Redis is an open source advanced key-value store, created by antirez. Here is a quick overview of this awesome NoSql DB. Like a swiss knife, Redis will help you by many ways : LRU cache, high scores, UID generator, queues, social feeds, autocomplete …

1. ARE YOU REDIS TO GO ?
MAXIME LEMAITRE – 10/04/2014
1

2. > GET agenda
> GET introduction
> SMEMBERS datatypes
> INFO commands
> CLIENT LIST
> PSUBSCRIBE performance?
> LRANGE features 0 3
persitence
transaction
replication
pubsub
> ZREVRANGE usecases 0 -1
> SEGFAULT
> ?
I see Redis definitely more as a flexible tool
that as a solution specialized to solve a
specific problem: his mixed soul of cache,
store, and messaging server shows this
very well - Salvatore Sanfilippo (antirez),
creator of Redis
2

3. Brief Introduction
• Redis is an open source (since March 2009), advanced key-value
store. It is often referred to as a data structure server since keys
can contain strings, hashes, lists, sets and sorted sets.
• Originally written in order to help address the scaling needs of
http://lloogg.com/, a web analytics startup, by Salvatore (antirez)
Sanfilippo.
• Redis is written in ANSI C and works in most POSIX systems like
Linux, *BSD, OS X and Solaris without external dependencies. Redis
project does not directly support Windows, however MSOpenTech
develops and maintains an Windows port targeting Win64.
3

4. Command Processing
http://redis.io/commands
• Protocol RESP
– clients communicate with the Redis using REdis Serialization Protocol
• Simple, Fast & Human readable
– Commands are processed in serial in a single thread (like Node.js)
• Superfast processing of commands (a few ms, sometimes less)
• If you want to use more CPUs, shard your data client-side
• Command groups
– Request/response
– Pipelined: Several requests / responses
– Transactions:
• Traditional: Several requests processed in order atomically
• Check-And-Set: Request(s), data manipulation in client, more
requests
– Scripts (>v2.6): execute client-defined Lua scripts in the server for
more complex actions 4

5. What is a Command ?
http://redis.io/commands
Command name + parameters >
Version >
Complexity (really important) >
Description >
Result/return value >
Example >
Approx. 160 available
commands 5

6. Data Types
List Set Sorted Set Hash
[A, B, C, D]
“A”
“B”
“C”
“D”
D
C
B
A
A:3
C:1
D:2
B:4
{A, B, C, D} {C:1, D:2, A:3, D:4}
“A”
“B”
“C”
“D”
field1
field2
field3
field4
{field1:“A”, field2:“B”…}
{value:score} {key:value}
Basically maps keys to values (Strings), but also contains more advanced data
structures here :
* New Data Structure since April, 1st : HyperLogLog 6

7. Popular .net clients
Many clients for nearly all languages
• ActionScript
• C / C++
• C#
• Clojure
• Lisp
• Dart
• Erlang
• Fancy
• Go
• Haskell
• haXe
• Io
• Java
• Lua
• Node.js
• Objective-C
• Perl
• PHP
• Python
• Ruby
• Scala
• Smalltalk
• Tcl
7

8. How fast is Redis ?
(note : it’s common a manage millions of keys)
Redis includes the redis-benchmark utility that simulates running commands done by
N clients at the same time sending M total queries.
• Example on Intel(R) Xeon(R) CPU E5520 @ 2.27GHz (without pipelining)
Commands are generally processed in a few ms. Network
bandwidth and latency usually have a direct impact on the
performance. CPU is another very important factor. 8

9. Redis Feature : Persistence
http://redis.io/topics/persistence
Redis provides a different range of persistence options: RDB, AOF and None.
• RDB
– Periodic, asynchronous dump to disk
– Can be every N changes or every N seconds
– Written to file in “dbfilename”.rdb (could be backup elsewhere)
– may loss several minutes during a crash
• AOF
– Copies incoming commands as it happens
– Log-based, redo whole steps since startup
– Still fast enough, but often limited by disk performance
– may loss a few seconds during a crash
• None
– Keep data only in Memory.
9

10. Redis Feature : Transaction
http://redis.io/topics/transactions
• Multiple actions can be put into a transaction
– execute multiple command in a single step.
– Either all of the commands or none are processed
• Command MULTI to start transaction
– EXEC to execute
– DISCARD to discard
– WATCH for Optimistic locking
• Guarantees:
– Executed in the defined order
– Atomic (all or nothing)
– No isolation
– Can use optimistic locking
> MULTI
OK
> INCR pageviews:count
QUEUED
> EXPIRE pageviews:count 60
QUEUED
> SADD pageviews http://google.fr
QUEUED
> EXPIRE pageviews 60
QUEUED
> EXEC
1) (integer) 4660294
2) (integer) 1
3) (integer) 569023
4) (integer) 1 10

11. Redis Feature : Replication
http://redis.io/topics/replication
• Redis uses classic master / slave replication
• Slaves can replicate to other slaves (in a graph-like structure)
• Replication does not block the master/slave (async)
• Boost scalability & allow redundancy
 Scaling performance by using the replicas for intensive read
operations.
 Making data redundant in multiple locations.
 Offloading data persistency costs from the master by
delegating it to the slaves
> SLAVEOF PAR-REDIS01:6379
> SLAVEOF PAR-REDIS01:6379
> SLAVEOF PAR-REDIS01:6379
11

12. Redis Feature : PubSub
http://redis.io/topics/pubsub (my favorite)
• A client can subscribe some topics, and when someone publish topic matches the
interest (topic), redis send it to it.
• Clients can subscribe to channels (eg user:1245) or patterns (eg user:*)
• Subscribing is O(1), posting messages is O(n)
• Use cases : Think chats, real-time analytics, twitter, …
CLIENT 1
> PSUBSCRIBE user:*
psubscribe
user:*
1
…
//wait notification
…
pmessage
user:*
user:1000
themessage
EMITTER 1
> PUBLISH user:1001 themessage
1 //number of message sent
Keyspace Notifications (>2.8) allows client to receive events
affecting the Redis data set (commands affecting a given key,
expiration, any command processed, …)
2
12

13. Use case #1 : Who’s online ?
//cybermaxs has 3 friends
> SADD cybermaxs:friends maxs
> SADD cybermaxs:friends nicocanicola
> SADD cybermaxs:friends oinant
//cybermaxs connects
> SADD users:online cybermaxs
//maxs connects
> SADD users:online maxs
//oinant connects
> SADD users:online oinant
Who’s online ?
> SMEMBERS users:online
Maxs
oinant
cybermaxs
Are cybermaxs’s friends online ?
> SINTER users:online cybermaxs:friends
maxs
oinant
Is nicocanicola connected ?
> SISMEMBERS users:online nicocanicola
0
How many connected users ?
> SCARD users:online
3
13

14. Use case #2 : leaderboard
> ZADD leaderboard 1543 cybermaxs
> ZADD leaderboard 4564 nicocanicola
> ZADD leaderboard 8954 toto
> ZADD leaderboard 6164 oinant
> ZADD leaderboard 9642 cybermaxs
> ZADD leaderboard 4123 toto
> ZADD leaderboard 8713 maxs
How to get top 3 ?
> ZREVRANGE leaderboard 0 2
WITHSCORES
cybermaxs
9642
toto
8954
maxs
8713
How to get rank of player X ?
> ZREVRANK leaderboard oinant
3
How to get score of player X ?
> ZSCORE leaderboard toto
8954
How to add score to player ?
> ZINCRBY leaderboard 3000
nicocanicolas
7563
SELECT TOP 10 * FROM leaderboard
WHERE ... ORDER BY score DESC ?
14

15. > INCR questions:nextid
1234 //last question id was 1233
> HMSET question:1234 title “Are you Redis to go?"
asked_by “cybermaxs“ votes 0
OK //add question to redis
> LPUSH questions question:1234
1 //add to list
> SADD question:1234:tags redis nosql
2 //add to tags
// later upvote by a user
> HINCRBY question:1234 votes 1
1
> ZINCRBY tagged:redis 1 question:1
1
Use case #3 : StackExchange Clone
Lastest 200 questions for Homepage
> LRANGE questions 0 199
question:200
question:199
…
Get Votes for a question
> HMGET question:1234 votes
2
Get Tags for a question
> SMEMBERS question:1234
redis
nosql
Questions by Tags, Sorted by Votes
> ZREVRANGE tagged:redis 0 5
question:1234
question:486
…
Subscribe to all changes on a question
> SUBSCRIBE __key*question:1234
+ Socket.IO
/SignalR
15

16. Common uses cases
• Cache out-of-process
• Duplicate detector
• FIFO/LIFO Queue
• Priority Queue
• Distributed hashmap
– e.g. url shortener
• UID generator
• Game high scores
• Geolocation lookup
– lat & long -> city
• Real-time analytics
• Metrics DB
• API throttling (rate-
limits)
• Autocomplete
• Twitter
• digg / Hacker News
• Social activity feed
• …
16

17. Who is using Redis ?
17

18. Conclusion
18

19. Questions
(mine : are you Redis to Go ?)
19

20. References
• http://redis.io/
• http://en.wikipedia.org/wiki/Redis
• http://try.redis.io/ (online introduction)
• http://redis.io/topics/data-types-intro
• http://highscalability.com/blog/2011/7/6/11-common-web-use-cases-solved-in-
redis.html
• http://oldblog.antirez.com/post/take-advantage-of-redis-adding-it-to-your-
stack.html
• http://mono.servicestack.net/docs/redis-client/designing-nosql-database
• http://fr.slideshare.net/dvirsky/kicking-ass-with-redis
• http://fr.slideshare.net/noahd1/redis-in-practice
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21

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