Redis

Redis is a NOSQL database in which data is stored in key-value pairs.
Redis stores data on main memory meaning its fast but its volatile unlike database systems like PostgreSQL which stores data on disk.

Overview

In an application with a server and a database, accessing information on the database will cause latency.

Key-Value databases like redis is often kept in front of those databases and access operations takes 2 steps:

1. If the information is in the cache, cache hit, the application retreives the information from redis and sends it to the client
2. If not, cache miss, the application takes the information from the database , sends it to the client and stores it in the cache.

With these 2 steps and given that main memory has lower latency than disk, we can say that redis can be used to store and access frequent, recent data and expensive operations thereby making applications 10 to 50x faster.

It is thereby a fact that if at all you are going to building an application that is going to be scalable in the future, Redis(or databases similar to Redis) is indispensable.

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Questions

1. Is Redis Open Source?: Yes, Redis is open source with a special kind of license but there are alternatives like KeyDB by Snapchat and Memcached that are open source. KeyDB is a fork of Redis but as of now can only run on Linux.

2. Does Redis Support Windows?: No, Redis does not support Windows, but you can install WSL/Ubuntu and install redis using
   

sudo apt install redis

1. I am using WSL, Why isn't redis server working on my system: When running on WSL, you can run redis-server using

redis-server --port 6000

where 6000 is the port on your local server you want to run it on. (i.e. 127.0.0.1:6000).

Most issues are due to the fact that the default port that redis-server is using is already being used

1. Are there client libraries for Redis?: Actually yes. you can find them on the Redis website or you can build one yourself.

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Installing Redis

On Linux, installing redis is as simple as

sudo apt install redis

or on Mac:

brew install redis

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Running Redis

You need to have 2 instances of your terminal on

on the first one to run your server

redis-server -port <portnumber>
</portnumber>

and on the second one to run your client

redis-cli

When building a web app, you dont need to run the client but the server needs to be running

Redis Concepts

There are 3 main concepts in redis you should understand or 4

1. Key-Value Pairs
2. Lists
3. Sets
4. Hashes

All other data structures are mainly an advanced implementation of the first

By list, I meant array not linked list and thats what redis calls it.

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Key-Value Pairs

Key-Value pairs are a common data structure in most programming languages.

1. In Python it is called dictionaries or dict in short

2. In Javascript it is called Maps

3. In C# it is called Dictionaries

There are 6 main operations for key-value pairs in Redis

Operations	Explanations	Examples	Further Explanation
SET	Creates a key-value pair	SET name John	Sets key to map to value
GET	Gets value for key	GET name	This returns John
DEL	Deletes the key value pair	DEL name	This removesthe key value pair name from the database
EXISTS	Checks if a key exists in the redis database	EXISTS name	returns 1 or 0 corresponding to True or False
FLUSHALL	Clears the entire cache	FLUSHALL	more or less like DROP TABLE in postgres
KEYS *	Returns all the keys in the database	KEYS *

There are also Time-Based Operations. In time based operations, the key is only in the cache for a set amount of time, after the time expires, the cache deletes the key.

There are 2 main Time Based Operations

Operations	Explanations	Examples	Further Explanation
EXPIRE	Expires a key after being defined	EXPIRE name 10	Deletes the key-value name after 10s .The key must be defined with SET before calling EXPIRE . A common alternative is;
SETEX	Expires a key upon definition	SETEX age 30 15	Sets the key age to value 30 and thereafter deleted the key-value pair after 15s
TTL	Time To Live	TTL age	Returns the time remaining before deletion of the age key

The Blog is getting too long now, I will talk about lists, sets, hashmaps and also possible interview questions about redis in another blog.

Please if you have questions, please comment them down below, I will try my best to answer them ⭐. Happy Coding

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