CAP Theorem

A run through of the CAP theorem using a Dynamo-based example. Talk given to my coworkers @ theScore.

Transcript

1. RIAK
2. A BRIEF DIVERSION...
3. A BRIEF DIVERSION...
4. DISTRIBUTED SYSTEMS
5. CAP THEOREM
6. CONSISTENCY AVAILABILITY PARTITION TOLERANCE
9. CONSISTENCY
10. A B chunky: ‘bacon’ chunky: ‘bacon’
11. A B chunky: ‘bacon’ chunky: ‘bacon’ chunky: ‘chicken’
12. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’
13. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’
14. A B chunky: ‘chicken’ chunky: ‘chicken’ chunky: ‘chicken’
15. A B chunky: ‘chicken’ chunky: ‘chicken’ chunky: ‘chicken’
16. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’
17. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’ ?
18. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’ chunky: ‘bacon’
19. A B chunky: ‘chicken’ chunky: ‘bacon’ chunky: ‘chicken’ chunky: ‘chicken’
20. “ATOMIC, OR LINEARIZABLE, CONSISTENCY IS THE CONDITION EXPECTED BY MOST WEB SERVICES TODAY. UNDER THIS CONSISTENCY GUARANTEE, THERE MUST EXIST A TOTAL ORDER ON ALL OPERATIONS SUCH THAT EACH OPERATION LOOKS AS IF IT WERE COMPLETED AT A SINGLE INSTANT. THIS IS EQUIVALENT TO REQUIRING REQUESTS OF THE DISTRIBUTED SHARED MEMORY TO ACT AS IF THEY WERE EXECUTING ON A SINGLE NODE, RESPONDING TO OPERATIONS ONE AT A TIME.”
21. “ATOMIC, OR LINEARIZABLE, CONSISTENCY IS THE CONDITION EXPECTED BY MOST WEB SERVICES TODAY. UNDER THIS CONSISTENCY GUARANTEE, THERE MUST EXIST A TOTAL ORDER ON ALL OPERATIONS SUCH THAT EACH OPERATION LOOKS AS IF IT WERE COMPLETED AT A SINGLE INSTANT. THIS IS EQUIVALENT TO REQUIRING REQUESTS OF THE DISTRIBUTED SHARED MEMORY TO ACT AS IF THEY WERE EXECUTING ON A SINGLE NODE, RESPONDING TO OPERATIONS ONE AT A TIME.”
22. AVAILABILITY
23. A B C D E
24. A B C D E
25. “FOR A DISTRIBUTED SYSTEM TO BE CONTINUOUSLY AVAILABLE, EVERY REQUEST RECEIVED BY A NON-FAILING NODE IN THE SYSTEM MUST RESULT IN A RESPONSE. THAT IS, ANY ALGORITHM USED BY THE SERVICE MUST EVENTUALLY TERMINATE … [WHEN] QUALIFIED BY THE NEED FOR PARTITION TOLERANCE, THIS CAN BE SEEN AS A STRONG DEFINITION OF AVAILABILITY: EVEN WHEN SEVERE NETWORK FAILURES OCCUR, EVERY REQUEST MUST TERMINATE.”
26. “FOR A DISTRIBUTED SYSTEM TO BE CONTINUOUSLY AVAILABLE, EVERY REQUEST RECEIVED BY A NON-FAILING NODE IN THE SYSTEM MUST RESULT IN A RESPONSE. THAT IS, ANY ALGORITHM USED BY THE SERVICE MUST EVENTUALLY TERMINATE … [WHEN] QUALIFIED BY THE NEED FOR PARTITION TOLERANCE, THIS CAN BE SEEN AS A STRONG DEFINITION OF AVAILABILITY: EVEN WHEN SEVERE NETWORK FAILURES OCCUR, EVERY REQUEST MUST TERMINATE.”
27. PARTITION TOLERANCE
28. A B C D E
29. A B C D E
30. “IN ORDER TO MODEL PARTITION TOLERANCE, THE NETWORK WILL BE ALLOWED TO LOSE ARBITRARILY MANY MESSAGES SENT FROM ONE NODE TO ANOTHER. WHEN A NETWORK IS PARTITIONED, ALL MESSAGES SENT FROM NODES IN ONE COMPONENT OF THE PARTITION TO NODES IN ANOTHER COMPONENT ARE LOST. (AND ANY PATTERN OF MESSAGE LOSS CAN BE MODELED AS A TEMPORARY PARTITION SEPARATING THE COMMUNICATING NODES AT THE EXACT INSTANT THE MESSAGE IS LOST).”
31. “IN ORDER TO MODEL PARTITION TOLERANCE, THE NETWORK WILL BE ALLOWED TO LOSE ARBITRARILY MANY MESSAGES SENT FROM ONE NODE TO ANOTHER. WHEN A NETWORK IS PARTITIONED, ALL MESSAGES SENT FROM NODES IN ONE COMPONENT OF THE PARTITION TO NODES IN ANOTHER COMPONENT ARE LOST. (AND ANY PATTERN OF MESSAGE LOSS CAN BE MODELED AS A TEMPORARY PARTITION SEPARATING THE COMMUNICATING NODES AT THE EXACT INSTANT THE MESSAGE IS LOST).”
33. ?
35. ?
36. A B C D E
37. A B C D E
38. A B C D E
39. A B C D E
40. A B C D E
41. A B C D E
42. A B C D E
43. A B C D E
44. WRITES
45. A B C D E
46. A B C D E
47. B A C D E
48. B A C D E
49. B A C D E
50. B A C D E
51. READS
52. A B C D E
53. B A C D E
54. B A C D E
55. B A C D E
56. ...
57. A B C D E
58. MAJORITY
59. A B C D E
60. A B C D E
61. CONSISTENT
62. N W R REPLICAS WRITE SUCCESS READ SUCCESS
63. (N/2) + 1
64. R+W > N
65. FAIL
66. A B C D E
67. A B C D E
68. YOU GET THE CHOICE
69. R+W <= N
70. A B C D E
71. W=N, R=1
72. R=N, W=1
73. TUNE FOR C OR A
74. CAN’T HAVE BOTH
75. CAN’T REALLY DO MUCH MORE ABOUT P
76. IT’S A BUSINESS DECISION