Top Redis Interview Questions and Answers

Q1. What is Redis?

Ans

Redis is a distributed in-memory key-value database, cache, and message broker with optional durability. Redis supports different kinds of abstract data structures, such as strings, lists, maps, sets, sorted sets, HyperLogLogs, bitmaps, streams, and spatial indexes.

Q2. What does Redis stands for?

Ans

Redis stands for REmote DIctionary Server.

Q3. List the main operation keys of Redis.

Ans

The main operation keys of Redis are given below-

• TTL key
  
• TYPE key
  
• EXISTS key
  
• EXPIRE key seconds
  
• DEL key
  
• EXPIREAT key timestamp

Q4. What is Redis Replication?

Ans

Redis uses non-blocking asynchronous replication, with asynchronous replica-to-master acknowledges of the amount of data processed. A master can have multiple replicas. It ensures that the master will continue to handle queries when one or more replicas perform the initial synchronization or a partial resynchronization. Replication is also largely non-blocking on the replica side.

Q5. How can Redis be started?

Ans

The given path can be followed to start Redis-

/etc/init.d/redis-server start

Q6. How can Redis be Re-started?

Ans

The given path can be followed to re-start Redis-

/etc/init.d/redis-server restart

Q7. How can Redis be stopped?

Ans

The given path can be followed to stop Redis-

/etc/init.d/redis-server stop

Q8. What is meant by "Redis is Binary Safe"?

Ans

Binary Safe represents having a known length, but no special character limits it. Any value can be stored by the user up to the given size. A string value can have a length of 512 MB.

Q9. List out all the data structures that are supported by Redis

Ans

Redis supports following Data Structures:

• Strings
• Hashes
• Lists
• Sets
• Sorted sets with range queries
• Bitmaps
• Hyperloglogs
• Geospatial indexes with radius queries

Q10. What are the limitations of Redis? 

Ans

• The whole dataset has to be kept in memory - so the space is limited
• Single threaded
• It has got limited client support for consistent hashing
• It has significant overhead for persistence
• It is not deployed widely

Q11. How we can use Redis with .Net application?

Ans

For use Redis in .net application need to follow given steps:

• Download Redis Server
• Install Redis Server
• Download Redis Client
• Set Configuration into Web.config File
• Use Redis Client Class

Q12. What are differences between Redis and RDBMS?

Ans

Q13. What is the maximum size of key (String) in redis?

Ans

According to the redis official docs, the maximum size of key in redis is 512MB.

Q14. How many data types are there in Redis?

 Ans

Redis provide 5 types of data types. Strings, Hashes, Lists, Sets, Sorted Sets.

Q15. What is Redis Replication?

Ans

Redis uses non-blocking asynchronous replication, with asynchronous replica-to-master acknowledges of the amount of data processed. A master can have multiple replicas. It ensures that the master will continue to handle queries when one or more replicas perform the initial synchronization or a partial resynchronization. Replication is also largely non-blocking on the replica side.

Q16. Explain the list operations available in Redis.

Ans

The list operations are given below-

• LPOP- An element is removed from the head by it.
• RPOP- An element is removed from the tail by it.
• LPUSH- A new element is inserted on the head by this operation.
• RPUSH- A new element is inserted on the head by this operation.
• LRANGE- An element is printed from the specified position

Q17. What is meant by ZSET in Redis?

Ans

ZSET means a Redis Sorted Set where we can document a Redis data type. Each key in the assorted set contains multiple values associated with a value score that is floating. Redis provides the unique feature of accessing it by a member such as a HASH. Also, we can access the items by the sorted order as well as the values of the scores.

Q18. How can the array data be obtained from Redis?

Ans

We can get the array data from Redis by using the given commands

$list = $redis ->lrange (“tutorials”, 0, 5);
print_r($list);
/*array ([0] => Mysql [1] => Mongodb [2] => Redis [3] => MySQL [4]=> PHP [5] => Mysql)*/

Q19.How can the running of Redis be checked?

Ans

try
{
$redis = new Redis();
$redis -> connect (‘127.0.0.1’, 6379);
echo “Redis is running.”;
echo “Server is running:”. $redis -> ping()
}
catch (Exception $e)
{
echo $e -> getMessage();
}

Q20. Are transactions supported by Redis?

Ans

EXEC, MULTI, WATCH, and DISCARD are the foundations of Redis transactions. A group of commands can be executed in a single step by these. And the following two important guarantees are there-

• All the commands are executed and serialized in a transaction sequentially. A request issued by some other client can never be served in the middle of the Redis transaction's execution. Single isolated execution of the commands is guaranteed by it.
• A Redis transaction is atomic; that is, either all or none of the commands are processed.

Q21. What are some of the languages supported by Redis?

Ans

The following languages are supported by Redis-

• C#
  
• C++
  
• C
• Python
  
• Java
  
• Erlang
  
• PHP
  
• Scala

Q22. How does Redis differ from most other databases?

Ans

Redis is an open-source, NoSQL, and in-memory data structure store. The principle of a key-value store is followed by Redis.

It is very persistent, fast, portable, and supports several languages like Java, Python, C, C++, R, Scala, Lua, JavaScript, Ruby, Rust, Tcl, Go, etc.

Q23. In which language is Redis written?

Ans

ANSI C is the language in which Redis is written. It is mostly used for session management and cache solution. And unique keys are created by it for store values.