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SimardeepSingh1450
SimardeepSingh1450

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Redis Caching in 4 minutes

What is caching and why even use it in the first place ?
Caching means storing remote-data locally on your system for faster re-access.

What do I mean by faster re-access ?
Suppose there is a large Database(DB) of posts, the user wants to access one post out of such a large DB. Each time the user wants to access a post it will take some-time since the system will search in sequential order in DB for the specified post.
Example - I want to see the data of post-7, then the data would be sequentially searched in the DB, hence taking time.

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So how to reduce this request-response wait-time ?
Hence steps in caching, redis-caching can be used with node-express API to make fetching data faster. With redis-caching an in-memory data-store is created which inturn creates key-value pairs thus providing faster retreival of data.
Whenever we search for a post-data in DB, our API will then first check if the key is present in redis-datastore, if present then returns the data with less-time and quick-response, else we can cache(store) the not cached-data, creating new key-value pair in its data-store for quick data retreival on re-access of same data accessed earlier.

Redis Key-Value DataStore Demonstration :

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NOTE - You can also find the below source-code at :
https://github.com/SimardeepSingh1450/redis-in-4-minutes

So lets start making our own redis-API :

First of all, you need to install redis on your machine :
Visit http://redis.io and setup redis-server.

Create a folder with : mkdir myRedisApi
Go inside the folder : cd myRedisApi and create index.js file.

In terminal type below command to create package.json file :

npm init -y
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In terminal type below command to install required npm packages :

npm i redis express nodemon
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Start your local machine redis-server in terminal :

redis-server
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It may look like this :

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Now in your index.js put the below code to create a simple express API :

const express = require('express');

const app = express();
app.use(express.json());

app.listen(8080,()=> {
    console.log('Server is listening on port-8080');
})
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Now make the following changes in your package.json :

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Now open another terminal to start this server type :

npm run devStart
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Now put the redis-setup code in this order in index.js :

const express = require('express');
const redis = require('redis');

//redis-setup-code
const redisUrl = "redis://127.0.0.1:6379"
const client = redis.createClient(redisUrl);
client.connect();
client.on('connect',(err)=>{
    console.log('Redis connected!')
})

const app = express();
app.use(express.json());
...
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Here redisUrl = redis://localhost:portNumber and redis.createClient(redisUrl) creates our client for connecting to
redis-server.

Paste the below code in index.js for performing operations:
1.Storing new {key,value} pairs in redis-datastore using POST request :

app.post('/setKeyValue',async(req,res)=>{
    const {key,value} = req.body;
    console.log(key,value);
    await client.set(key,JSON.stringify(value));
    console.log(`${key}:${value} has been set`)
    res.json(`${key}:${value} has been set`);
})
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2.Retrieving the stored {key,value} pairs from redis using the GET request :

app.get('/:key',async(req,res)=>{
    const key = req.params.key;
    let cachedData = await client.get(key);
    if(cachedData){
        res.json(JSON.parse(cachedData));
    }else{
        res.json(`The Key(${key}) has no matching value in redis`)
    }
})
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Your final index.js code should be like this :

const express = require('express');
const redis = require('redis');

//redis-setup-code
const redisUrl = "redis://127.0.0.1:6379"
const client = redis.createClient(redisUrl);
client.connect();
client.on('connect',(err)=>{
    console.log('Redis connected!')
})

const app = express();
app.use(express.json());

app.post('/setKeyValue',async(req,res)=>{
    const {key,value} = req.body;
    console.log(key,value);
    await client.set(key,JSON.stringify(value));
    console.log(`${key}:${value} has been set`)
    res.json(`${key}:${value} has been set`);
})

app.get('/:key',async(req,res)=>{
    const key = req.params.key;
    let cachedData = await client.get(key);
    if(cachedData){
        res.json(JSON.parse(cachedData));
    }else{
        res.json(`The Key(${key}) has no matching value in redis`)
    }
})

app.listen(8080,()=> {
    console.log('Server is listening on port-8080');
})
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Testing our redis-datastore using Postman :
1.POST Request :

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2.GET Request :

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You can clearly see that it took only 9ms for the response, thus fast retreival of the data.

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You have now gained the knowledge to implement redis in any API, hence time for some homework :

Try making a redis API with a Database such as MongoDB, MySql, etc. and see the difference in data response-time with and without implementation of redis.

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