Redis interview questions

Redis interview questions

An Overview of Redis

Redis stands for the REmote DIctionary Server. Redis is a BSD (Berkeley Software Distribution) licensed open-source key-value store. The Redis store uses data structures to store the data. This store is written in the C language, and it runs on the Portable Operating System Interfaces like Linux, Mac OS. Redis is used by programmers to develop a useful web application. Redis interview questions we are mentioning below will help you to gain enough of the knowledge about Redis.


  • Redis is very very fast as the data is stored in the memory
  • In Redis, there is no need for defining the tables. Therefore, it is flexible and straightforward.
  • Redis can be used with the existing database.
  • Redis has a rich set of data types

Redis is the fastest key-value store because it keeps the data in the RAM and that is why Redis is said to be an in-memory database. Redis is being used by Flickr, Twitter, StackOverflow, GitHub, Pinterest. All your questions related to Redis will be answered in the Redis interview questions mentioned below.

Development History

Redis was developed by Salvatore Sanfilippo. The first release of Redis was on 10th May 2009.

Latest Version:

Redis 5.0.3 is the newest version of Redis which got released on 12th December 2018.

Last update: 30 Nov 2019, 15 QuestionsAsk Question

Best Redis interview questions And Answers

Redis stands for REmote DIctionary Server. Redis is an open-source in-memory database which stores the data in the key-value pairs.

For example:- NAME = Ram, here NAME is the key and Ram is the value. In-memory database means that the data is stored in the memory, but the data can also be stored in the disk.

Benefits of Redis
  • in-memory database, therefore, it is swift.
  • Uses the data structure to store the data
  • Supports data replication
  • Can be used as a cache system as well as the database.
  • Data read, and Data write done by commands
  • Redis is simple to configure, learn and implement.
  • Redis allows data replication
  • Redis works on the Client-Server mechanism.
  • In Redis, there is no requirement of tables, rows, and columns.
  • Redis includes pipelining that means multiple commands can be clustered and send them at once.
  • Redis can be used as a database
  • Redis has the master-slave feature

The latest version of Redis is 5.0.3 which got released on 12th December 2018.

Redis can be installed on the Ubuntu machines by using the command:-

sudo apt-get install Redis-server

If the user wants Redis to be installed as an object cache for Wordpress or any other PHP, then the following command can be used:-

sudo apt-get install php-redis

If the user wants to configure the Redis as a cache, /etc/Redis/redis.conf file needs to be updated, and the text editor nano can be used for this purpose.

sudo nano /etc/redis/redis.conf

Any text editor can be used.

Here is one of the way of installing the Redis on Windows:-


1.Install some packages


  • $ sudo apt-get install build-essential
  • $ sudo apt-get install tcl8.5

2. Download the source code of the latest version of Redis.

  • http://download.redis.io/releases/redis-5.0.3.tar.gz

3. Extract the file that has been downloaded.


4.Compile the Redis source

  • $ sudo make distclean
  • $ sudo make –j


5.Test the compiled files ((optional))

  • $ sudo make test -j


6. After compilation, copy the Redis binaries under /usr/local/bin/ and then install the Redis server by the following instructions:-

  • $ sudo make install -j
  • $ cd utils
  • $ sudo ./install_server.sh

7. Installation Completed


Point to be noted:- Go through this Q&A very thoroughly as this is one of the vital Redis interview questions.

S.no Redis Memcached
1. Supports data replication Does not support data replication
2. Single threaded Architecture Multithreaded Architecture
3. Many data types can be used Limited to strings data type
  • DEL:-if the key exists then it deletes the key

              Syntax:- redis> DEL KEY_NAME

  • EXISTS:-this checks whether the key exists or not

              Syntax:- redis> EXISTS KEY_NAME

  • EXPIRE:- this sets the expiry date of the key after the specified time

              Syntax:- redis> Expire KEY_NAME TIME_IN_SECONDS

  • TTL:-this shows the time remaining in the keys expiry
  • RANDOMKEY:-this returns the random key

              Syntax:- redis> RANDOMKEY

  • TYPE:-this return the data type of the value which is stored in the key
  • KEYS pattern:- this return the keys which match with the mentioned pattern
S.no Redis MongoDB
1. Key-Value store Document type of store
2. The language used is C The language used is C++
3. Speed is Fast Speed is slow
4. Server-side script is Lua Server-side script is Javascript

Following are the Redis data types:-

1. Strings:-

2. Hashes:- They represent the objects.

3. Lists:-they are the set of lines that are sorted according to the insertion order Syntax:-

4. Sets:- It is a collection of the string arranged randomly

5. Sorted Sets:-similar like the sets but here with each member, there is a score which may get repeated while the members will be unique


This particular Redis interview question explains Redis data types.

The following two commands can be used to empty the database.

  • FLUSHDB:- Removes all the data from the database which the user is currently using.

             Syntax:- redis-cli flushdb

  • FLUSHALL:- Removes the data from all the databases.

             Syntax:-redis-cli flushall

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