Top Redis Interview Questions: Prepare for Your Job Interview most asked Questions for freshers

Top Redis Interview Questions : Redis is an open-source, in-memory NoSQL key-value data store that is mostly utilized as a quick-response database or application cache. Instead of storing data on a disk or solid-state drive (SSD), it keeps data in memory, which contributes to its unmatched performance, speed, and dependability.

A database administrator or software engineer with expertise in Redis database design, implementation, and upkeep is known as a Redis developer. It is their responsibility to maximize the scalability, stability, and performance of applications by utilizing Redis’s features.

Here are some Top Redis Interview Questions: Prepare for Your Job Interview most asked Questions for freshers

1.Explain the Replication Features of Redis?

Redis has strong replication capabilities to guarantee redundancy in data and high availability. Establishing a master-slave relationship between several Redis instances is necessary for replication. All write operations and changes are handled by the master instance, and data consistency is maintained throughout the cluster by the slave instances replicating the master’s data.

Redis provides two primary replication modes:

• Snapshotting: Every so often, the master takes a photo of the whole dataset and delivers it to the slave. After loading the snapshot, the slave keeps getting updates from the master.
• Append-Only File (AOF): Every write operation is appended to a log file by the master. The commands to duplicate the data are carried out by the slave by tailing the log file. Because AOF logs every change, it offers greater consistency and durability than snapshotting.

2. what is difference between Memcached and Redis?

Memcached : An open-source distributed memory object caching system in memory is called Memcached. By caching frequently accessed data, it is mostly used to enhance the performance of dynamic online applications. Data is stored in Memcached as key-value pairs, where retrieving the matching value requires the key. It’s a great option for caching basic data structures because of its speed and simplicity of construction.

Redis : Another open-source, in-memory data structure storage is called Redis. Redis has a far more feature-rich feature set than Memcached, even though it may also be used for caching. Numerous data structures are supported by it, such as lists, strings, hashes, sets, sorted sets, and more. Redis’s adaptability makes it appropriate for a greater variety of use cases, including message queuing, session management, and real-time analytics. In addition, Redis offers capabilities like replication, clustering, and durability, which makes it a more reliable and scalable option than Memcached.

3. Which are the different data types used in Redis?

Redis supports a variety of data types, each with its own unique characteristics and use cases:

• Strings : Simple text strings are stored in this most fundamental sort of data.
• Hashes : allows you to store several key-value pairs inside of a single hash. It represents a key-value map.
• Lists : items can be added or removed from either end of an ordered collection of items.
• Sets: Unordered sets of distinct elements that are employed in union, intersection, and difference operations.
• Sorted Sets: Perfect for range-based queries, priority queues, and leaderboard implementation.

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4.How can you enhance the durability of Redis?

Redis provides various techniques to improve its resilience, guaranteeing data persistence even in the case of unplanned system failures or shutdowns:

1.Persistence:

This write-ahead log keeps track of every command that is run on the server. It can be set to write to disk every N seconds or after M modifications. By default, it writes to disk on a regular basis. Although AOF is quite durable, it might not function as well as RDB.
This is a disk-saved snapshot of the complete dataset. It is set up to save the dataset after a predetermined amount of modifications or after a predetermined amount of time. Although RDB is typically faster than AOF, it is less durable since it can lose some data in the event of a crash that occurs in between saves.

2. Replication:

You can use this to make several read copies of your main Redis instance. Data availability can be ensured by promoting one of the replicas to become the new primary in the event that the original instance fails. Depending on the trade-offs you want to make between consistency and performance, replication can be set up to use either an asynchronous or synchronous mode.

3.Clustering:

This splits the dataset across several nodes, allowing you to scale Redis horizontally. It guarantees high availability and scalability by offering automatic failover and rebalancing. Redis Cluster provides higher performance and flexibility for large-scale applications, but it requires a more complicated setup than replication.

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5. What is the difference between Redis and RDBMS?

• While RDBMS is a SQL database, Redis is a NoSQL database.
• RDBMS adheres to the table structure, whereas Redis follows the key-value structure.
  RDBMS is quite slow, however Redis is really quick.
• Whereas RDBMS keeps its dataset in secondary memory, Redis stores all of its dataset in primary memory.
• RDBMS is used to store large files, but Redis is typically used to store small, frequently accessed files.
• Only official support for Linux, BSD, Mac OS X, and Solaris is offered by Redis. Currently, it does not offer official support for Windows, whereas RDBMS does.

6. What is in-memory Database?

Databases that keep all of their data in the main memory (RAM) of a computer rather than on a disk are known as in-memory databases. When compared to conventional disk-based databases, this considerably accelerates data access, which makes them perfect for applications requiring incredibly quick read and write operations.

With in-memory databases, the laborious process of retrieving data from a slower storage medium is eliminated, in contrast to typical databases that retrieve data from disk drives. They are therefore well suited for high-performance computing, real-time analytics, and other applications where speed is crucial because of their significantly reduced latency and increased throughput. Nevertheless, compared to disk-based databases, in-memory databases sometimes have less storage space, and their data is susceptible to loss in the event of a system failure or power outage.

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7. Explain Blocking operations on lists.

Building message queues and other asynchronous communication patterns in Redis requires blocking operations on lists. With the use of these procedures, clients can hold off on connecting until the predetermined condition is satisfied as they wait for components in a list to become accessible.

BLPOP is among the most often used blocking operations. With this command, the first element in a list’s head is removed and returned. The command will close the connection if the list is empty and wait for a new element to be added or until the timeout is reached. Because of this, it’s perfect for using message queues, in which senders can post messages to a list and recipients can pause until a message becomes available.

BRPOP is another blocking operation that functions on the tail of the list rather than the head of the list. It is similar to BLPOP. When implementing stacks or last-in-first-out (LIFO) queues, this can be helpful.

8.Explain SUNIONSTORE & SINTERSTORE.

SUNIONSTORE and SINTERSTORE are two Redis commands used to perform set operations and store the results in a new set.

SUNIONSTORE : computes and saves the result of the union of many sets in a new set. This indicates that it creates a single set by combining every distinctive element from the provided sets. For instance, SUNIONSTORE would generate a new set with the components {1, 2, 3, 4, 5} if you had two sets, A and B, with A = {1, 2, 3} and B = {3, 4, 5}.

SINTERSTORE : computes and saves the intersection of many sets, creating a new set with the result. This indicates that it identifies the components shared by each of the supplied sets. Given that {3} is the lone element shared by sets A and B, SINTERSTORE would produce a new set containing {3} using the same example as before.

9. Explain REPL and Redis-CLI.

REPL (Read-Eval-Print Loop) : is an interactive computing environment that allows you to enter commands, execute them, and see the results immediately. In the context of Redis, REPL is a built-in feature of the Redis CLI that provides a convenient way to interact with a Redis server. You can type Redis commands directly into the REPL, and the results will be displayed on the screen. This makes it easy to test commands, experiment with different data structures, and troubleshoot issues.

Redis-CLI : Redis’s command-line interface is called Redis-CLI. It offers a method for using the terminal or command prompt to communicate with a Redis server. Redis-CLI provides additional functionality including batching commands, running scripts, and moving RDB files in addition to the REPL. It is a flexible tool that may be applied to a range of activities, from straightforward administration to intricate testing.

10. What is meant by ZSET in Redis?

In Redis, an ordered set of unique elements is stored in a data structure called a ZSET (sorted set). Every element has a score, and the elements are arranged according to their scores. Because of this, ZSETs are perfect for using in range searches, leaderboards, and other applications where items need to be arranged according to a numerical value.

ZSETs preserve an unordered order according to the element scores, in contrast to ordinary sets. This makes it possible for you to quickly obtain items that fall into a particular range, like the top 10 scores or elements with scores between 50 and 100. ZSETs may also be used to create priority queues, in which items with higher scores are handled first.

11.What is meant by data modeling in Redis?

Designing the organization of your data within the database to maximize effectiveness and performance is known as data modeling in Redis. Redis provides a more flexible approach than relational databases, which rely on tables and schemas. You can select from a variety of data structures depending on your particular requirements.

Knowing the connections between your data and choosing the right data structures are essential to efficient Redis data modeling. For instance, strings or hashes can be used to hold key-value pairs. Lists or sorted sets can be used to hold ordered collections. You may build an effective and scalable data model by carefully examining your use case and the features of each data structure.

12.How to understand Redis transaction?

Redis transactions are a way to execute several commands as a single atomic unit by grouping them together. This indicates that a transaction’s commands can either all be successfully executed or none at all. This is very helpful in preventing race-based situations and guaranteeing data consistency.

Understanding the MULTI, EXEC, and DISCARD commands is essential to comprehending Redis transactions. By starting a transaction, the MULTI command enables you to queue numerous commands. All of the queued commands are carried out in one atomic operation by the EXEC command. The transaction is terminated and the database is left unaltered if any of the commands are unsuccessful. All pending commands are discarded by the DISCARD command without being executed.

Data integrity and inconsistency can be prevented and complicated operations can be assured to be conducted as a single unit by using transactions.

13.How many keys can a Redis instance store at most?

Redis does not enforce a cap on the quantity of keys it can hold. Your system’s available RAM is the main constraint. The number of keys you can store depends on the size of your keys and values as well as the total RAM allotted to Redis. This is because each key and its corresponding value take up memory.

Redis has been shown to be able to manage hundreds of millions of keys per instance in practice. However, because hash table conflicts and greater memory utilization occur when the number of keys increases, you can notice a decline in performance. You can use numerous instances or clusters to scale your Redis deployment horizontally in order to handle this.

14.What is the use of MGET in Redis?

Using the Redis command MGET, you can quickly and effectively obtain several values linked to several keys in a single action. Performance can be greatly increased by doing this as opposed to running separate GET commands for every key.

You may decrease the amount of network round trips and boost your application’s overall performance by utilizing MGET. When you need to retrieve data for several keys at once, like when generating a web page or handling a large number of queries, this is quite helpful.

15.How to create a new database in Redis?

Databases are not expressly created by Redis. Rather, it segregates distinct datasets within a single Redis instance using the notion of “databases”. There can be up to 16 databases (numbered 0 through 15) in each Redis instance.

16. Explain the concept of Redis eviction policies and why they are used.

When your data set grows larger than the predefined maximum memory limit, Redis eviction procedures take effect. These policies basically decide which data should be deleted to create place for new information. Various techniques are available, such as Least Recently Used (LRU) that removes the keys that haven’t been accessed in the longest, and Least Frequently Used (LFU) that targets the keys that are accessed the least. In an effort to reduce the impact on performance, this helps free up space.

The allkeys-random policy is another popular one that arbitrarily chooses any key to evict. Additionally, there is a volatile-lru policy that employs the LRU algorithm to only evict keys that have an expiration specified. These policies are essential for programs that have memory limits because they keep the system from crashing due to memory exhaustion and assist sustain performance.

17.How would you secure a Redis instance in a production environment?

To begin, set Redis to listen only on localhost or provide an interface to bind to. Limit which IP addresses are allowed to access the Redis port, which is normally 6379, by using a firewall. Redis AUTH can be enabled by creating a strong password.

Another best practice is to set up a rename-command directive in the configuration file to disable any unnecessary commands. Redis can also be further isolated from other system components by running it inside a virtual machine or container with restricted access, which adds an extra degree of security.

18.What is the process of setting environment variables for a Redis client and server?

For Redis client and server computers, you can set environment variables by right-clicking, selecting Properties from the menu, choosing Advanced settings, clicking Path variables under System Variable Path, and creating a new environment variable for the Redis folder containing the CLI files and server executable.