Caching Memcached vs. Redis

Transcription

1 Caching Memcached vs. Redis San Francisco MySQL Meetup Ryan Lowe Erin O Neill 1

2 Databases WE LOVE THEM... Except when we don t 2

3 When Databases Rule Many access patterns on the same set of data Transactions (both monetary and isolated units of work) Don t know what the end state access patterns will be Always :) 3

4 When Databases Suck Lots of concurrent users ORMs Big Data Sets Small Pockets of VERY hot data 4

5 How Caching Works External vs. built-in caching MySQL Query Cache InnoDB Buffer Pool Rails SOMETHING 5

6 Caching Architecture Becomes 6

7 Why Caching Works 7

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10 There are only two hard problems in Computer Science: cache invalidation, naming things, and off-byone errors. -- Martin Fowler 10

11 Problems with Caching Cache Misses Thundering Herd Stale Data Warm-Up Times Overly-Aggressive Caching Poor Cache Design 11

12 Cache Misses Cache Hit: 1 Operation Cache Miss: 3 Operations 12

13 Thundering Herd Key TOP_10_VIDEOS 9:00 Generating the K/V takes three seconds Page gets 100 req/s = 100*3 = 300 threads! 13

14 Stale Data Must maintain consistency between the database and the cache from within the application Extremely difficult to validate correctness 14

15 Cache Warm-Up All attempts to read from the cache are CACHE MISSES, which require three operations. This can result in a significant degradation of response time. Usually accompanied by a Thundering Herd 15

16 Use Cases Sessions Popular Items Full Page Cache Profile Information User Preferences Tag Clouds Auto-suggest lists Relationships User Information Online Users Statistics 16

17 Memcached Memcached is an in-memory keyvalue store for small chunks of arbitrary data (strings, objects) from results of database calls, API calls, or page rendering. 17

18 Redis Redis is an open source, 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. 18

19 In-Memory Means We re Bound By RAM 19

20 Consistent Hashing Each Key deterministically goes to a particular server. Think (KEY % SERVERS) 20

21 Memcached Dead Simple & Battle Tested Fast Non-Blocking get()/set() Multi-Threaded Consistent Hashing 21

22 Memcached Example employee_id = 1234 employee_json = { name => Ryan Lowe, title => Production Engineer } set(employee_id, employee_json) get(employee_id) [Returns employee_json] 22

23 But I don t want all the data What if I just want the name? 64 Bytes for the object vs. 10 for just the name :-( 6x network traffic More work for the application Fatter applications 23

24 Redis Advanced Data Types Replication Persistence Usually Fast Very Cool Atomic Operations 24

25 Redis: The Bad Single-Threaded Limited client support for consistent hashing Significant overhead for persistence (do be discussed later) Not widely deployed (compared to Memcached) 25

26 Redis: Datatypes Strings (just like Memcached) Lists Sets Sorted Sets Hashes 26

27 Redis: Lists Stored in sorted order Can push/pop Fast head/tail access Index access (yay) 27

28 Redis: Lists r.lpush( employees, Ryan Lowe ) r.lpush( employees, Dave Apgar ) r.lrange( employees, 0, -1) ( Dave Apgar, Ryan Lowe ) r.rpush( employees, Evan Miller ) r.lrange( employees, 0, -1) ( Dave Apgar, Ryan Lowe, Evan Miller ) 28

29 Redis: Sets Un-ordered collections of strings Unique (no repeated members) diff, intersect, merge 29

30 Redis: Sets sadd( employees, Ryan Lowe ) sadd( former_employees, Bryan Lowe ) sdiff( former_employees, employees ) ( Ryan Lowe, Bryan Lowe ) 30

31 Redis: Sorted Sets Same as Sets but ordered by a score 31

32 Redis: Hashes r.hset( employees, count, 1234) r.hset( employees, females, 1000) r.hset( employees, males, 234) hget( employees, count ) 1234 hgetall( employees ) { count => 1234, females => 1000, males => 234 } 32

33 Memcached vs. Redis Memcached Redis (multi)get (multi)set incr/decr delete Expiration prepend/append Range Queries Data Types! Persistence (sorta) Multi-Threaded Replication (sorta) 33

34 Instrumentation Redis: info Memcached: stats Both give system information, connections, hits, misses, etc. Graphite most of the metrics!!! 34

35 Benchmarks 35

36 About the Benchmarks 1 Hour Redis 2.6 & Memcached ,000,000 Keys "KEY_#{i.to_s}" 51-Character Values (0...50).map{ ('a'..'z').to_a[rand(26)] }.join 36

37 Redis Benchmarks 37

38 Redis Set (1 Server) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

39 Redis Set (1 Server) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients WTF?! 39

40 Redis Set (1 Server) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients

41 Redis Set (2 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

42 Redis Set (2 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients WTF?!

43 Redis Set (4 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

44 Redis Set (8 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

45 Hash Ring Balance (%) 100 Server 1 Server Redis Memcached 45

46 Hash Ring Balance (%) 50 Server 1 Server 2 Server 3 Server Redis Memcached 46

47 Hash Ring Balance (%) Server 1 Server 2 Server 3 Server 4 Server 5 Server 6 Server 7 Server Redis Memcached 47

48 Redis Get (1 Server) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

49 Redis Get (2 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

50 Redis Get (4 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

51 Redis Get (8 Servers) 1 Client 2 Clients 4 Clients 8 Clients 12 Clients 16 Clients 24 Clients 32 Clients

52 The Cost of Persistence Redis No Persistence Redis BGSAVE (FIO) Redis AOF

53 Redis & Memcached Benchmarks 53

54 Set Operations (1 Server, 24 Clients) Memcached Redis

55 Get Operations (1 Server, 24 Clients) Memcached Redis

56 Set Operations (2 Servers, 24 Clients) Memcached Redis

57 Get Operations (2 Servers, 24 Clients) Memcached Redis

58 Set Operations (4 Servers, 24 Clients) Memcached Redis

59 Get Operations (4 Servers, 24 Clients) Memcached Redis

60 Set Operations (8 Servers, 24 Clients) Memcached Redis

61 Get Operations (8 Servers, 24 Clients) Memcached Redis

62 Conclusions Redis inconsistent under heavy load We need more benchmarks! (Redis) Datatype-specific Big Memory (Redis) Big Keys 62

63 Questions? 63