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RedisGet more than a cache back!Maarten Balliauw@maartenballiauw
Who am I?
Maarten Balliauw Antwerp, Belgium Developer Advocate, JetBrains Founder, MyGet Focus on web & cloud http://blog.maartenballiauw.be @maartenballiauw
Agenda
Redis Data types Transactions Pub/sub Scripting Sharding/partitioning Patterns
Redis
Redis
“Redis is an open source, BSD licensed, networked, single-threaded, in-memory 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.”
REmote DIctionary Server
Redis
Key-value cache and store (value can be a couple of things) In-memory (no persistence, but you can) Single-threaded (atomic operations & transactions) Networked (it’s a server and it does master/slave) Some other stuff (scripting, pub/sub, Sentinel, snapshot, …)
Things to remember
Persistence?
Dump memory to disk (faster restore after restart)
AOF (append-only files) RDB (Redis DB snapshots)
With or without: all your data must fit in memory
Redis 101demo
The Little Redis Book
http://openmymind.net/redis.pdf
By Karl Seguin
Data types
Type Example Key Example valueString cache:/home <html><head><title>Home
page</title>Hash categories:1 Field
namedescriptionnumproducts
MemberShipsPirate ships for sale50000
Set categories:1:products 20 11 56 89 32 4List products:20:comments [0] -> “That skull flag is awesome!”
[1] -> “Parrot bit my finger, not happy!”[2] -> “Parrot keeps swearing at me.”
Sorted set products:bestsellers FieldEye PatchParrot
Score8463282120
+ Bitmap, Hyperloglog
Data typesdemo
Data types
Type Example Key Example valueString cache:/home
user:nextid<html><head><title>Home page</title>2
Hash user:1 Fieldnamehandle
MemberMaarten@maartenballiauw
Set user:1:followers 10 42 99 85List user:1:timeline [0] -> { ... }
[1] -> { ... }[2] -> { ... }
Sorted set trending:no:tags Field#ndcoslo#redis
Score8463282120
+ Bitmap, Hyperloglog
Keys
Good practice: use a pattern for keys E.g. users:1:maarten Get by id: KEYS users:1:* GET ...... Get by name: KEYS users:*:maarten
GET ...... O(N) operation – use with caution!
Connecting to Redis (C# / Node – pick one!)demo
Transactions
MULTI, EXEC, DISCARD, WATCH No rollbacks (just discard queue) Failures are because of you, not Redis Optimistic locking with WATCH Only execute transaction queue if watched keys did not
change
Transactionsdemo
Pub/Sub
(P)SUBSCRIBE, UNSUBSCRIBE, PUBLISH Subscribe to a queue SUBSCRIBE news (or PSUBSCRIBE news:*) Send data to a queue PUBLISH news “This just in!” (optional) Keyspace notificationshttp://www.redis.io/topics/notifications
CONFIG SET notify-keyspace-events KEA PSUBSCRIBE '__key*__:*' (or __keyspace@0__:foo)
Pub/Subdemo
Scripting
Run Lua scripts on Redishttp://www.redis.io/commands/eval
EVAL ‘return “Hello, World!”’ 0 Scripts are cached (SCRIPT FLUSH) Scripts can be used as functions Although we must pass the body all the time (or use SCRIPT LOAD +
EVALSHA) Helper functions available! Base, table, string, math, debug, struct, cjson, cmsgpack, redis.sha1hex
Scriptingdemo
What if I need more memory?
Sharding On client (consistent hashing) Using a proxy (Twemproxy -
https://github.com/twitter/twemproxy) Cluster On server (Redis Cluster) tip: always connect to >= 2 nodesvar Redis = require('ioredis');
var cluster = new Redis.Cluster([ { port: 6380, host: '127.0.0.1' }, { port: 6381, host: '127.0.0.1' }]);
cluster.set('foo', 'bar');cluster.get('foo', function (err, res) { // ... });
Patterns
When can I use Redis?
Output cache Session state General-purpose cache (e.g. for database) “Cache with benefits” Pub/sub Generally: when use case maps and data fits in RAM
When should I avoid Redis?
More data than can fit in RAM Can use multiple, but even then: SUM(RAM) == max. data
size Data and query model fits well in a relational model
Materialize certain queries in Redis if needed Avoid Redis for large objects... ...with lots of concurrent read/write operations
Counting stuff
How would you count “likes” if you were Facebook?
SQL UPDATE posts SET likes = likes + 1 WHERE postid = 1234 Locking! Will slow down the application... Redis INCR post:12345 (Every once in a while, check keys to persist)
Counting stuff (+ popularity)
And how would you get the 5 most popular posts?
Use a sorted set Elements are scored (= # of likes) We can use ZREVRANGE to get the top X posts ZREVRANGE posts:likes 0 5 withscores
Get the latest 5 product reviews
No need to go to the database! Use a Redis List, truncated at 5 items Need more? Query the database
Rate limiting
API should only allows 5 requests per 60 seconds Redis List
Record 5 latest requests If we’re at 5, check the leftmost item versus current time
1 2 3 4 512:20:25 12:20:22 12:20:21 12:20:18 12:19:50
Autocompletion
How to provide autocompletion over our million-records product catalog?
SQL “LIKE” Lucene / ElasticSearch Redis Sorted Set
Intersecting collections
“Which friends do we have in common?”
Algorithm could be: Find friends that we have in common Find friends they have in common Score the # of connections
Sort
We have a series of bugsPriority, Status, Title, ...
A user follows a few of these bugsHow to store?How to query? (give me my top 5 bugs by priority) hset bugs:1 priority 5
hset bugs:2 priority 2hset bugs:3 priority 1
SORT bugsifollow BY bugs:*->priority
Conclusion
Conclusion
Redis is not just a cache Data types Transactions Pub/sub Scripting Sharding/partitioning Patterns 1 thing to remember: http://openmymind.net/redis.pdf
Thank you!http://blog.maartenballiauw.be@maartenballiauw
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