README.md
# Learn Redis
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Need to store/access your data as ***fast*** as possible? Try Redis!
## [Why?](https://youtu.be/zeXv4bav54M?t=9s)
> "*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**](https://github.com/antirez/redis/tree/unstable/src)
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*](http://try.redis.io)
***before*** installing Redis:
+ [**SET**](http://redis.io/commands/set) - SET a the value for a given key.
+ [**GET**](http://redis.io/commands/get) - GET the value of a key.
+ [**INCR**](http://redis.io/commands/incr) increment a counter (*integer*)
+ [**DECR**](http://redis.io/commands/decr) decrement a counter (decremented key needs to already exist)
```sh
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](http://brew.sh/) installed, simply run this command in your terminal:
```sh
brew install redis
```
#### Windows?
> See: http://stackoverflow.com/questions/6476945/how-do-i-run-redis-on-windows
<br />
### Which Node.js Module?
A search for "redis" on **NPM**: https://www.npmjs.com/search?q=redis returns *many* results!
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](https://github.com/redis/hiredis) **C Library**.
This means its ***much faster*** than "*Pure JavaScript*" code.
Its faster, so what's the catch?
> If you (or anyone on your *team*) using [*Microsoft Windows*](https://youtu.be/WTYet-qf1jo?t=56s)
> (*stop hitting yourself!*)
> will need to install a
> [*compiler*](http://stackoverflow.com/questions/5691795/how-to-compile-c-programming-in-windows-7)
> 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***](https://github.com/dwyl/redis-connection) to re-use a *single* connection across all files/modules in a project.
The [***redis-connection***](https://github.com/dwyl/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***](https://github.com/dwyl/redis-connection)
Install:
```sh
npm install redis-connection --save
```
Use:
```js
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**
```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:
```sh
$ 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***](http://redis.io/commands/append) lets us *add* data to record
without having to read it first. ()
```sh
redis> EXISTS mykey
(integer) 0
redis> APPEND mykey "Hello"
(integer) 5
redis> APPEND mykey " World"
(integer) 11
redis> GET mykey
"Hello World"
```
+ [**incr**ment](http://redis.io/commands/incr) a value (e.g a ***counter***) no
delay having to *read* the current value *before* you can increase it by one.
```sh
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**](http://redis.io/commands/expire) means you can delete data after a specified amount of time.
e.g: expire a key after 10 seconds
```sh
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**](http://redis.io/commands/rpush)
+ [**LPUSH**]()
+ [**LRANGE**]()
```sh
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***](http://redis.io/topics/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***](http://en.wikipedia.org/wiki/Atomicity_%28database_systems%29).
+ [***PubSub***](http://redis.io/commands/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
+ ***What is Redis*** and what do I **use it for**? (good list of **usecases**)
http://stackoverflow.com/questions/7888880/what-is-redis-and-what-do-i-use-it-for
+ Redis Wikipedia: http://en.wikipedia.org/wiki/Redis (history and background)
+ Good **comparison** of **NoSQL** datastores: http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-vs-redis
+ Why ***Redis beats Memcached*** for caching:
http://www.infoworld.com/article/2825890/application-development/why-redis-beats-memcached-for-caching.html
+ ***Why*** **Redis is Awesome**:
http://www.robupcraft.com/why-redis-is-awesome
+ Memcached vs. Redis? (good list feature/comparison)
http://stackoverflow.com/questions/10558465/memcached-vs-redis
+ Is Redis "just" a cache? http://stackoverflow.com/questions/10137857/is-redis-just-a-cache
+ What are the differences between MongoDB and Redis? (v. basic)
http://stackoverflow.com/questions/6445899/what-are-the-differences-between-mongodb-and-redis
+ How to Pipeline in node.js to Redis:
http://stackoverflow.com/questions/21416529/how-to-pipeline-in-node-js-to-redis
+ List of Redis Features:
https://redis-docs.readthedocs.org/en/latest/Features.html
+ 11 Common Web Use Cases Solved In Redis:
http://highscalability.com/blog/2011/7/6/11-common-web-use-cases-solved-in-redis.html
+ How to Install and use Redis on Ubuntu
https://www.digitalocean.com/community/tutorials/how-to-install-and-use-redis
### 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
+ https://addons.heroku.com/rediscloud ***free*** plan is **30mb**
+ https://addons.heroku.com/redistogo *free* plan is **5mb** (paid plans are quite expensive per MB, but they have great service - hence being the #1 provider...)
+ https://addons.heroku.com/redisgreen *no free* plan. #fail (also quite expensive per MB and no distinguishing features)
+ https://addons.heroku.com/openredis *no free* plan. #fail (commitment to use the latest version of redis is good. notifications when reaching 90% of memory.
> ***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:
Select RedisCloud Free plan and add to your heroku app:
Confirm its been enabled
Go to `Settings` and Click to view the `Config Vars` then grab the `REDISCLOUD_URL` Config Variable so you can use it:
Now you can export it and use it in your node.js app:
```sh
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
+ Redis Tips (Mozilla): https://developer.mozilla.org/en-US/docs/Mozilla/Redis_Tips
+ Using Redis as an LRU cache: http://redis.io/topics/lru-cache
+ Travis-CI gives you access to Redis:
http://docs.travis-ci.com/user/database-setup/#Redis
(see: **.travis.yml** *this* repo for an example)
#### Performance & Benchmarks
+ How fast is Redis? http://redis.io/topics/benchmarks
+ Storing ***hundreds of millions*** of simple key-value pairs in Redis **INSTAGRAM ENGINEERING** Blog:
http://instagram-engineering.tumblr.com/post/12202313862/storing-hundreds-of-millions-of-simple-key-value
+ Redis Labs Achieves Over ***1.2 Million Transactions per Second*** on a **Single** Amazon Web Services (AWS) **Instance**:
http://www.marketwired.com/press-release/redis-labs-achieves-over-12-million-transactions-per-second-on-single-amazon-web-services-1965269.htm
#### 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.
+ Redis **persistence** ***demystified***: http://oldblog.antirez.com/post/redis-persistence-demystified.html
#### Graphical User Interface (GUI) for Viewing/Setting Data
+ Redis Commander https://github.com/joeferner/redis-commander is
a node module (express app) you can install and run,
then open a web browser to View/Set your Data
##### Alternative GUIs
+ Redsmin https://redsmin.com (really useful for Redis instances hosted in the Cloud, forever free for 1 server)
+ Redis Desktop Manager https://github.com/uglide/RedisDesktopManager (an installed desktop app)
+ List of others: https://redislabs.com/blog/so-youre-looking-for-the-redis-gui
#### 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**](http://en.wikipedia.org/wiki/Riak) - great for fault tolerance and data replication
+ [**LevelDB**](http://leveldb.org/) - Bundled with node.js so always available, but limited on heroku.
+ [**RethinkDB**](http://www.rethinkdb.com/) - Probably the coolest real-time database on the planet! :sunglasses:
+ and *of course* [***Redis***](http://redis.io/) - *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: **RE**mote **DI**ctionary **S**erver
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*"](http://en.wikipedia.org/wiki/Associative_array#Example)
and would *look* like this:
```js
{
"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**](http://en.wikipedia.org/wiki/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'.
```js
// 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:
```js
// 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:
### 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***?"
MongoDB is a good tool. We like to think of it as
[the ***Hammer*** of Databases](http://en.wiktionary.org/wiki/if_all_you_have_is_a_hammer,_everything_looks_like_a_nail)
... 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***.
### 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?](http://stackoverflow.com/questions/16375188/redis-strings-vs-redis-hashes-to-represent-json-efficiency)
Alternately, use [flat](https://github.com/hughsk/flat) as described in [Store Javascript objects in Redis with Node.js the right way](https://medium.com/@stockholmux/store-javascript-objects-in-redis-with-node-js-the-right-way-1e2e89dbbf64).
# 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/