/learn-redis

:closed_book: Need to store/access your data as fast as possible? Learn Redis! Beginners Tutorial using Node.js :rocket:

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Learn Redis

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Need to store/access your data as fast as possible? Try Redis!

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Why?

"40% of people will leave your site if it takes longer than 3 seconds to load..."
https://econsultancy.com/blog/10936-site-speed-case-studies-tips-and-tools-for-improving-your-conversion-rate
Never make people wait; Learn how to cache your content/app with Redis.

Storing data is a necessity for all (but the simplest) web applications.
Often accessing that data can be the biggest bottleneck in an app causing it to be slow and painful experience.
Redis is designed to be the fastest way to store and retrieve data.
Which means less waiting for the people using your app!

What?

Redis is the closest you can get to direct access (to your computer's) memory.
Written in C the entire server is less than a Megabyte (smaller is better when it comes to executable size), Redis is built for speed.

### Use Case

  • sessions in your app (which require a DB/io read on every request but don't contain content) should be checked/set as quickly as possible.
  • list online people in a chat application the list of people/devices that are connected changes frequently (as people join/leave). Wouldn't it be useful to be able to subscribe to this list and be notified when it changes?
  • content cache given that Redis can store any size of string, it can store any content you need to serve in your app; from simple components to entire pages.

How?

First Learn the Fundamentals

First thing you need to do - if you haven't already - is go through the online tutorial: http://try.redis.io/ (30mins to learn and take notes)

#### Make Sure you Understand

You can learn/practice all these commands online before installing Redis:

  • SET - SET a the value for a given key.
  • GET - GET the value of a key.
  • INCR increment a counter (integer)
  • DECR decrement a counter (decremented key needs to already exist)
redis> SET count 10
redis> GET count
"10"
redis> INCR count
(integer) 11
redis> DECR count
(integer) 10

Easy, Right? lets keep moving.

Installation

If you don't already have Redis installed on your machine - why would you if you're reading an introductory tutorial, right? - there are two three ways to install Redis:

The guys who make Redis suggest compiling it from source (this requires a working GCC compiler and libc) see: Quick Start: http://redis.io/topics/quickstart
If you are running Linux/Mac or prefer not to use Vagrant, try the download & compile described in the quickstart.

installing using (home)brew (Mac Only)

Once you have homebrew installed, simply run this command in your terminal:

brew install redis

brew-install-redis

Windows?

See: http://stackoverflow.com/questions/6476945/how-do-i-run-redis-on-windows


Which Node.js Module?

A search for "redis" on NPM: https://www.npmjs.com/search?q=redis returns many results!

npm-search-redis

Don't be overwhelmed by the quantity of modules, focus on quality.

The 2 modules we use and recommend for connecting to Redis

  • redis https://www.npmjs.com/package/redis written in "Pure JavaScript" this is by far the most popular node module for Redis, and... if you install it with: npm install redis hiredis then it will use the C binding for speed.
  • hiredis-node https://github.com/redis/hiredis-node is a JS wrapper around the hiredis C Library.
    This means its much faster than "Pure JavaScript" code. Its faster, so what's the catch?
    npm-install-hiredis

If you (or anyone on your team) using Microsoft Windows (stop hitting yourself!) will need to install a compiler
to get Redis working and that can sometimes take hours!

Update: Our experience lead us to create redis-connection

Given that it easy to open too many connections to redis we created redis-connection to re-use a single connection across all files/modules in a project. The redis-connection module is just a few lines you can read/understand in 5 mins and takes the hassle out of creating (and closing) connections see:

Our recommendation is to use the redis module for simple apps, but for anything more interesting (e.g: an app that has handlers spread across several files) we recommend using redis-connection

Install:

npm install redis-connection --save

Use:

var redisClient = require('redis-connection')();
redisClient.set('hello', 'world');
redisClient.get('hello', function (err, reply) {
  console.log('hello', reply.toString()); // hello world
});

Basic Example

See: examples/basic.js

Paste hand-type (or copy-paste) this code into a file called basic.js

var redisClient = require('redis-connection')();

redisClient.set("Hello", "World", redis.print);

redisClient.get("Hello", function(err, reply) {
   // reply is null when the key is missing
   console.log('Hello ' + reply);
});

Run the script in your terminal by issuing the command: node basic.js You should expect to see:

$ node basic.js
Reply: OK
Hello World

Also Good To Know but Not Essential for this Introductory Tutorial

Redis has many fantastic features not limited to just SET/GET/DELETE key:value pairs. You can also atomically

  • append lets us add data to record without having to read it first. ()
redis> EXISTS mykey
(integer) 0
redis> APPEND mykey "Hello"
(integer) 5
redis> APPEND mykey " World"
(integer) 11
redis> GET mykey
"Hello World"
  • incrment a value (e.g a counter) no delay having to read the current value before you can increase it by one.
redis> SET mykey "10"
OK
redis> INCR mykey
(integer) 11
redis> GET mykey
"11"

If you don't get overwhelmed by lots of new words and want a sneak peek
at the all the cool commands you can use in Redis check: http://redis.io/commands But we're getting ahead of ourselves, lets focus on the basics first.

  • EXPIRE means you can delete data after a specified amount of time. e.g: expire a key after 10 seconds
redis> SET mykey "Hello"
OK
redis> EXPIRE mykey 10
(integer) 1
redis> TTL mykey
(integer) 10
# wait for 10 seconds then
redis> TTL mykey
(integer) -2

  • TTL (time to live) lets you check how long it will be before a key (and its associated value) will expire from the cache. (see expire example above)

  • Lists - A list is a series of ordered values (comparable to an Array in JS)

RPUSH fruits "Apple"
RPUSH fruits "Banana"
LPUSH fruits "Mango"
LRANGE fruits 0 -1 => 1) "Mango", 2) "Apple", 3) "Banana"
LRANGE fruits 0 1 => 1) "Mango", 2) "Apple"
LRANGE fruits 1 2 => 1) "Apple", 2) "Banana"
LLEN fruits => 3

  • Sets - Redis Sets are an unordered collection of Strings. It is possible to add, remove, and test for existence of members in O(1) (constant time regardless of the number of elements contained inside the Set). SISMEMBER tests if the given value is in the set. It returns 1 if the value is there and 0 if it is not.

  • Data Types: http://redis.io/topics/data-types

  • Transactions allow the execution of a group of commands in a single step, with two important guarantees:

    • All the commands in a transaction are serialized and executed sequentially. It can never happen that a request issued by another client is served in the middle of the execution of a Redis transaction. This guarantees that the commands are executed as a single isolated operation.
    • Either all of the commands or none are processed, so a Redis transaction is also atomic.

  • PubSub lets you "listen" for changes in the value of a key. Useful if you want to know when something has been changed by someone. e.g: you have two devices (Desktop & Mobile) logged into an app, something gets updated on one of them, how do we reflect this change on the other? Answer: all devices "subscribe" to the change event and receive the latest values as a result.

Practical Simple Example Using Redis & Node.js

A "Hit Counter" to track how many people have viewed your GitHub Repository: https://github.com/nelsonic/hits

Advanced (Real) Example

For a more complete example featuring "Publish/Subscribe" for real-time interactivity, see our Chat App: https://github.com/dwyl/hapi-socketio-redis-chat-example

Background Reading

General

Publish / Subscribe

Probably the most useful feature of Redis for building real-time apps is publish/subscribe. Thankfully, Thoughtbot have written a good post explaining it: https://robots.thoughtbot.com/redis-pub-sub-how-does-it-work

Their article uses Ruby (they are still a rails shop...) but our Practical tutorial uses node.js, so after you have read the intro, checkout: https://github.com/dwyl/hapi-socketio-redis-chat-example

Which Redis-as-a-Service (Heroku Addon)?

There are a few options for hosted Redis on Heroku: https://addons.heroku.com/?q=redis

Conclusion: rediscloud!

Get your RedisCloud Instance

The easiest way to get your RedisCloud instance is to create a Heroku app and add the RedisCloud Addon to it.

In your heroku app, click on Resources, type redis into the search box: learn-redis-01-find-addon

Select RedisCloud Free plan and add to your heroku app: learn-redis-02-select-rediscloud

Confirm its been enabled learn-redis-03-enabled

Go to Settings and Click to view the Config Vars then grab the REDISCLOUD_URL Config Variable so you can use it: learn-redis-04-config-vars

Now you can export it and use it in your node.js app:

export REDISCLOUD_URL=redis://rediscloud:yourpassword@pub-redis-12345.eu-west-1-2.1.ec2.garantiadata.com:12345

Which you can then access in your node.js app using process.env.REDISCLOUD_URL

Tips and Tricks

Performance & Benchmarks

Persistence

Because Redis is an in-memory datastore, persistence is not immediate. if you want to be sure that your data is saved, (incase your server/instance is re-booted) read about using the SAVE command.

Graphical User Interface (GUI) for Viewing/Setting Data

Alternative GUIs

Key-Value (KV) Store

There are many KV Stores to chose from: http://en.wikipedia.org/wiki/NoSQL#Key-value_stores our favourites are:

  • Riak - great for fault tolerance and data replication
  • LevelDB - Bundled with node.js so always available, but limited on heroku.
  • RethinkDB - Probably the coolest real-time database on the planet! 😎
  • and of course Redis - fast, free and fun!

We're here to focus on Redis because it has the right balance of simplicity (great for beginners and pros alike) and speed.

Frequently Asked Questions (FAQ)

### Q: What does Redis mean/stand for?

The name Redis is an acronym for: REmote DIctionary Server

A Dictionary (see: http://xlinux.nist.gov/dads/HTML/dictionary.html) is another way of saying "Key-Value Store";
In other programming languages a dictionary is known as a "map" or "associative array" and would look like this:

{
  "firstName": "John",
  "lastName": "Smith",
  "isAlive": true,
  "age": 25,
  "address": {
    "streetAddress": "21 2nd Street",
    "city": "New York",
    "state": "NY",
    "postalCode": "10021-3100"
  },
  "children": [],
  "spouse": null
}

The observant reader will notice that this looks exactly like a JSON Object; that's because it is! This is how we represent a set of key:value pairs in JS.

It can be easy to think of the real-world dictionary, words are the keys and their definitions are the values.
Imagine you are the person writing the definitions in a dictionary,
you would specify the key (e.g: 'everything') for your item in the dictionary and "SET" the value (e.g: 'awesome').
Then, when you read (or "GET") record for the 'everything' key the value would be 'awesome'.

// basic key:value lookup in JavaScript. Try it: http://repl.it/jYk
var dictionary = {
  'everything':'awesome'
}
for (var k in dictionary) {
  console.log(k + ' is ' + dictionary[k]); // everything is awesome
} // whaaaat? >> https://youtu.be/StTqXEQ2l-Y

Or, sticking with the dictionary metaphor, here's a better example:

// basic key:value dictionary lookup in JavaScript. Try it: http://repl.it/jYk/4
var dictionary = {
  'bycycle':'A bicycle, often called a bike or cycle, is a human-powered, \
pedal-driven, single-track vehicle, having two wheels attached to a frame, \
one behind the other.'
}
for (var k in dictionary) {
  console.log(k +': ' +dictionary[k] );
}

output:

bicycle-definition

Q: Can't I Just Use MongoDB for Everything?

"We are already using MongoDB to store our records, can't we just put everything in one place?"

which-tool-job-hammer-mongodb-fry-futurama-millionaire

MongoDB is a good tool. We like to think of it as the Hammer of Databases
... a general purpose Datastore that works well for most NoSQL situations.
But if you need to save/access Millions of Records Per Second (yes, you read that right!)
then there's only one place to store your data; Redis.

there can be only one

Q: Can we use Redis as Primary Datastore?

Yes! Do it! Discover the power of data structures and the speed of an in-memory datastore!

Q: How should we store JSON?

Redis strings vs Redis hashes to represent JSON: efficiency? Stackoverflow: Redis strings vs Redis hashes to represent JSON: efficiency?

Alternately, use flat as described in Store Javascript objects in Redis with Node.js the right way.

Last But Not Least

Highly recommend reading Redis In Action to anyone wanting to use Redis professionally. see: http://www.amazon.com/Redis-Action-Josiah-L-Carlson/dp/1617290858 For educational purposes see: http://www.it-ebooks.info/book/2447/