The aim of this talk is to give a brief introduction to Redis, and then show a few practical examples of what we can actually do with it. First presented at the Great Western Rails meetup in Bristol, hosted by Cookpad to foster the Ruby community in the south west!

1. 101

2. What’s Redis?
key / value store

3. Why Redis?
It’s fast
Add it, don’t switch
Open source
Great Ruby support

4. Who uses Redis?

5. Who uses Redis?

6. What’s Redis?
key / value store

7. What’s Redis?
key / string
key / hash
key / list
key / set
key / sorted set

8. key / string
What can we do?
● Store any data we like (up to 512MB)

9. key / string

10. Setup
require "redis"
redis = Redis.new(host: "192.168.0.1", port: 6380, db: 1)

11. key / string
Example
redis.set(key, value)
redis.set "meetup:5", "Great Western Rails - May 18"
=> "OK"
redis.get "meetup:5"
=> "Great Western Rails - May 18"

12. key / string
Use case: Analytics
redis.set request.fullpath, 0
=> "OK"
10_400.times { redis.incr request.fullpath }
redis.get request.fullpath
=> "10400"

13. key / string
Rails
class ApplicationController
before_action :count_visit
private
def count_visit
redis.incr(request.fullpath)
end
end
class ProductsController < ApplicationController
def show
@hits = redis.get(request.fullpath)
end
end

14. key / hash
What can we do?
● Store a hash
● Basically unlimited
● Get specific fields
● Get all fields
● Increment value
key: {
"field1"=>"value",
"field2"=>"value"
}

15. key / hash
Use case: Comments with voting

16. key / hash
Use case: Comments with voting
redis.mapped_hmset "comment:1", {
body: "Wow. Great post. 👍",
upvotes: 1,
downvotes: 0
}
=> "OK"

17. key / hash
Use case: Comments with voting
redis.mapped_hmset "comment:1", { body: "Wow. Great post. 👍", upvotes: 1, downvotes: 0 }
=> "OK"
redis.hincrby "comment:1", "upvotes", 1
=> 2

18. key / hash
Use case: Comments with voting
redis.mapped_hmset "comment:1", { body: "Wow. Great post. 👍", upvotes: 1, downvotes: 0 }
=> "OK"
redis.hincrby "comment:1", "upvotes", 1
=> 2
upvotes = redis.hget("comment:1", "upvotes").to_i
downvotes = redis.hget("comment:1", "downvotes").to_i
score = upvotes - downvotes
=> 1

19. key / list
What can we do?
● Store a list (Array)
● Order is maintained
● Maximum length 4294967295
● Add to beginning or end, trim, get range of values

20. key / list
Use case: Social media feed

21. key / list
Use case: Social media feed
Jane
follows
Tweet.where(author: current_user.following).order(created_at: :desc)

22. key / list
Use case: Social media feed
Jane

23. key / list
Example
tweet = Tweet.create(author: current_user, body: "Hello, world")
tweet.author.followers.each do |follower|
redis.lpush "user:#{follower.id}:feed", "tweet:#{tweet.id}"
end

24. key / list
Example: Most recent tweets
# LRANGE key, start, stop
redis.lrange "user:2:feed", 0, 9

25. key / set
What can we do?
● Store a unique list of members
● Order not guaranteed
● Check difference and intersection
● Check if set contains member

26. key / set
Example: Follower / Following

27. key / set
Example
redis.sadd "user:2:following", ["user:5", "user:1", "user:10"]
=> 3
redis.sadd "users:2:following", "user:10"
=> false
redis.smembers "user:2:following"
=> ["user:10", "user:5", "user:1"]

28. key / set
Example
# Is user 2 following user 10?
redis.sismember "user:2:following", "user:10"
=> true
# Is user 2 following user 11?
redis.sismember "user:2:following", "user:11"
=> false

29. key / set
Example
redis.sadd "user:10:following", ["user:4", "user:19", "user:1", "user:12"]
redis.sadd "user:2:following", ["user:5", "user:1", "user:10"]
# Who are both users following?
redis.sinter "user:2:following", "user:10:following"
=> ["user:1"]

30. key / sorted set
What can we do?
● Similar to a set
● Score for each item
● Sorted!
● Fetch by score

31. key / sorted set
Use case: Leaderboard

32. key / sorted set
Example
redis.zadd "eurovision", 500, "Australia"
redis.zadd "eurovision", 529, "Israel"
redis.zadd "eurovision", 170, "Moldova"
redis.zadd "eurovision", 0, "United Kingdom"

33. key / sorted set
Example
redis.zadd "eurovision", 500, "Australia"
redis.zadd "eurovision", 529, "Israel"
redis.zadd "eurovision", 170, "Moldova"
redis.zadd "eurovision", 0, "United Kingdom"
redis.zrevrange "eurovision", 0, -1, with_scores: true
=> [["Israel", 529.0], ["Australia", 500.0], ["Moldova", 170.0], ["United Kingdom", 0.0]]

34. Combine
key / string
key / hash
key / list
key / set
key / sorted set

35. Thank you 😃
Lewis Buckley
@lewispb