20 Delta Lake Interview Questions and Answers

Delta Lake is a open-source storage layer that sits on top of your existing data storage infrastructure and enables ACID transactions, versioning, and schema enforcement for your data. Delta Lake is an important tool for data engineers and data scientists who want to make their data processing pipelines more reliable and efficient. In this article, we review some commonly asked Delta Lake interview questions and provide guidance on how to answer them.

Delta Lake Interview Questions and Answers

Here are 20 commonly asked Delta Lake interview questions and answers to prepare you for your interview:

1. What is Delta Lake?

Delta Lake is a storage layer that brings ACID (atomicity, consistency, isolation, and durability) transactions to Apache Spark and big data workloads. Delta Lake provides a number of benefits including the ability to manage large amounts of data, the ability to provide data consistency across multiple Spark sessions, and the ability to easily rollback changes.

2. How does Delta Lake relate to Apache Spark?

Delta Lake is built on top of Apache Spark and provides a way to manage storage and improve performance for Spark applications. Delta Lake uses a columnar format and stores data in Parquet files, which helps to improve performance when Spark is reading and writing data. Delta Lake also provides a way to manage transactions and keep track of changes to data, which can be helpful in ensuring data consistency.

3. Can you explain what a Delta Table is in the context of Delta Lake?

A Delta Table is a table that is stored in the Delta Lake format. Delta Lake is a transactional storage layer that sits on top of your data lake and provides ACID transactions, data versioning, and schema enforcement. Delta Tables are stored as Parquet files in S3 and can be queried using SQL.

4. Why should I use Delta Lake instead of storing data in Parquet format on S3 or HDFS?

Delta Lake offers a number of advantages over storing data in Parquet format on S3 or HDFS. Delta Lake is designed to provide ACID transactions, which means that your data will be safe from corruption even if there are power outages or other failures. Delta Lake also offers scalability and performance advantages over Parquet, making it a good choice for large-scale data processing.

5. What are some common problems that Delta Lake solves for us?

Delta Lake is a great tool for managing data in a cloud environment. It helps us to keep track of changes to data over time, and it also allows us to easily share data between different users and applications. Delta Lake also provides a way to automate the process of data management, which can save us a lot of time and effort.

6. Can you name some technologies that Delta Lake can integrate with and why it’s useful to do so?

Delta Lake can integrate with a variety of technologies, including Apache Spark, Apache Hive, and Apache Kafka. This is useful because it allows for a more seamless data processing experience, as data can be easily read from and written to Delta Lake regardless of the technology being used.

7. What are some important features of Delta Lake?

Delta Lake is a transactional storage layer that sits on top of your data lake and enables you to do things like:

– Read, write, and manage data in your data lake
– Perform ACID transactions
– Make your data lake “lakehouse ready”

Some key features of Delta Lake include:

– Optimistic concurrency control
– Time travel
– Data versioning
– Unification of batch and streaming data

8. What does DML mean in the context of Delta Lake?

DML stands for Data Manipulation Language. In the context of Delta Lake, it refers to the various SQL commands that can be used to manipulate data stored in a Delta table. This includes commands for inserting, updating, and deleting data.

9. What is ACID? Is Delta Lake ACID compliant? If yes, how?

ACID stands for Atomic, Consistent, Isolation, and Durability. Delta Lake is ACID compliant because it supports atomic transactions, which means that all changes to the data in a Delta table are either all committed, or all rolled back. Delta Lake also supports consistent reads, meaning that readers will always see the data as it was at the time the transaction was started. Finally, Delta Lake supports isolation through its time travel feature, which allows users to view data as it existed at any point in time.

10. What are the main components of a Delta Lake?

The main components of a Delta Lake are the Delta table, the Delta log, and the Delta cache. The Delta table is the central data store that contains all of the data for a Delta Lake. The Delta log is a transaction log that tracks all of the changes that have been made to the Delta table. The Delta cache is a columnar cache that stores the most recent version of the data in the Delta table.

11. What is Open Source Delta Lake? What are some major differences between open source and commercial versions of Delta Lake?

Open source Delta Lake is a project that aims to provide a free and open-source implementation of the Delta Lake platform. The major difference between the open source and commercial versions of Delta Lake is that the open source version is not as feature-rich as the commercial version. The commercial version includes additional features such as a web-based user interface, support for multiple languages, and integration with other data platforms.

12. What is the best way to create Delta Tables?

The best way to create Delta Tables is to use the Delta Lake format. This format allows for easy creation of Delta Tables, as well as easy management and manipulation of the data inside of them.

13. When using Delta Lake, how do we perform upserts?

Delta Lake supports two types of upserts:

1. Merge: The MERGE command allows you to update or insert data into a Delta table based on a given condition. The condition is specified using a WHERE clause. If the condition evaluates to true, the UPDATE action is performed; if the condition evaluates to false, the INSERT action is performed.

2. Insert: The INSERT INTO command can be used to insert data into a Delta table. This command will insert new rows into the table, but will not update existing rows.

14. What is the difference between append and overwrite operations when working with Delta Tables?

Append operations simply add new data to the end of an existing Delta table, while overwrite operations will completely replace the data in a Delta table with new data.

15. How do we manage schema changes in Delta Lake?

Delta Lake uses a schema enforcement mechanism to ensure that data is always written in the correct format. This means that when a schema change is made, any data that does not conform to the new schema is automatically rejected. This ensures that data is always consistent and that there are no issues with compatibility.

16. What is time travel? How do we enable it when using Delta Lake?

Time travel is a feature of Delta Lake that allows users to access and query data as it existed at any point in time. This is accomplished by creating a time-stamped version of each file as it is written to the Delta table. To enable time travel, users simply specify a timestamp when they query the table.

17. What is an index in the context of Delta Lake?

An index is a data structure that helps Delta Lake optimize query performance by allowing quick lookups of data. An index on a Delta table can be used to speed up queries that filter on a particular column or columns.

18. What are checkpoints and snapshots?

Checkpoints are a method of storing data that allows for easy recovery in the event of a failure, while snapshots are a method of storing data that allows for easy rollback to a previous version.

19. What is the process used by Delta Lake to load data into a table from another file system?

Delta Lake uses a process called “upserts” to load data into a table from another file system. This process first checks to see if a row with the same primary key already exists in the table. If it does, then the row is updated with the new data. If the row does not exist, then it is inserted into the table.

20. What are the different modes available to read data from a Delta Lake table?

There are two modes available to read data from a Delta Lake table:

1. The first mode is called “full scan mode” and will read the entire contents of the table.
2. The second mode is called “incremental scan mode” and will only read data that has been added or changed since the last time the table was read.