Distributed Computing. Using multiple sites to solve a problem

Transcription

1 Distributed Computing Using multiple sites to solve a problem 1

2 Distributed Computing Using multiple sites to solve a problem Network filesystem 2

3 Distributed Computing Using multiple sites to solve a problem Network filesystem Cloud computing

4 Distributed Computing Using multiple sites to solve a problem Network filesystem Cloud computing Multi-player game

5 Distributed Computing Using multiple sites to solve a problem Network filesystem Multi-player game Cloud computing Collaborative spreadsheet 5

6 Distributed Computing Using multiple sites to solve a problem Network filesystem Multi-player game Cloud computing Collaborative spreadsheet E-commerce site 6

7 Distributed Computing Using multiple sites to solve a problem Network filesystem Multi-player game E-commerce site Cloud computing Collaborative spreadsheet Scientific simulation 7

8 Distributed Computing Using multiple sites to solve a problem Network filesystem Multi-player game E-commerce site Cloud computing Collaborative spreadsheet Scientific simulation Monitoring a volcano 8

9 Distributed Computing Using multiple sites to solve a problem Network filesystem Multi-player game E-commerce site Monitoring a volcano Cloud computing Collaborative spreadsheet Scientific simulation Searching for aliens 9

10 Distributed Computing Different applications different levels of transparency: Hardware as a service: use of multiple computer is automatic for each application Volcano-monitoring sensors: distribution and communication explicit in the application Different applications same core problems: Synchronization Possibility of failure (site or communication) 10-11

11 Happens Before <wizard image> <knight image> <dragon image> 15

12 Virtual Clocks <wizard image> <knight image> <dragon image> mumbling muttering sleeping breathing fire sheilding 16

13 Virtual Clocks <wizard image> <knight image> <dragon image> mumbling sleeping muttering sheilding breathing fire 17

14 Virtual Clocks <wizard image> <knight image> <dragon image> mumbling sleeping muttering sheilding breathing fire 18

15 Virtual Clocks <wizard image> <knight image> <dragon image> breathing 1 19

16 Virtual Clocks <wizard image> <knight image> <dragon image> breathing 20

17 Mutual Exclusion and Locks 21

18 Centralized Lock One site manages a given lock Advantages: Simple to implement Easy to make fair Disadvantages: Lock manager might fail 22-26

19 Distributed Lock Ask everyone else s permission for lock Advantages: Disadvantages: Lots of communication One failure prevents use of lock 27-0

20 Majority Lock Ask permission from more than 50% for lock Advantages: Handles failure of sites well Less communication than asking everyone Disadvantages: Still lots of communication 1-5

21 Token Ring Wait for permission, then pass it on afterward Advantages: Relatively little communication Clearly fair Makes sense when permission is needed often Disadvantages: Have to set up ring Single failure breaks the ring Extra work when permission is needed rarely 6-0

22 Elections In case sites need to pick a new coordinator (e.g., for a lock) Bully algorithm Ring algorithm 1

23 Bully Algorithm Rank all sites If a process i doesn t hear back from a coordinator: Send an elect message to every j > i No responses? Then i considers itself elected and notifies everyone Got response? Wait for notify from new coodinator... If a process i receives an elect message, treat it like not hearing from the coordinator 2

24 Bully Algorithm 1 2

25 Bully Algorithm 1 2

26 Bully Algorithm 2 5

27 Bully Algorithm 2 wait on 6

28 Bully Algorithm 2 elect 2! 7

29 Bully Algorithm 2 elect 2? elect! 8

30 Bully Algorithm 2 elect 2? inaug 9

31 Bully Algorithm 2 50

32 Bully Algorithm

33 Bully Algorithm 1 2 elect 1! 52

34 Bully Algorithm 1 2 elect 1? elect 2! 5

35 Bully Algorithm 1 2 elect 1? elect 2? elect! 5

36 Bully Algorithm

37 Bully Algorithm

38 Bully Algorithm 1 2 elect! 57

39 Bully Algorithm 1 2 inaug 58

40 Bully Algorithm

41 Ring Algorithm When communication is always to the next live site If a process i doesn t hear back from a coordinator: Send an elect message to neighbor Accumulate elect messages to learn about live sites Get own elect all sites known 60

42 Ring Algorithm

43 Ring Algorithm

44 Ring Algorithm 2 6

45 Ring Algorithm 2 wait on 6

46 Ring Algorithm 2 [2,...] elect(2) 65

47 Ring Algorithm 2 [2] [2,,...] elect() elect(2) 66

48 Ring Algorithm 2 [2,,...] elect() [2,,...] elect(2) 67

49 Ring Algorithm 2 [2,] elect() [2,,...] 68

50 Ring Algorithm 2 [2,] [2,] 69

51 Ring Algorithm 2 70

52 Multi-Site Atomicity 71

53 Multi-Site Atomicity <buyer image> <seller image> <bank image> 72

54 Two-Phase Commit <buyer image> <seller image> <bank image> 7

55 Two-Phase Commit <buyer image> <seller image> <bank image> 7

56 Two-Phase Commit <buyer image> <seller image> <bank image> transfer money 75

57 Two-Phase Commit <buyer image> <seller image> give keys <bank image> transfer money 76

58 Two-Phase Commit <buyer image> <seller image> take keys give keys <bank image> transfer money 77

59 Two-Phase Commit <buyer image> <seller image> take keys give keys 78

60 Two-Phase Commit <buyer image> <seller image> take keys give keys <bank image> transfer money 79

61 Two-Phase Commit <buyer image> <seller image> take keys <prepare> give keys <bank image> transfer money 80

62 Two-Phase Commit <buyer image> <seller image> take keys <prepare> give keys <ready> <bank image> transfer money 81

63 Two-Phase Commit <buyer image> <seller image> take keys <prepare> give keys <ready> 82

64 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <fail> give keys <ready> 8

65 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <fail> give keys <ready> <fail> 8

66 Two-Phase Commit <buyer image> <seller image> take keys <prepare> give keys <ready> <bank image> transfer money 85

67 Two-Phase Commit <buyer image> <seller image> take keys <prepare> give keys <ready> <bank image> transfer money <ready> 86

68 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <commit> give keys <ready> <bank image> transfer money <ready> 87

69 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <commit> give keys <ready> <commit> <bank image> transfer money <ready> 88

70 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <commit> give keys <ready> <commit> transfer money <ready> 89

71 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <commit> give keys <ready> <commit> <bank image> transfer money <ready> 90

72 Two-Phase Commit <buyer image> <seller image> take keys <prepare> <commit> give keys <ready> <commit> <bank image> transfer money <ready> <commit> 91

73 Things You Can t Do Two-way common knowledge e.g., buyers commit only if they know that the bank received the message to finalize the transaction Handle too many byzantine failures Can use voting to detect when up to 1/ of the sites are faulty, but not when more are faulty 92