Top 30 Apache Flink Interview Questions with Answers

1. What is Apache Flink?

Ans:- Apache Flink is an open-source stream processing framework that can also be used for batch processing. It is designed to be scalable, fault-tolerant, and efficient. Flink can be used to process unbounded and bounded streams, and it supports a variety of data sources and sinks.

2. What are the key features of Apache Flink?

Ans:- Some of the key features of Apache Flink include:

• Scalability: Flink can be scaled to handle large amounts of data.
• Fault tolerance: Flink is fault-tolerant and can recover from failures.
• Efficiency: Flink is designed to be efficient, both in terms of memory and CPU usage.
• Stateful processing: Flink can maintain state across multiple events, which makes it suitable for complex streaming applications.
• Windowing: Flink supports a variety of windowing techniques, which allow you to process data over a sliding time window.
• SQL support: Flink supports SQL, which makes it easy to integrate with existing data warehouses and BI tools.

3. What are the different types of streams in Apache Flink?

Ans:- There are two types of streams in Apache Flink: unbounded streams and bounded streams.

Unbounded streams are streams of data that have no defined end. Examples of unbounded streams include sensor data, social media data, and financial market data.
Bounded streams are streams of data that have a defined end. Examples of bounded streams include log files and transactional data.

4. What is the difference between Apache Flink and Apache Spark?

Ans:- Apache Flink and Apache Spark are both popular stream-processing frameworks. However, there are some key differences between the two frameworks:

• Flink is designed for both streaming and batch processing, while Spark is primarily designed for batch processing.
• Flink is more fault-tolerant than Spark.
• Flink is more efficient than Spark for streaming applications.
• Flink supports a wider variety of data sources and sinks than Spark.

5. What are the different execution modes of Apache Flink?

Ans:- Apache Flink has two execution modes:

• Local mode: This mode is used for development and testing. It runs the Flink application on a single machine.
• Cluster mode: This mode is used for production deployments. It runs the Flink application on a cluster of machines.

6. What are the different APIs in Apache Flink?

Ans:- Apache Flink provides three APIs:

DataStream API: This API is used for processing unbounded streams.
DataSet API: This API is used for processing bounded streams.
Table API: This API is used for processing structured data.

7. What are the different windowing techniques in Apache Flink?

Ans:- Apache Flink supports a variety of windowing techniques, including:

• Tumbling windows: These windows are fixed in size and slide across the stream.
• Sliding windows: These windows are variable in size and slide across the stream.
• Session windows: These windows are based on the arrival time of events.
• Count windows: These windows are based on the number of events that arrive within a given time interval.

8. What is the difference between event time and processing time in Apache Flink?

Ans:-

• Event time: This is the time at which an event occurs.
• Processing time: This is the time at which an event is processed by Flink.
• Flink allows you to choose between event time and processing time. Event time is typically used for applications that require accurate timestamps, such as fraud detection. Processing time is typically used for applications that do not require accurate timestamps, such as clickstream analysis.

9. What is the state of the art in Apache Flink?

Ans:- The state of the art in Apache Flink is constantly evolving. However, some of the latest features and improvements in Flink include:

• Support for Apache Kafka: This allows Flink to be used to process data from Kafka topics.
• Support for Apache Hadoop: This allows Flink to be used to process data from Hadoop Distributed File System (HDFS).
• Support for Apache Hive: This allows Flink to be used to query data from Hive tables.
• Support for Apache Storm: This allows Flink to be used to migrate Storm topologies.
• Support for Machine Learning: This allows Flink to be used to build machine learning models.

10. What are the challenges in Apache Flink?

Ans:- Some of the challenges in Apache Flink include:

• The learning curve can be steep.
• The documentation can be incomplete.
• The performance can be poo

11. What are Flink connectors, and why are they important?

Ans:- Flink connectors are libraries or modules that enable Flink to connect with external data sources and sinks. They are important for ingesting data into Flink and writing results to external systems.

12. What is the role of the Flink Task Manager?

Ans:- The Task Manager in Apache Flink is responsible for executing the tasks of a Flink job. It manages the actual execution of user-defined functions and stores the intermediate state.

13. What is the Flink DataSet API used for?

Ans:- The Flink DataSet API is used for batch processing and is designed for processing large volumes of data in a batch fashion.

14. How can you optimize the performance of a Flink application?

Ans:- Performance optimization in Flink can be achieved through various techniques such as tuning parallelism, configuring memory settings, optimizing state management, and choosing appropriate windowing strategies.

15. What is the role of the Flink CEP (Complex Event Processing) library?

Ans:- The Flink CEP library allows you to perform complex event pattern matching on event streams. It is useful for detecting sequences of events within a stream.

16. How does Flink handle late-arriving data in event time processing?

Ans:- Flink allows you to specify how late events should be handled using event time processing. You can define a windowing strategy to include late data or discard it, based on your application requirements.

17. What is Flink’s support for exactly-once processing semantics?

Ans:- Flink offers exact-once processing semantics through features like checkpointing, state management, and transactional sinks. This ensures that data is processed without duplication or loss.

18. What are Flink’s Table Sources and Sinks?

Ans:- Flink Table Sources are connectors to read data from external sources, and Table Sinks are connectors to write data to external sinks. They allow seamless integration of Flink with various data formats and systems.

19. What is a stateful operator in Apache Flink?

Ans:- A stateful operator in Flink is an operator that maintains state information across multiple input elements. It can store and update the state as data is processed.

20. How can you achieve exactly once stateful processing in Apache Flink?

Ans:- Exactly-once stateful processing can be achieved in Flink by enabling checkpointing and using stateful operators that support exactly-once semantics.

21. What file systems does Apache Spark support?

Ans:- Apache Spark is a powerful distributed data processing engine that processes data coming from multiple data sources. The file systems that Apache Spark supports are:

Hadoop Distributed File System (HDFS)

• Local file system
• Amazon S3
• HBase
• Cassandra, etc.

22. What is a Directed Acyclic Graph in Spark?

Ans: A directed Acyclic Graph or DAG is an arrangement of edges and vertices. As the name implies the graph is not cyclic. In this graph, the vertices represent RDDs, and the edges represent the operations applied to RDDs. This graph is unidirectional, which means it has only one flow. DAG is a scheduling layer that implements stage-oriented scheduling and converts a plan for logical execution to a physical execution plan.

23. What are deploy modes in Apache Spark?

Ans:- There are only two deploy modes in Apache Spark, client mode and cluster mode. The behavior of Apache Spark jobs depends on the driver component. If the driver component of Apache Spark will run on the machine from which the job is submitted, then it is the client mode. If the driver component of Apache Spark will run on Spark clusters and not on the local machine from which the job is submitted, then it is the cluster mode.

24. Roles of receivers in Apache Spark Streaming?

Ans:- Within Apache Spark Streaming Receivers are special objects whose only goal is to consume data from different data sources and then move it to Spark. You can create receiver objects by streaming contexts as long-running tasks on various executors. There are two types of receivers. They are Reliable receivers: This receiver acknowledges data sources when data is received and replicated successfully in Apache Spark Storage. Unreliable receiver: These receivers do not acknowledge data sources even when they receive or replicate in Apache Spark Storage.

25. What is YARN?

Ans:- Similar to Hadoop, YARN is one of the key features in Spark, providing a central and resource management platform to deliver scalable operations across the cluster. Running Spark on YARN needs a binary distribution of Spark that is built on YARN support.

26. List the functions of Spark SQL.

Ans:- Spark SQL is capable of:

• Loading data from a variety of structured sources
• Querying data using SQL statements, both inside a Spark program and from external tools that connect to Spark SQL through standard database connectors (JDBC/ODBC), e.g., using Business Intelligence tools like Tableau
• Providing rich integration between SQL and the regular Python/Java/Scala code, including the ability to join RDDs and SQL tables, expose custom functions in SQL, and more.

27. What are the benefits of Spark over MapReduce?

Ans:- Due to the availability of in-memory processing, Spark implements data processing 10–100x faster than Hadoop MapReduce. MapReduce, on the other hand, makes use of persistence storage for any of the data processing tasks.
Unlike Hadoop, Spark provides in-built libraries to perform multiple tasks using batch processing, steaming, Machine Learning, and interactive SQL queries. However, Hadoop only supports batch processing.
Hadoop is highly disk-dependent, whereas Spark promotes caching and in-memory data storage.
Spark is capable of performing computations multiple times on the same dataset, which is called iterative computation. Whereas, there is no iterative computing implemented by Hadoop.

28. Is there any benefit of learning MapReduce?

Ans:- Yes, MapReduce is a paradigm used by many Big Data tools, including Apache Spark. It becomes extremely relevant to use MapReduce when data grows bigger and bigger. Most tools like Pig and Hive convert their queries into MapReduce phases to optimize them better.

29. What is a Spark Executor?

Ans:- When SparkContext connects to Cluster Manager, it acquires an executor on the nodes in the cluster. Executors are Spark processes that run computations and store data on worker nodes. The final tasks by SparkContext are transferred to executors for their execution.

30. Name the types of Cluster Managers in Spark.

Ans:- The Spark framework supports three major types of Cluster Managers.

Standalone: A basic Cluster Manager to set up a cluster
Apache Mesos: A generalized/commonly-used Cluster Manager, running Hadoop MapReduce and other applications
YARN: A Cluster Manager responsible for resource management in Hadoop