Redis Interview Questions for Freshers/Redis Interview Questions and Answers for Freshers & Experienced

What is the master-slave replication model of the Redis cluster?

In order to make the cluster still available in the case where some nodes fail or most of the nodes cannot communicate, the cluster uses the master-slave replication model, and each node will have n-1 A duplicate.

Posted Date:- 2021-11-15 08:29:12

What is the advantages and disadvantages of JEDIS and Redisson?

JEDIS is the client of Redis's Java, and its API provides support for comparing the comprehensively redis command; Redisson implements distributed and scalable Java data structures, and Jedis phase
Comparison, functions are simpler, not supported by string operations, not supporting REDIS features such as sorting, transaction, pipeline, partitioning.

Redisson's aim is to promote the use of the user's attention to the focus of Redis, so that the user can more focus on the processing business logic.

Posted Date:- 2021-11-15 08:28:27

What is the case of the Redis cluster?

There is a cluster of the three nodes of A, B, and C. If there is no replication model, if the Node B failed, the entire cluster will be missing. 5501-11000 This range of slots are not available.

Posted Date:- 2021-11-15 08:27:32

How to delete all the cache using pRedis in php?

Redis is one of the powerful PHP Redis clients that enables the user to work with Redis in PHP. To delete all the cache using pRedis in PHP, use the following command.


This command is the Redis equivalent of FLUSHALL that deletes all the cache of the database connected to the Redis.

Posted Date:- 2021-11-15 07:29:05

What is use of MGET in Redis?

MGET is a command in Redis that returns the value of the key. You pass the name of the key along with the MGET command, and the value gets returned as an array. MGET returns nil for keys that don’t exist or keys that don’t have any value.

> MGET keyname
> SET key “keyValue”
> MGET key
1) “keyValue”

Posted Date:- 2021-11-15 07:28:01

Enlist major Redis commands?

Redis is mainly used by the system admins, and some of the major commands in Redis are,

* Redis-CLI – to connect to Redis.
* INFO – to get server statistics
* CONFIG GET * - to change runtime configuration
* SELECT “database number” - to select the database by its number
* FLUSHDB – to drop the currently selected database and its keys
* FLUSHALL – to drop all the database and its keys
* BGSAVE – to do a database backups
* CLIENT LIST – to list all the connections with the database
* MONITOR – to track all the network traffic

Posted Date:- 2021-11-15 07:21:00

Redis Other implementation of transaction

be based on Lua Script ,Redis It can ensure that the commands in the script are one-time 、 To execute in order ,

It also does not provide rollback of transaction running errors , If some commands run incorrectly during execution , The rest of the command will continue to run

Based on the middle marker variable , Another flag variable is used to identify whether the transaction is completed , When reading data, first read the tag variable to determine whether the transaction is completed . But this will require additional code implementation , More complicated

Posted Date:- 2021-11-15 07:19:13

How to empty a Redis Database?

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

Posted Date:- 2021-11-15 07:17:19

Please mention some operation keys of Redis?

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

Posted Date:- 2021-11-15 07:16:20

How to install Redis Ubuntu?

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.

Posted Date:- 2021-11-15 07:15:16

Redis How many databases are there by default db Action ?

Redis The default support 16 A database , Can be configured by databases To modify this number . The client and Redis After the connection is established, it will automatically select 0 The database , But it can be used at any time select Command to change database .

Redis Support for multiple databases , And each database is isolated and cannot be shared , And it's based on a single machine , If it's a cluster, there's no concept of a database .

Posted Date:- 2021-11-15 07:11:02

Why? redis You need to put all the data in memory ?

Redis In order to achieve the fastest read-write speed, read all data into memory , And write data to disk asynchronously . therefore redis It has the characteristics of fast and data persistence . If you don't put the data in memory , disk I/O Speed is a serious effect redis Performance of . Today, memory is getting cheaper ,redis Will be more and more popular .

Posted Date:- 2021-11-15 07:10:25

How we can use Redis With .net Application?

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

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

Posted Date:- 2021-11-15 07:04:56

Is using Redis together with an on-disk database a good idea?

Yes, a common design pattern involves taking very write-heavy small data in Redis (and data you need the Redis data structures to model your problem in an efficient way), and big blobs of data into an SQL or eventually consistent on-disk database. Similarly sometimes Redis is used in order to take in memory another copy of a subset of the same data stored in the on-disk database. This may look similar to caching, but actually is a more advanced model since normally the Redis dataset is updated together with the on-disk DB dataset, and not refreshed on cache misses.

Posted Date:- 2021-11-15 07:03:19

How Do I Move A Redis Database From One Server To Another?

* use BGSAVE command to Save a spanshot of the database into a dump.rdb.

* Copy this dump.rdb file into another server.

Posted Date:- 2021-11-15 07:02:44

Why Redis Is Different As Compared To Other Key-value Stores?

* Redis values can contain more complex data types, with atomic operations.
* Redis is an in-memory but persistent on disk database

Posted Date:- 2021-11-15 07:01:32

How can you use Redis with .Net application?

To use Redis in .Net applications, follow these steps:

* First, Download Redis Server.
* Install Redis Server.
* Download Redis Client.
* Set Configuration into Web.config File.
* Use Redis Client Class.

Posted Date:- 2021-11-15 07:00:18

How can you enhance the durability of Redis?

* Whenever a new command is added to the append log file, call Fsysnc() each time.

* Keep calling Fsysnc() in every second. Despite of the 1 second data lose in the case of system fails.

Posted Date:- 2021-11-15 06:59:14

We all know that Reds is fast, but is it also durable?

In Redis, there is always a trade-of between durability and speed. In the case of system failure, it may lose data which is not stored.

Posted Date:- 2021-11-15 06:58:36

How to empty a redis database?

FLUSHDB - clears active database
FLUSHALL - clears existing databases

Posted Date:- 2021-11-15 06:58:01

What is the difference between Redis and RocksDB?

* Redis is efficientbut non scable.
* Redis is all in -memory.
* RocksDB supports multi -threading library.
* RocksDB is in-memory but also uses flash storage.

Posted Date:- 2021-11-15 06:57:29

Mention what are the things you have to take care while using Redis?

While using Redis one must take care of

* Select a consistent method to name and prefix your keys. Manage your namespace.

* Create a “Registry” of key prefixes that maps each of your internal documents for that application which “own” them

* For every class you put through into your Redis infrastructure: design, implement and test the mechanisms for garbage collection or data migration to archival storage

* Design, implement and test a sharding library before you have invested much into your application deployment and make sure that you keep a registry of “shards “replicated on each server

* Separate all your K/V store and related operations into your own library/API or service

Posted Date:- 2021-11-15 06:56:33

Redis List data-type.

Internal Implementation: Linked-List
Redis Lists are simply lists of strings, sorted by insertion order. It is possible to add elements to a Redis List pushing new elements on the head (on the left) or on the tail (on the right) of the list.
The max length of a list is 2³² — 1 elements (4294967295, more than 4 billion of elements per list).

Posted Date:- 2021-11-15 06:52:34

Files will keep on growing as long as AOF executed. Won’t it consume more memory? What is the solution provided by redis?

Redis provides command BGREWRITEAOF which rewrites the existing AOF with the shortest sequence of commands needed to rebuild the current dataset in memory.

Posted Date:- 2021-11-15 06:51:20

Difference between Redis replication and sharding?

Replication is used to copy all data for getting high availibility of reads.It is also known as mirroring.
Sharding is used to splitting the data up by key and it also increases performance by reducing memory load on any one resource.It is also known as partitioning.

Posted Date:- 2021-11-15 06:50:20

How can you improve the durability in Redis?

To improve the durability of Redis “append only file” can be configured by using fsync data on disk.

* Fsync () every time a new command is added to the append log file: It is safe but very slow
* Fysnc() one time every second: It is fast, but you may lose 1 second of data if system fails
* Never fsync(): It is an unsafe method, and your data is in hand of Operating System

Posted Date:- 2021-11-15 06:48:25

Does Redis give speed and durability both?

No, Redis purposely compromises the durability to enhance the speed. In Redis, in the event of system failure or crash, Redis writes to disk but may fall behind and lose the data which is not stored.

Posted Date:- 2021-11-15 06:47:28

Which PHP module can be used with Redis?

In PHP module, PRedis is more preferable than Redid PHP binding or Resident

Posted Date:- 2021-11-15 06:46:56

How redis achive persistence by AOF?

AOF copies incoming write command to disk as they happen. It provides file synch options as follows.
a. always — Every writes to redis, writes to disk which usually affect redis’ performance.
b. everysec — Writes to disk every second
c. no — Let OS control syncing to disk

Posted Date:- 2021-11-15 06:46:22

How Redis achieve persistence by Snapshotting?

Snapshot takes the data as it exists at one moment in time & writes it to the disk, will be written to the file referenced as “dbfilename”.
There are 5 steps to initiate snapshots.
a. BGSAVE: When redis client initiate BGSAVE, redis will create a fork so that child process will write a the snapshot to the disk where master interacts with commands.
b. SAVE: When redis client initiate SAVE, redis will stop responding any commands until snapshot completes
c. From Configuration Files:
Example: Configuration as SAVE 60 10000
BGSAVE will be called if 10000 writes occure within 60 seconds
d. SHUTDOWN: When redis client sends a SHUTDOWN, redis will perform SAVE operations, blocks all operations, shutdowns later.
e. Sync with other Redis: If a Redis server connects to another server, it issues SYNC, then master Redis will start BGSAVE.

Posted Date:- 2021-11-15 06:45:56

Isn’t the Redis data lost if there’s a system crash?

To avoid data loss in case of system crash Redis provides persistence by Snapshotting & AOF(Append-only files).

Posted Date:- 2021-11-15 06:45:16

What is in-memory Database?

The in-memory database is a database where it keeps the dataset in RAM. Means that for every interaction with database, you will only access the Main memory; No DISK operations involved during this interaction. Hence the operation will be faster as it directly aceess main memoery instead of any disk operation.

Posted Date:- 2021-11-15 06:43:21

List the programming languages supported by Redis?

Redis supports a wide range of programming language. Some major programming languages supported by Redis are PHP, Java, Python, Scala, Perl, Ruby, C#, and C++.

Posted Date:- 2021-11-15 06:36:21

List some Redis Clients supported by PHP?

Below are some Redis Clients supported by PHP Programming Language
* amphp/redis
* cheprasov/php-redis-client
* Credis
* PHP Redis implementation / wrapper
* PHP Sentinel Client
* phpredis

Posted Date:- 2021-11-15 06:35:59

List the data structures supported by Redis.

Redis supports following Data Structures

* Strings
* Hashes
* Lists
* Sets
* Sorted sets with range queries
* bitmaps
* Hyperloglogs
* Geospatial indexes with radius queries

Posted Date:- 2021-11-15 06:35:00

What are Redis Hashes?

Redis hashes are defined as the hashes that map string names to string values. They are containers of unique fields and their values. It is a perfect way to represent an object as a Redis data structure. It provides constant time basic operations such as get, set, exists, etc.

Posted Date:- 2021-11-15 06:33:47

What is ZSET in Redis?

ZSET refers to the Redis Sorted Set where a Redis data type documented. In a sorted set, Each key has multiple values inside that is associated with a floating value score. In Redis, It has the unique property of being able to be accessed by a member like a HASH but items can also be accessed by the sorted order and values of the scores.

Posted Date:- 2021-11-15 06:32:54

Mention few LIST operations in REDIS.

LPUSH adds an element to the beginning of a list.

RPUSH add an element to the end of a list.

LPOP removes the first element from a list and returns it.

RPOP removes the last element from a list and returns it.

LLEN gets the length of a list.

LRANGE gets a range of elements from a list.

Posted Date:- 2021-11-15 06:32:17

REDIS is fast, but is it also durable?

No. Redis compromises with durability to enhance the speed. In Redis, in the case of system failure or crash, it writes to disk but may fall behind and lose the data which is not stored.

Posted Date:- 2021-11-15 06:31:44

What is redis-cli.

redis-cli is the Redis command-line interface, a simple program that allows sending commands to Redis, and read the replies sent by the server, directly from the terminal.

Posted Date:- 2021-11-15 06:31:23

Difference between SET and MSET command in REDIS.

SET command creates one key-value pair while using MSET command, multiple key-value pairs can be created.

Posted Date:- 2021-11-15 06:30:34

In which language Redis is developed?

Redis is developed using ANSI C and mostly used for cache solution and session management. It creates unique keys for store values.

Posted Date:- 2021-11-15 06:30:20

Explain Replication in Redis.

Redis supports simple master to slave replication. When a relationship is established, data from the master is replicated to the slave.

Posted Date:- 2021-11-15 06:27:26

What programming languages does Redis support?

REDIS supports most of the programming languages including Java, C#, Python, Scala, C++, R, PHP and many more.

Posted Date:- 2021-11-15 06:27:11

What are the advantages of Redis over a hash table?

Redis is not just an in-memory key/value (hash table) store rather it offers many other data types/structures to use. Apart from key/value you can store a List of strings, sorted by insertion order and can perform different list operations onto it.
Redis data persistence feature performs point-in-time snapshot of your in-memory data at specified intervals on file, so in case of server crash you can restore the cache again in no time.

Posted Date:- 2021-11-15 06:25:08

Why is Redis faster than SQL?

1. Since Redis stores data in primary memory, because of that Read and Write operations will be extremely fast.

2. In RDBMS, Read and Write operations are slow because it stores data in secondary memory.

3. Primary memory is in lesser in size and much expensive than secondary so, Redis cannot store large files or binary data.

Posted Date:- 2021-11-15 06:23:53

Why Redis is fast?

Redis is a data structure server. As a key-value data store, Redis is same as Memcached, but it has two major advantages over, support of additional datatypes and persistence. Since all of the data is stored in RAM, because of that system speed become extremely quick, sometimes perform even better that Memcached.

Posted Date:- 2021-11-15 06:22:42

What is Spring Session Data Redis?

Spring provides session repository for Redis database session management. In Spring Boot, we can make use of HTTPSession with Spring Session Data Redis to store the session data in persistent storage (Redis).

Posted Date:- 2021-11-15 06:22:24

What is in-memory Database

A database that holds the dataset in RAM is known as an in-memory database. This means that if you communicate with a database, you can only use Main memory; no DISK operations will be performed. As a result, the process will be quicker since it will access the main memory directly rather than using the disc.

Posted Date:- 2021-11-15 06:22:02

What is Redis?

Redis (Remote Dictionary Server) is an open-source in-memory data structure project implementing a distributed, in-memory key-value database 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.

Posted Date:- 2021-11-15 06:18:41

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