2014-09-22 | redis - the basics (viennadb)

The Basics

Dominik Gruber, @the_dom ViennaDB – Sep. 22, 2014

Dominik Gruber • @the_domRedis

Agenda• What Is Redis?

• Operations / Data Types

• Transactions

• Scripting

• Use Cases


Dominik Gruber

• Work at KURIER.at online network

• Many services, among them events.at–which makes use of Redis

• Studied “Software Engineering & Internet Computing” at Vienna University of Technology

http://KURIER.at

http://events.at


Fun Facts• Redis = REmote DIctionary Server

• Initial release in 2009

• Most recent version: 2.8.17

• Written in C

• Libraries for 30+ programming languages

• Good documentation


Redis

“Redis is an open source, BSD licensed, advanced key-value cache and store. It is often

referred to as a data structure server since keys can contain strings, hashes, lists, sets,

sorted sets, bitmaps and hyperloglogs.”


Redis• Redis is an in-memory but persistent on disk database

• 1 Million small Key -> String value pairs use ~ 100 MB of memory

• Single threaded – but CPU should not be the bottleneck

• Average Linux system can deliver even 500k requests per second

• Limit is likely the available memory in your system

• max. 232 keys


Differences to Memcached• Memcached is a “distributed memory object caching system”

• Redis persists data to disk eventually

• Memcached is an LRU cache

• Redis has different data types and more features

• Memcached is multithreaded

• Similar speed


Prominent Adopters• Twitter

• Pinterest

• Tumblr

• GitHub

• Stack Overflow


Operations / Data Types


Basics

• SET key value [EX seconds] [PX milliseconds] [NX|XX]

• GET key

• DEL key

!

• Possible Use Case: Caching


Basics

• EXISTS key

• KEYS pattern

• EXPIRE key seconds

• MGET key [key …]

• MSET key value [key value …]


Strings

• STRLEN KEY

• APPEND key value


Integer

• INCR key / INCRBY key increment

• DECR key / DECRBY key increment

!

• Possible Use Case: Track Ad- or Page-Impressions


Hashes• HSET key field value

• HGET key field

• HGETALL key

• HDEL key field [field …]

!

• Possible Use Case: Session Storage


Lists• LSET key index value

• LPUSH key value [value …] / RPUSH key value [value …]

• LPOP key / RPOP key

• LRANGE key start stopl

• LREM key count value

• Possible Use Cases: Task queue, Last modified items (with paging)


Sets• SADD key member [member …]

• SMEMBERS key / SRANDMEMBER key [count]

• SSCAN key cursor [MATCH pattern] [COUNT count]

• SISMEMBER key member

• SPOP key

• SREM key member [member …]

• Possible Use Case: Index items by category


Sets: Operations

• SINTER key [key …] / SINTERSTORE destination key [key …]

• SDIFF key [key …] / SDIFFSTORE destination key [key …]

• SUNION key [key …] / SUNIONSTORE destination key [key …]


Sorted Sets• ZADD key score member [score member …]

• ZSCORE key member

• ZRANGEBYSCORE key min max [WITHSCORES] [LIMIT offset count]

• ZREM key member [member ...]

• ZREMRANGEBYLEX key min max

• ZINCRBY key increment member

• Possible Use Case: Scoreboards, Track time-based events


HyperLogLog

“Hyperloglog is an approximate technique for computing the number of distinct entries in a set

(cardinality). It does this while using a small amount of memory. For instance, to achieve 99% accuracy, it

needs only 16 KB. “

– Wikipedia


HyperLogLog

• PFADD key element [element …]

• PFCOUNT key [key …]

• PFMERGE destkey sourcekey [sourcekey ...]

!

• Possible Use Case: Track Unique Visitors


Pub/Sub

• SUBSCRIBE channel [channel …]

• UNSUBSCRIBE [channel [channel …]]

!

• PUBLISH channel message


Transactions

• MULTI

• EXEC

• DISCARD


Transactions

WATCH mykey val = GET mykey val = val + 1 MULTI SET mykey $val EXEC !


Scripting

• Execute Lua scripts on the server side

• EVAL script numkeys key [key ...] arg [arg …]

!

• SCRIPT LOAD script

• EVALSHA sha1 numkeys key [key ...] arg [arg ...]


Scripting: ExampleRandomPushScript = <<EOF local i = tonumber(ARGV[1]) local res math.randomseed(tonumber(ARGV[2])) while (i > 0) do res = redis.call('lpush',KEYS[1],math.random()) i = i-1 end return res EOF !r.del(:mylist) puts r.eval(RandomPushScript,1,:mylist,10,rand(2**32))


Use Cases


Resque• “Resque is a Redis-backed Ruby library for creating background

jobs, placing them on multiple queues, and processing them later.”

• Comes with a web interface

• Developed by GitHub

• https://github.com/resque/resque

• https://github.com/blog/542-introducing-resque

https://github.com/resque/resque

https://github.com/blog/542-introducing-resque


Typeahead Completion• ZRANGEBYLEX key min max [LIMIT offset count]

• ZRANGEBYLEX uses plain binary comparison

!

• ZADD autocomplete 0 apricot 0 apple 0 banana 0 brocolli 0 brinjal

• ZRANGEBYLEX autocomplete [br [br(0xff)

!

• ZADD 0 mango:{"name":"Mango Smoothie Recipe"}0 smoothie:{"name":"Mango Smoothie Recipe"}0 recipe:{"name":"Mango Smoothie Recipe"}


Q & A


Source

• http://redis.io

• http://highscalability.com

• http://www.cucumbertown.com/craft/autocomplete-using-redis-nginx-lua/

http://redis.io

http://highscalability.com

http://www.cucumbertown.com/craft/autocomplete-using-redis-nginx-lua/

2014-09-22 | redis - the basics (viennadb)

Technology

zremrangebylex key

redis redis

key valuedominik redis

eval script numkeys

key keys pattern

strings strlen key

advanced keyvalue cache

casesdominik redis gruber