Spark. You’ll also understand the limitations of MapReduce and the role of Spark in overcoming these limitations and learn Structured Query Language (SQL) using SparkSQL, among other highly valuable skills that will make answering any Apache Spark interview questions a potential employer throws your way.