Chord: A Scalable Peer-to-peer Lookup Service for Internet Applications

90-minute presentation for the Advanced topics in Data Management course at KAUST, on "A Scalable Peer-to-peer Lookup Service for Internet Applications" by Stoica et al, published in SIGCOMM '01.

Transcript

1. Chord Stoica et al., SIGCOMM '01 May 4, 2014 | Emaad Ahmed Manzoor CS341: Advanced Topics in Data Management
2. Problem Motivation & metrics Solution The Chord Protocol Protocol Analysis Provable guarantees Experimental Results Simulations May 4, 2014 | Emaad Ahmed Manzoor
3. Problem Motivation & metrics Solution The Chord Protocol Protocol Analysis Provable guarantees Experimental Results Simulations May 4, 2014 | Emaad Ahmed Manzoor
4. May 4, 2014 | Emaad Ahmed Manzoor
5. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value
6. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value
7. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Keys are distributed across decentralized nodes
8. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Keys are distributed across decentralized nodes
9. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Nodes may arrive or leave at any time Keys are distributed across decentralized nodes
10. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value
11. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value
12. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Routing Tables
13. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Communication Cost Routing Tables
14. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Communication Cost Routing Tables Maintenance Cost
15. May 4, 2014 | Emaad Ahmed Manzoor Map a key to a node in the network containing the corresponding value Communication Cost Routing Tables Scalability f(N) Maintenance Cost
16. May 4, 2014 | Emaad Ahmed Manzoor Keys are distributed across decentralized nodes
17. May 4, 2014 | Emaad Ahmed Manzoor Keys are distributed across decentralized nodes
18. May 4, 2014 | Emaad Ahmed Manzoor Keys are distributed across decentralized nodes Load Balance f (|k|/N)
19. May 4, 2014 | Emaad Ahmed Manzoor Keys are distributed across decentralized nodes Load Balance f (|k|/N)
20. May 4, 2014 | Emaad Ahmed Manzoor Keys are distributed across decentralized nodes Load Balance f (|k|/N) Asynchronous
21. May 4, 2014 | Emaad Ahmed Manzoor Nodes may arrive or leave at any time
22. May 4, 2014 | Emaad Ahmed Manzoor Nodes may arrive or leave at any time Availability
23. May 4, 2014 | Emaad Ahmed Manzoor Nodes may arrive or leave at any time Availability + Asynchronous
24. May 4, 2014 | Emaad Ahmed Manzoor Nodes may arrive or leave at any time Availability + Asynchronous = Correctness
25. May 4, 2014 | Emaad Ahmed Manzoor Scalability Load Balance Availability Asynchronous Correctness Map a key to a node in the network containing the corresponding value Keys are distributed across decentralized nodes Nodes may arrive or leave at any time
26. Problem Motivation & metrics Solution The Chord Protocol Protocol Analysis Provable guarantees Experimental Results Simulations May 4, 2014 | Emaad Ahmed Manzoor
27. May 4, 2014 | Emaad Ahmed Manzoor N N N N N N Internet
28. May 4, 2014 | Emaad Ahmed Manzoor N N N N N N Internet Publisher key = k value = v
29. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Client key = k value = ?
30. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Client key = k value = ? Assignment Load Balancing Asynchronous
31. May 4, 2014 | Emaad Ahmed Manzoor Consistent Hashing Distribute keys across nodes
32. May 4, 2014 | Emaad Ahmed Manzoor Consistent Hashing key_identifier = hash(key) = 110001 m bits, m = 6
33. May 4, 2014 | Emaad Ahmed Manzoor Consistent Hashing key_identifier = hash(key) = 110001 node_identifier = hash(node IP) = 100101 m bits, m = 6
34. May 4, 2014 | Emaad Ahmed Manzoor Consistent Hashing key_identifier = hash(key) = 110001 node_identifier = hash(node IP) = 100101 m bits, m = 6 Identifier ring identifier % 2m = 0 to 63
35. May 4, 2014 | Emaad Ahmed Manzoor Consistent Hashing key_identifier = hash(key) = 110001 node_identifier = hash(node IP) = 100101 m bits, m = 6 Node for k successor(key_identifer) Identifier ring identifier % 2m = 0 to 63
36. May 4, 2014 | Emaad Ahmed Manzoor Load Balancing with Consistent Hashing N nodes, K keys, with high probability: - Each node has at most (1 + e)K/N keys - On arrival or departure of a node, O(K/N) keys exchange hands
37. May 4, 2014 | Emaad Ahmed Manzoor Load Balancing with Consistent Hashing (a) N = 10,000 (b) k = 500,000
38. May 4, 2014 | Emaad Ahmed Manzoor Load Balancing with Consistent Hashing (a) N = 10,000 (b) k = 500,000 Large variation in the number of keys per node
39. May 4, 2014 | Emaad Ahmed Manzoor Load Balancing with Consistent Hashing (a) N = 10,000 (b) k = 500,000 Many nodes have no keys
40. May 4, 2014 | Emaad Ahmed Manzoor Reason for The Load Imbalance
41. May 4, 2014 | Emaad Ahmed Manzoor Reason for The Load Imbalance Node identifiers do not uniformly cover the identifier space
42. May 4, 2014 | Emaad Ahmed Manzoor Reason for The Load Imbalance Node identifiers do not uniformly cover the identifier space Solution Virtual Nodes
43. May 4, 2014 | Emaad Ahmed Manzoor Load Balance with Virtual Nodes
44. May 4, 2014 | Emaad Ahmed Manzoor Load Balance with Virtual Nodes Load balance improves with more virtual nodes per real node
45. May 4, 2014 | Emaad Ahmed Manzoor Load Balance with Virtual Nodes Load balance improves with more virtual nodes per real node Cost of routing information per node also increases
46. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Client key = k value = ? Assignment Load Balancing Asynchronous
47. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Client key = k value = ? Lookup Scalability Asynchronous Assignment Load Balancing Asynchronous
48. May 4, 2014 | Emaad Ahmed Manzoor
49. May 4, 2014 | Emaad Ahmed Manzoor Routing information: O(1) Communication: O(N)
50. May 4, 2014 | Emaad Ahmed Manzoor
51. May 4, 2014 | Emaad Ahmed Manzoor m entries
52. May 4, 2014 | Emaad Ahmed Manzoor m entries
53. May 4, 2014 | Emaad Ahmed Manzoor Routing information: log(N)
54. May 4, 2014 | Emaad Ahmed Manzoor Communication cost: ?
55. May 4, 2014 | Emaad Ahmed Manzoor Each node can forward a request at most halfway around the identifier circle
56. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = ?
57. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = ?
58. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = ? 0000 1000 1011
59. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = ? 0000 1000 1011 d 0 = 1011
60. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = ? 0000 1000 1011 d 1 = 0011
61. May 4, 2014 | Emaad Ahmed Manzoor Expected number of query steps if node n wants to find the predecessor p of key k = 0.5 x log(N)
62. May 4, 2014 | Emaad Ahmed Manzoor Routing information: O(log(N)) Communication cost: O(log(N))
63. May 4, 2014 | Emaad Ahmed Manzoor Lookup Cost in Practice 212 node network
64. May 4, 2014 | Emaad Ahmed Manzoor Lookup Cost in Practice Path length = query steps. Grows as log(N) 212 node network
65. May 4, 2014 | Emaad Ahmed Manzoor Lookup Cost in Practice Path length = query steps. Grows as log(N) Mean path length = 0.5 x log(N) 212 node network
66. May 4, 2014 | Emaad Ahmed Manzoor Lookup Cost in Practice Path length = query steps. Grows as log(N) Mean path length = 0.5 x log(N) High variance in path length?
67. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Lookup Scalability Asynchronous Assignment Load Balancing Asynchronous Client key = k value = ?
68. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Lookup Scalability Asynchronous Assignment Load Balancing Asynchronous Client key = k value = ?
69. May 4, 2014 | Emaad Ahmed Manzoor Publisher key = k value = v N N N N N N Internet Lookup Scalability Asynchronous Assignment Load Balancing Asynchronous Client key = k value = ? Joins/Failure Availability Correctness Scalability
70. May 4, 2014 | Emaad Ahmed Manzoor
71. May 4, 2014 | Emaad Ahmed Manzoor
72. May 4, 2014 | Emaad Ahmed Manzoor
73. May 4, 2014 | Emaad Ahmed Manzoor Stabilize protocol - Stabilize Updates successors - Notify Updates predecessors - Fix fingers Updates finger tables
74. May 4, 2014 | Emaad Ahmed Manzoor
75. May 4, 2014 | Emaad Ahmed Manzoor What if a lookup happens now?
76. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, successors are correct
77. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result
78. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, successors are correct
79. May 4, 2014 | Emaad Ahmed Manzoor 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, O(N) lookup cost successors are correct Correctness of Lookups with Node Joins
80. May 4, 2014 | Emaad Ahmed Manzoor 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, O(N) lookup cost successors are correct Correct lookup result Correctness of Lookups with Node Joins
81. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, O(N) lookup cost successors are correct Correct lookup result - Successors are incorrect
82. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, O(N) lookup cost successors are correct Correct lookup result - Successors are incorrect Lookup fails
83. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Joins 3 cases - Finger table entries are current, O(log(N)) lookup cost successors are correct Correct lookup result - Finger table entries are stale, O(N) lookup cost successors are correct Correct lookup result - Successors are incorrect Lookup fails Application layer pauses and retries failed lookups
84. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Joins
85. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Joins With high probability, O (log(N)) new nodes will land between any two existing nodes
86. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Joins With high probability, O (log(N)) new nodes will land between any two existing nodes Lookups remain O(log(N))
87. May 4, 2014 | Emaad Ahmed Manzoor Node Failure
88. May 4, 2014 | Emaad Ahmed Manzoor Node Failure
89. May 4, 2014 | Emaad Ahmed Manzoor Node Failure Each node maintains a successor list of size r
90. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Failure Mean path length with successor lists = 0.5 x log(N) - 0.5 x log(r) + 1
91. May 4, 2014 | Emaad Ahmed Manzoor Correctness of Lookups with Node Failure
92. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Failure Mean path length with successor lists = 0.5 x log(N) - 0.5 x log(r) + 1 Eliminates the last 0.5 x log(r) hops on average
93. May 4, 2014 | Emaad Ahmed Manzoor Performance of Lookups with Node Failure Mean path length with successor lists = 0.5 x log(N) - 0.5 x log(r) + 1 Access the predecessor of the key k from the node n' retrieved from the successor list
94. May 4, 2014 | Emaad Ahmed Manzoor Scalability Load Balance Availability Asynchronous Correctness Map a key to a node in the network containing the corresponding value Keys are distributed across decentralized nodes Nodes may arrive or leave at any time Chord
95. May 4, 2014 | Emaad Ahmed Manzoor .