Coordination-Free Designs for Mobile Gaming

Code Mesh 2015, September 3rd, 2015

Transcript

1. Coordination-Free Designs
   
   for Mobile Gaming
   Christopher Meiklejohn // @cmeik
   Code Mesh 2015, September 3rd, 2015
   1
   

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2. RA
   RB
   

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3. RA
   RB
   1
   set(1)
   

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4. RA
   RB
   1
   set(1)
   3
   2
   set(2)
   set(3)
   

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5. RA
   RB
   1
   set(1)
   3
   2
   set(2)
   set(3)
   ?
   ?
   

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6. Synchronization
   • To enforce an order

   Makes programming easier
   6
   

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7. Synchronization
   • To enforce an order

   Makes programming easier
   • Eliminate accidental nondeterminism

   Prevent race conditions
   6
   

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8. Synchronization
   • To enforce an order

   Makes programming easier
   • Eliminate accidental nondeterminism

   Prevent race conditions
   • Techniques

   Locks, mutexes, semaphores, monitors, etc.
   6
   

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9. Difficult Cases
   • “Internet of Things”

   Low power, limited memory and connectivity
   7
   

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10. Difficult Cases
    • “Internet of Things”

    Low power, limited memory and connectivity
    • Mobile Gaming

    Offline operation with replicated, shared state
    7
    

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11. Zero Synchronization
    • We want to have our cake and eat it too.
    8
    

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12. Zero Synchronization
    • We want to have our cake and eat it too.
    • “Zero synchronization” as a starting point

    Add synchronization only where it is necessary
    8
    

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13. Zero Synchronization
    • We want to have our cake and eat it too.
    • “Zero synchronization” as a starting point

    Add synchronization only where it is necessary
    • Explore the limits

    Can we design a model of computation where it’s
    easy to write coordination-free computations that
    are free from concurrency anomalies?
    8
    

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14. The Fundamentals of
    Distributed Computation
    9
    

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15. Distributed Computation
    • Distributed to concurrent programming

    Consistency and now partial failure
    10
    

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16. Distributed Computation
    • Distributed to concurrent programming

    Consistency and now partial failure
    • Enforcing the “single system” illusion
    10
    

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17. Distributed Computation
    • Distributed to concurrent programming

    Consistency and now partial failure
    • Enforcing the “single system” illusion
    • Consistency model as a contract
    10
    

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18. Distributed Computation
    • Distributed to concurrent programming

    Consistency and now partial failure
    • Enforcing the “single system” illusion
    • Consistency model as a contract
    • Enforced through synchronization
    10
    

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19. Distributed Computation
    • Distributed to concurrent programming

    Consistency and now partial failure
    • Enforcing the “single system” illusion
    • Consistency model as a contract
    • Enforced through synchronization
    • Consistency model

    We can think of a consistency model as analogous
    to a programming paradigm
    10
    

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20. Why Is Synchronization
    Undesirable?
    11
    

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21. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    12
    

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22. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    • Time has three major avatars in computing
    12
    

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23. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    • Time has three major avatars in computing
    • Mutable state in sequential systems
    12
    

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24. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    • Time has three major avatars in computing
    • Mutable state in sequential systems
    • Nondeterminism in concurrent systems
    12
    

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25. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    • Time has three major avatars in computing
    • Mutable state in sequential systems
    • Nondeterminism in concurrent systems
    ̣ Network latency in distributed systems
    12
    

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26. The Avatars of Time
    • The problem of time

    Handling physical time in applications is difficult
    • Time has three major avatars in computing
    • Mutable state in sequential systems
    • Nondeterminism in concurrent systems
    ̣ Network latency in distributed systems
    • Unavoidable

    Time is how users interact with programs
    12
    

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27. Parable of the Car
    • “Car driving on a highway”
    13
    

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28. Parable of the Car
    • “Car driving on a highway”
    • Friction needed for the car to grip the road
    13
    

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29. Parable of the Car
    • “Car driving on a highway”
    • Friction needed for the car to grip the road
    • Motors want as little friction as possible
    13
    

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30. Parable of the Car
    • “Car driving on a highway”
    • Friction needed for the car to grip the road
    • Motors want as little friction as possible
    • Time is like friction

    We can not completely eliminate friction, but aim to
    reduce it as much as possible
    13
    

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31. Physical
    Time
    (real world)
    Parable of the Car
    14
    • Time only at the interface

    The interface is a small part of the system, and this is where we
    introduction friction
    

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32. Physical
    Time
    (real world)
    Parable of the Car
    14
    • Time only at the interface

    The interface is a small part of the system, and this is where we
    introduction friction
    • Physical time-free execution

    Internally, avoid synchronization as much as possible and virtualize
    notion of time
    

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33. No Time In The Box?
    15
    

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34. No Time In The Box?
    15
    You program the box.
    

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35. Weak Synchronization
    • Can we achieve anything without synchronization?

    Not really.
    16
    

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36. Weak Synchronization
    • Can we achieve anything without synchronization?

    Not really.
    • Strong Eventual Consistency (SEC)

    “Replicas that deliver the same updates have equivalent state”
    16
    

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37. Weak Synchronization
    • Can we achieve anything without synchronization?

    Not really.
    • Strong Eventual Consistency (SEC)

    “Replicas that deliver the same updates have equivalent state”
    • Primary requirement

    Eventual replica-to-replica communication
    16
    

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38. Weak Synchronization
    • Can we achieve anything without synchronization?

    Not really.
    • Strong Eventual Consistency (SEC)

    “Replicas that deliver the same updates have equivalent state”
    • Primary requirement

    Eventual replica-to-replica communication
    • Order insensitive! (Commutativity)
    16
    

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39. Weak Synchronization
    • Can we achieve anything without synchronization?

    Not really.
    • Strong Eventual Consistency (SEC)

    “Replicas that deliver the same updates have equivalent state”
    • Primary requirement

    Eventual replica-to-replica communication
    • Order insensitive! (Commutativity)
    • Duplicate insensitive! (Idempotent)
    16
    

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40. RA
    RB
    

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41. RA
    RB
    1
    set(1)
    

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42. RA
    RB
    1
    set(1)
    3
    2
    set(2)
    set(3)
    

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43. RA
    RB
    1
    3
    2
    3
    3
    set(1) set(2)
    set(3)
    max(2,3)
    max(2,3)
    

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44. How can we succeed with
    Strong Eventual Consistency?
    21
    

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45. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    22
    

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46. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    22
    

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47. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    3. Distributed, and fault-tolerant runtime

    (ex. replication)
    22
    

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48. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    3. Distributed, and fault-tolerant runtime

    (ex. replication)
    23
    

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49. Convergent Objects

    Conflict-Free 

    Replicated Data Types
    24
    SSS 2011
    

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50. Conflict-Free 

    Replicated Data Types
    • Many types exist with different properties

    Sets, counters, registers, flags, maps, graphs
    25
    

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51. Conflict-Free 

    Replicated Data Types
    • Many types exist with different properties

    Sets, counters, registers, flags, maps, graphs
    • Strong Eventual Consistency

    Instances satisfy SEC property per-object
    25
    

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52. RA
    RB
    RC
    

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53. RA
    RB
    RC
    {1}
    (1, {a}, {})
    add(1)
    

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54. RA
    RB
    RC
    {1}
    (1, {a}, {})
    add(1)
    {1}
    (1, {c}, {})
    add(1)
    

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55. RA
    RB
    RC
    {1}
    (1, {a}, {})
    add(1)
    {1}
    (1, {c}, {})
    add(1)
    {}
    (1, {c}, {c})
    remove(1)
    

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56. RA
    RB
    RC
    {1}
    (1, {a}, {})
    add(1)
    {1}
    (1, {c}, {})
    add(1)
    {}
    (1, {c}, {c})
    remove(1)
    {1}
    {1}
    {1}
    (1, {a, c}, {c})
    (1, {a, c}, {c})
    (1, {a, c}, {c})
    

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57. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    3. Distributed, and fault-tolerant runtime

    (ex. replication)
    31
    

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58. Convergent Programs
    Lattice Processing
    32
    PPDP 2015
    

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59. Lattice Processing (Lasp)
    • Distributed, deterministic dataflow

    Distributed, deterministic dataflow programming
    model for “eventually consistent” computations
    33
    

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60. Lattice Processing (Lasp)
    • Distributed, deterministic dataflow

    Distributed, deterministic dataflow programming
    model for “eventually consistent” computations
    • Convergent data structures

    Primary data abstraction is the CRDT
    33
    

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61. Lattice Processing (Lasp)
    • Distributed, deterministic dataflow

    Distributed, deterministic dataflow programming
    model for “eventually consistent” computations
    • Convergent data structures

    Primary data abstraction is the CRDT
    • Enables composition

    Provides functional composition of CRDTs that
    preserves the SEC property
    33
    

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62. 34
    %% Create initial set.
    S1 = declare(set),
    %% Add elements to initial set and update.
    update(S1, {add, [1,2,3]}),
    %% Create second set.
    S2 = declare(set),
    %% Apply map operation between S1 and S2.
    map(S1, fun(X) -> X * 2 end, S2).
    

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63. 35
    %% Create initial set.
    S1 = declare(set),
    %% Add elements to initial set and update.
    update(S1, {add, [1,2,3]}),
    %% Create second set.
    S2 = declare(set),
    %% Apply map operation between S1 and S2.
    map(S1, fun(X) -> X * 2 end, S2).
    

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64. 36
    %% Create initial set.
    S1 = declare(set),
    %% Add elements to initial set and update.
    update(S1, {add, [1,2,3]}),
    %% Create second set.
    S2 = declare(set),
    %% Apply map operation between S1 and S2.
    map(S1, fun(X) -> X * 2 end, S2).
    

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65. 37
    %% Create initial set.
    S1 = declare(set),
    %% Add elements to initial set and update.
    update(S1, {add, [1,2,3]}),
    %% Create second set.
    S2 = declare(set),
    %% Apply map operation between S1 and S2.
    map(S1, fun(X) -> X * 2 end, S2).
    

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66. 38
    %% Create initial set.
    S1 = declare(set),
    %% Add elements to initial set and update.
    update(S1, {add, [1,2,3]}),
    %% Create second set.
    S2 = declare(set),
    %% Apply map operation between S1 and S2.
    map(S1, fun(X) -> X * 2 end, S2).
    

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67. Lattice Processing (Lasp)
    • Functional and set-theoretic operations on sets

    Product, intersection, union, filter, map, fold
    39
    

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68. Lattice Processing (Lasp)
    • Functional and set-theoretic operations on sets

    Product, intersection, union, filter, map, fold
    • Metadata computation

    Performs transformation on the internal metadata of
    CRDTs allowing creation of “composed” CRDTs
    39
    

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69. Lasp Processes
    • Replicas as monotonic streams

    Each replica of a CRDT produces a monotonic
    stream of states
    40
    

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70. Lasp Processes
    • Replicas as monotonic streams

    Each replica of a CRDT produces a monotonic
    stream of states
    • Monotonic processes

    Read from one or more input replica streams and
    produce a single output replica stream
    40
    

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71. Lasp Processes
    • Replicas as monotonic streams

    Each replica of a CRDT produces a monotonic
    stream of states
    • Monotonic processes

    Read from one or more input replica streams and
    produce a single output replica stream
    • Inflationary reads

    Read operation ensures that we only read
    inflationary updates to replicas
    40
    

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72. Lattice Processing
    Monotonic Streams
    41
    

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73. RA
    {}
    C1
    {}
    C2
    {}
    42
    

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74. RA
    {}
    (1, {a}, {})
    C1
    (1, {a}, {})
    {}
    C2
    {}
    43
    

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75. RA
    {}
    (1, {a}, {})
    (1, {a, c}, {})
    C1
    (1, {a}, {})
    {}
    C2
    (1, {c}, {})
    {}
    44
    

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76. RA
    {}
    (1, {a}, {})
    (1, {a, c}, {})
    (1, {a, c}, {a})
    C1
    (1, {a}, {})
    {}
    (1, {a}, {a})
    C2
    (1, {c}, {})
    {}
    45
    

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77. RA
    {}
    (1, {a}, {})
    (1, {a, c}, {})
    (1, {a, c}, {a})
    C1
    (1, {a}, {})
    {}
    (1, {a}, {a})
    C2
    (1, {c}, {})
    {}
    (1, {a, c}, {a})
    (1, {a, c}, {a}) (1, {a, c}, {a})
    46
    

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78. RA
    {}
    (1, {a}, {})
    (1, {a, c}, {})
    (1, {a, c}, {a})
    C1
    (1, {a}, {})
    {}
    (1, {a}, {a})
    C2
    (1, {c}, {})
    {}
    (1, {a, c}, {a})
    (1, {a, c}, {a}) (1, {a, c}, {a})
    47
    

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79. Lattice Processing
    Monotonic Processes
    48
    

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80. RA
    {}
    P1 F(RA)
    {}
    49
    

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81. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    50
    

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82. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {})
    51
    

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83. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {}) F((1, {a}, {}))
    52
    

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84. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {}) F((1, {a}, {})) (2, {a}, {})
    53
    

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85. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {}) F((1, {a}, {})) (2, {a}, {})
    strict_read((1, {a}, {})
    (1, {a}, {})
    54
    

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86. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {}) F((1, {a}, {})) (2, {a}, {})
    strict_read((1, {a}, {})
    (1, {a}, {})
    (1, {a}, {a}) F((1, {a}, {a})) (2, {a}, {a})
    strict_read((1, {a}, {a})
    (1, {a}, {a})
    55
    

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87. RA
    {}
    P1 F(RA)
    {}
    strict_read({})
    (1, {a}, {})
    (1, {a}, {})
    (1, {a}, {a}) F((1, {a}, {a})) (2, {a}, {a})
    strict_read((1, {a}, {a})
    (1, {a}, {a})
    56
    

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88. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    3. Distributed, and fault-tolerant runtime

    (ex. replication)
    57
    

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89. Distributed Runtime
    Selective Hearing
    58
    W-PSDS 2015
    

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90. Selective Hearing
    • Epidemic broadcast based runtime system

    Provide a runtime system that can scale to large numbers of
    nodes, that is resilient to failures and provides efficient execution
    59
    

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91. Selective Hearing
    • Epidemic broadcast based runtime system

    Provide a runtime system that can scale to large numbers of
    nodes, that is resilient to failures and provides efficient execution
    • Well-matched to Lattice Processing (Lasp)
    59
    

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92. Selective Hearing
    • Epidemic broadcast based runtime system

    Provide a runtime system that can scale to large numbers of
    nodes, that is resilient to failures and provides efficient execution
    • Well-matched to Lattice Processing (Lasp)
    • Epidemic broadcast mechanisms provide weak ordering but
    are resilient and efficient
    59
    

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93. Selective Hearing
    • Epidemic broadcast based runtime system

    Provide a runtime system that can scale to large numbers of
    nodes, that is resilient to failures and provides efficient execution
    • Well-matched to Lattice Processing (Lasp)
    • Epidemic broadcast mechanisms provide weak ordering but
    are resilient and efficient
    • Lasp’s programming model is tolerant to message re-ordering,
    disconnections, and node failures
    59
    

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94. Selective Hearing
    • Epidemic broadcast based runtime system

    Provide a runtime system that can scale to large numbers of
    nodes, that is resilient to failures and provides efficient execution
    • Well-matched to Lattice Processing (Lasp)
    • Epidemic broadcast mechanisms provide weak ordering but
    are resilient and efficient
    • Lasp’s programming model is tolerant to message re-ordering,
    disconnections, and node failures
    • “Selective Receive”

    Nodes selectively receive and process messages based on
    interest
    59
    

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95. Programming SEC
    1. Eliminate accidental nondeterminism

    (ex. deterministic, modeling non-monotonic operations monotonically)
    
    2. Retain the properties of functional programming

    (ex. confluence, referential transparency over composition)
    3. Distributed, and fault-tolerant runtime

    (ex. replication)
    60
    

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96. What can we build?
    Leaderboard
    61
    

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97. Leaderboard
    • Mobile game platform

    Local leaderboard tracking top-k highest scored
    games
    62
    

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98. Leaderboard
    • Mobile game platform

    Local leaderboard tracking top-k highest scored
    games
    • Clients will go offline

    Clients have limited connectivity and the system still
    needs to make progress while clients are offline
    62
    

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99. Client 1
    Leaderboard
    Client 3
    Leaderboard
    Client 2
    Leaderboard
    Lasp Operation
    User-Maintained CRDT
    Lasp-Maintained CRDT
    63
    

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100. Leaderboard
     • Peer-to-peer dissemination

     Nodes periodically “merge” their state with a
     random peer
     64
     

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101. Leaderboard
     • Peer-to-peer dissemination

     Nodes periodically “merge” their state with a
     random peer
     • Complexity in the data type

     Each node tracks a top-k set of its own games in a
     bounded set
     64
     

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102. 65
     %% Create a leaderboard datatype.
     L = declare({top_k, [2]}).
     %% Update leaderboard.
     update({set, Name, Score}, L).
     

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103. 66
     %% Create a leaderboard datatype.
     L = declare({top_k, [2]}).
     %% Update leaderboard.
     update({set, Name, Score}, L).
     

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104. 67
     %% Create a leaderboard datatype.
     L = declare({top_k, [2]}).
     %% Update leaderboard.
     update({set, Name, Score}, L).
     

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105. What if we want to enhance
     the behavior?
     68
     

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106. What if we want to enhance
     the behavior?
     68
     Without the creation of a
     new datatype
     

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107. What can we build?
     Per-User Leaderboard
     69
     EdgeCom 2016
     

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108. Per-User Leaderboard
     • Enhance existing design

     Only the top score for each user at each device
     70
     

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109. Per-User Leaderboard
     • Enhance existing design

     Only the top score for each user at each device
     • Minimize transmitted state

     Prevent transmission of state that is not necessary
     to perform the computation
     70
     

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110. Per-User Leaderboard
     • Enhance existing design

     Only the top score for each user at each device
     • Minimize transmitted state

     Prevent transmission of state that is not necessary
     to perform the computation
     • Compose data types

     Build a per-user leaderboard through the
     composition of existing types
     70
     

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111. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Lasp Operation
     Input
     User-Maintained CRDT
     Output
     Lasp-Maintained CRDT Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     71
     

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112. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     72
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

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113. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     73
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

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114. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     74
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

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115. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     75
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

     View Slide

116. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     76
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

     View Slide

117. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     77
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

     View Slide

118. Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Lasp Operation
     Input
     User-Maintained CRDT
     Output
     Lasp-Maintained CRDT Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     78
     Client1
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client3
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     Client2
     Scores
     Local
     Top-K
     Fold
     Global
     Top-K
     Fold
     

     View Slide

119. Per-User Leaderboard
     • Dynamically scoped variables

     Variable which take different values depending on
     where it is executing
     79
     

     View Slide

120. Per-User Leaderboard
     • Dynamically scoped variables

     Variable which take different values depending on
     where it is executing
     • Dynamically scoped fold operation

     Perform a distributed “reduce” operation that
     combines the state of a dynamically scoped
     variables across
     79
     

     View Slide

121. 80
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

122. 81
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

123. 82
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

124. 83
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

125. 84
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

126. 85
     %% Create a global leaderboard.
     G = declare({top_k, [10]}).
     %% Create a local leaderboard.
     L = declare_dynamic({top_k, [10]}).
     %% Create a set of scores.
     S = declare_dynamic(set).
     %% Compute local top-k list.
     fold(S, fun max_by_name/2, L).
     %% Compute global top-k list.
     fold_dynamic(L, fun max_by_name/2, G).
     

     View Slide

127. Let’s look at a larger
     application
     86
     

     View Slide

128. Let’s look at a larger
     application
     86
     With visible 

     non-monotonicity
     

     View Slide

129. What can we build?
     Advertisement Counter
     87
     

     View Slide

130. Advertisement Counter
     • Mobile game platform selling advertisement space

     Advertisements are paid according to a minimum
     number of impressions
     88
     

     View Slide

131. Advertisement Counter
     • Mobile game platform selling advertisement space

     Advertisements are paid according to a minimum
     number of impressions
     • Clients will go offline

     Clients have limited connectivity and the system still
     needs to make progress while clients are offline
     88
     

     View Slide

132. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     89
     

     View Slide

133. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Riot Ads
     Rovio
     Ads
     Product
     Read
     50,000
     Remove
     Increment
     Union
     90
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

134. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Client
     91
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

135. Ads
     ovio Ad
     ounter 1
     ovio Ad
     ounter 2
     iot Ad
     ounter 1
     iot Ad
     ounter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Rovio Ad
     Counter
     1
     Ro
     C
     Rovio Ad
     Counter
     1
     Ro
     C
     Rovio Ad
     Counter
     1
     Ro
     C
     Rovio Ad
     Counter
     1
     Ro
     C
     Client Side, Sing
     92
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

136. Ads
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     move Read
     Union
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     93
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

137. Ads
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Filter
     Product
     Read
     Union
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     94
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

138. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     95
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

139. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Riot Ads
     Rovio
     Ads
     Fil
     Product
     Read
     50,000
     Remove
     Increment
     Union
     96
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

140. Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     97
     Ads
     Rovio Ad
     Counter 1
     Rovio Ad
     Counter 2
     Riot Ad
     Counter 1
     Riot Ad
     Counter 2
     Contracts
     Ads
     Contracts
     Ads
     With
     Contracts
     Riot Ads
     Rovio
     Ads
     Filter
     Product
     Read
     50,000
     Remove
     Increment
     Read
     Union
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Client Side, Single Copy at Client
     

     View Slide

141. Advertisement Counter
     • Completely monotonic

     Disabling advertisements and contracts are all
     modeled through monotonic state growth
     98
     

     View Slide

142. Advertisement Counter
     • Completely monotonic

     Disabling advertisements and contracts are all
     modeled through monotonic state growth
     • Arbitrary distribution

     Use of convergent data structures allows
     computational graph to be arbitrarily distributed
     98
     

     View Slide

143. Advertisement Counter
     • Completely monotonic

     Disabling advertisements and contracts are all
     modeled through monotonic state growth
     • Arbitrary distribution

     Use of convergent data structures allows
     computational graph to be arbitrarily distributed
     • Divergence

     Divergence is a factor of synchronization period
     98
     

     View Slide

144. 99
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

     View Slide

145. 100
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

     View Slide

146. 101
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

     View Slide

147. 102
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

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148. 103
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

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149. 104
     %% Generate a series of contracts.
     Contracts = declare(set),
     %% Generate advertisements.
     RiotAds = declare(set),
     RovioAds = declare(set),
     create_advertisements_and_contracts(RiotAds, Contracts),
     create_advertisements_and_contracts(RovioAds, Contracts),
     %% Union ads.
     Ads = declare(set),
     union(RovioAds, RiotAds, Ads),
     %% Compute the product of both ads and contracts.
     AdsContracts = declare(set),
     product(Ads, Contracts, AdsContracts),
     %% Filter items by join on item it.
     AdsWithContracts = declare(set),
     FilterFun = fun({#ad{id=Id1}, #contract{id=Id2}}) ->
     Id1 =:= Id2
     end,
     filter(AdsContracts, FilterFun, AdsWithContracts).
     

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150. Client3
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Riot Ad
     Counter
     1
     Client1
     Client2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Riot Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Riot Ad
     Counter
     1
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Server
     Ads
     With
     Contracts
     Server
     Computation!
     105
     

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151. Client3
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Riot Ad
     Counter
     1
     Client1
     Client2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Riot Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Riot Ad
     Counter
     1
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Server
     Ads
     With
     Contracts
     Server
     Computation!
     106
     

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152. Client3
     Lasp Operation
     User-Maintained CRDT
     Lasp-Maintained CRDT
     Riot Ad
     Counter
     1
     Client1
     Client2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Rovio Ad
     Counter
     2
     Rovio Ad
     Counter
     1
     Riot Ad
     Counter
     2
     Riot Ad
     Counter
     1
     Riot Ad
     Counter
     1
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Ads
     With
     Contracts
     Server
     Ads
     With
     Contracts
     Server
     Computation!
     107
     

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153. Advertisement Counter
     • “Servers” as peers to “clients”

     Servers are peers to clients that perform additional
     computation
     108
     

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154. Advertisement Counter
     • “Servers” as peers to “clients”

     Servers are peers to clients that perform additional
     computation
     • Any node can disable an advertisement under this
     model given enough information
     108
     

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155. Advertisement Counter
     • “Servers” as peers to “clients”

     Servers are peers to clients that perform additional
     computation
     • Any node can disable an advertisement under this
     model given enough information
     • “Servers” as trusted nodes

     Serve as a location for performing “exactly once” side-
     effects
     108
     

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156. Advertisement Counter
     • “Servers” as peers to “clients”

     Servers are peers to clients that perform additional
     computation
     • Any node can disable an advertisement under this
     model given enough information
     • “Servers” as trusted nodes

     Serve as a location for performing “exactly once” side-
     effects
     • Billing customers must be done at a central point by a
     trusted node in the system
     108
     

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157. We’ve build up from zero
     synchronization
     109
     

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158. We’ve build up from zero
     synchronization
     109
     Instead of working to
     remove synchronization
     

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159. What have we learned?
     110
     

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160. Key Points
     • Synchronization is expensive

     Locking and other synchronization mechanisms limit
     scalability to the critical section
     111
     

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161. Key Points
     • Synchronization is expensive

     Locking and other synchronization mechanisms limit
     scalability to the critical section
     • Synchronization is sometimes not possible

     Mobile and “Internet of Things” applications make
     synchronization for replicated state impractical
     111
     

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162. Key Points
     • Synchronization is expensive

     Locking and other synchronization mechanisms limit
     scalability to the critical section
     • Synchronization is sometimes not possible

     Mobile and “Internet of Things” applications make
     synchronization for replicated state impractical
     • Apply synchronization only where required

     Global invariants, atomic visibility, etc.
     111
     

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163. How do I learn more?
     112
     

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164. Publications
     • “Lasp: A Language for Distributed, Coordination-Free Programming” 

     ACM SIGPLAN PPDP 2015
     
     • “Selective Hearing: An Approach to Distributed, Eventually Consistent Edge Computation”

     IEEE W-PSDS 2015
     
     • “The Implementation and Use of a Generic Dataflow Behaviour in Erlang”

     ACM SIGPLAN Erlang Workshop ’15
     • “Lasp: A Language for Distributed, Eventually Consistent Computations with CRDTs"

     PaPoC 2015
     • “Declarative, Sliding Window Aggregations for Computations at the Edge"

     IEEE EdgeCom 2016
     113
     

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165. SyncFree is a European research project taking place
     for 3 years, staring October 2013, and is funded by
     the European Union, grant agreement n° 609551.
     114
     

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166. Thanks!
     115
     Christopher Meiklejohn
     @cmeik
     

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