Redis Labcamp

REDIS Labcamp
Angelo Simone Scotto
Cluster Reply

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• Developed by Salvatore Sanfilippo for his startup Merzia S.r.l.
• Aimed as a fast replacement of MySQL for web analytics (LLOOGG)
• Released as open source
in 2009.
• Sponsored by VMWare
since 2010.
• Sponsored by Pivotal
since 2013.
• Currently part of backend
of
An italian story
• Twitter
• Github
• Pinterest
• StackOverflow
• Flickr
• …

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What is REDIS (REmote DIctionary Service)
Redis is a DSL (Domain Specific Language) that manipulates abstract data
types and implemented as a TCP daemon. Commands manipulate a key
space where keys are binary-safe strings and values are different kinds of
abstract data types.
REDIS Manifesto

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Available Abstract Data Types
Key-Value Store:
• Keys
 Printable ASCII
• Values
 Primitives
 Strings
 Containers (of strings)
 Hashes
 Lists
 Sets
 Sorted Sets
Other Functionalities
 Pub/Sub
 HyperLogLog
 Bitmaps

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Where to find Redis
• Obviosuly at redis website : http://redis.io
• Redis written in ANSI C and POSIX compliant:
• Linux (supported and recommended)
• Mac OS X (supported)
• *BSD (supported)
• Solaris (support defined «Best effort»)
• Windows is not directly supported by REDIS Project but
• Microsoft mantains and support a version at
http://msopentech.com/opentech-projects/redis/
• Used by Microsoft in Azure (Azure Redis Cache Service) therefore stable
and usable also on windows.

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How to Install Redis
• On Windows, very simple:
• Download binaries from
https://github.com/MSOpenTech/redis/tree/2.8/bin/release, unzip and run.
• On Linux or MacOSX:
• Your preferred Package Manager (apt-get, YUM …) should have it but it’s
usually not recommended because often lagging behind current version.
• Recommended way is to recompile binaries directly:
http://redis.io/download

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Strings
Redis Key
Value: Redis String
• Max Value Size: 512 MB
• Binary Strings
Commands:
• GET, SET
• INCR, DECR, INCRBY, DECRBY
• GETBIT, SETBIT, BITCOUNT, BITPOS, BITOP
• APPEND, GETRANGE, SETRANGE
• MGET, MSET

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Hashes
• Max Value Size: 512 MB
• Binary Strings
Redis Key
Value: Redis Hash
Field 1 Value 1
Field 2 Value 2
Field 3 Value 3
Commands:
• HGET, HSET
• HINCRBY, HINCRBYFLOAT
• HLEN, HGETALL, HVALS, HKEYS
• HMGET, HMSET

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Lists
• LPUSH, LPOP (Left, first)
• RPUSH, RPOP (Right, last)
• Queues are simply lists
when using LPUSH & RPOP
• Stack are simply lists when
using LPUSH & LPOP
• Index (list) operations are
obviously available
(LINDEX)
Redis Key
Value: Redis List
HEAD
Value1
Valuen
TAIL
Commands:
• LPUSH, LPOP
• RPUSH, RPOP, RPOPLPUSH
• BLPOP, BRPOP, BRPOPLPUSH
• LINDEX, LRANGE, LREM

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Sets
• Unsorted set
• Unique Values (duplicates
are non inserted)
Redis Key
Value: Redis Set
Value 2
Value 1
Value 4
Value 5
Value 3
Commands:
• SADD, SPOP, SREM
• SCARD, SISMEMBER
• SUNION, SDIFF, SINTER
• SUNIONSTORE, SDIFFSTORE, SINTERSTORE

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Sorted Sets
• Score is a float (double precision
floating number).
• Unique Values (duplicates are non
inserted)
• Sorted sets are sorted by their score in
ascending way
Redis Key
Value: Redis Sorted Set
Value1
Score100
Value2
Score200
Value3
Score200
Value4
Score250
Commands:
• ZADD, ZREM
• ZCARD, ZRANGE, ZREVRANGE
• ZSCORE, ZCOUNT, ZINCRBY, ZRANGEBYSCORE
• ZLEXCOUNT, ZRANGEBYLEX, ZREVRANGEBYLEX, ZREMRANGEBYLEX
• ZUNIONSTORE, ZINTERSTORE

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Other Functionalities
Bitmaps:
 Not really a type, just a set of operators on strings.
Publish / Subscribe:
 Not a type, it implements a fire&forget publish/subscribe engine.
 PUBLISH, SUBSCRIBE, UNSUBSCRIBE
 PSUBSCRIBE, PUNSUBSCRIBE
HyperLogLog:
 Value contains an HyperLogLog algorithm implementation.
 REDIS implementation uses 12K per key with a std error of 0.81% to
count 2^64 items.
 PFADD, PFCOUNT, PFMERGE

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REDIS Architecture
Key points:
• Extremely Fast.
• i.e. Data is always in RAM.

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REDIS Architecture
Key points:
• Extremely Fast.
• Extremely Simple.
• i.e. REDIS is single-threaded.

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REDIS Architecture
Key points:
• Extremely Fast.
• Extremely Light.

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REDIS Architecture
Key points:
• Extremely Fast.
• Extremely Light.
• Extremely Robust.

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REDIS Architecture
Security:
«Redis is not optimized for maximum
security but for maximum performance
and simplicity»
• AUTH with password.
• BIND to specific network interface.
• No encryption (use SSL proxy)
• No ACS (each connection is admin)
• Possible to RENAME sensible
commands…

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REDIS Architecture
Persistence:
• None.
• RDB (Redis DB) single-file dump.
• AOF (Append Only File), a log file.
• No fsync (fast, not safe).
• Fsync each second.
• Fsync each query (slow but safe).
• Both
Memory Usage:
• Data is always in memory, you cannot have more data than RAM in REDIS.
• Virtual Memory deprecated.
• Disk Store abandoned.
• Several policies to manage overflow:
• noeviction: no action, just error.
• allkeys-lru: remove older data
• allkeys-random: remove rnd data
• volatile-lru: remove expirable
• volatile-random: remove expirable
• volatile-ttl: remove expirable

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REDIS Architecture
Transactions:
• Not an ACID Transactions.
• All commands are serialized and
executed sequentially (MULTI).
• Either all commands or no commands
are processed (EXEC – DISCARD).
• Keys must be explicitely specified in
Redis transactions (WATCH)
• Less useful since lua scripting appeared.
• Commands Available:
• WATCH / UNWATCH
• MULTI
• EXEC / DISCARD

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REDIS Architecture
Lua Scripting:
• Lua is a small, fast, simple embeddable
scripting language.
• EVAL command takes script, keys and
arguments:
• Redis calls are done through
redis.call or redis.pcall functions:
• Scripts are executed sequentially on the
server in atomic way

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A Swiss Army Knife for Programmers
Redis gives you a small, light, efficient
remote datastore with persistence, high-
availability, scalability and publish/subscribe
functionalities.
Use is limited just by your imagination:
• Shared Configuration.
• Distributed Lock.
• Caching.
• Work Queues.
• Load Balancers.
• Service Discovery.
• …

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A super-simple blog platform
• Use the frontend and the language you prefer:
• Frontend:
• Console Application
• Web Application
• Form Application
• Language:
• List of supported clients: http://redis.io/clients
• 5 Levels of features (10 points):
1. User Management (2 points)
2. Post Management (2 points)
3. Tags / Categories (2 points)
4. Votes (2 points)
5. New posts notification (2 points)

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User Management
• System should be able to register new users, login existing users and
show registered users.
• Each user should have a unique id (number), a username, a password
• Conventions:
• A common convention is to use hierarchical names for keys
separated by ‘:’ such as blog:users:1 or blog:users:1:posts
• Tip:
• Use String and INCR to manage unique ids.
• Use Hashes to manage user objects
• Use Set to guarantee uniqueness of usernames

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Post Management
• A logged in user should be able to add a blog post.
• Each post will have a unique id (number), a content, a timestamp and a
subject.
• Given a user the system should return the list of items posted by the
user.
• Tip:
• Use String and INCR to manage unique ids.
• Use Hashes to manage post objects.
• Use Lists to relate posts with owners

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Tags / Categories
• Modify the previous post structure to keep also a set of tag for each
post.
• Given a tag the system should return all posts tagged with it.
• Given multiple tags the system should return all posts, if any, tagged
with them.
• Tip:
• Add Tags field to post Hash.
• Use Sets to manage categories, and SINTER to search for multiple
tags.

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Votes
• A logged in user should be able to vote posts.
• Each user must be able to vote just once for a post.
• System should be able to show posts ordered by votes.
• Tip:
• Use Sorted Sets to manage post ranks.
• Use Sets to enforce one vote per user per post.

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Push Notifications
• A user could express interest for a category (tag) or another user activity.
• System should notify user if an article is posted in a category he
expressed interest into.
• System should notify user if an article is posted by a user he expressed
interest into.
• Tip:
• Use PubSub engine to manage notifications.
• Use one channel per category and one channel per user.

Thanks
Angelo Simone Scotto
a.scotto@reply.eu

Redis Labcamp

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