YATA: collaborative documents and how to make them fast

Slides made for presentation with the same title, made live at Lambda Days conference in July 2022. It discusses technical details behind YATA: a conflict resolution algorithm for rich text CRDT documents used in Yrs/Yrs libraries.

Transcript

1. YATA: COLLABORATIVE DOCS
   AND HOW TO MAKE THEM FAST
   

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2. INTRODUCTION
   Bartosz Sypytkowski
   @Horusiath
   b.sypytkowski@gmail.com
   bartoszsypytkowski.com
   

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3. — When do we need CRDTs
   — YATA: conflict resolution for arrays and maps
   — Update merge & split
   — Optimizations
   AGENDA
   

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4. YJS.DEV
   

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5. PROBLEM STATEMENT
   COLLABORATIVE TEXT EDITOR
   

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6. COLLABORATIVE
   TEXT EDITOR
   Alice
   a
   Carol
   a
   Bob
   a
   

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7. COLLABORATIVE
   TEXT EDITOR
   Alice
   a
   Carol
   a
   Bob
   a
   insert(1, ‘b’) insert(1, ‘c’)
   

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8. COLLABORATIVE
   TEXT EDITOR
   Alice
   a
   Carol
   ac
   Bob
   ab
   

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9. COLLABORATIVE
   TEXT EDITOR
   Alice
   a
   Carol
   ac
   Bob
   ab
   insert(1, ‘b’)
   insert(1, ‘c’)
   insert(1,
   ‘b’) insert(1,
   ‘c’)
   

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10. COLLABORATIVE
    TEXT EDITOR
    Alice
    abc
    Carol
    abc
    Bob
    acb
    

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11. MAYBE JUST SYNCHRONIZE VIA CENTRAL SERVER?
    

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12. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    a
    Carol
    a
    Bob
    a
    server
    a
    

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13. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    a
    Carol
    a
    Bob
    a
    server
    a
    insert(1, ‘b’) insert(1, ‘c’)
    

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14. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    a
    Carol
    a
    Bob
    a
    server
    a
    insert(1, ‘b’) insert(1, ‘c’)
    insert(1,
    ‘b’) insert(1,
    ‘c’)
    E1
    E2
    

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15. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    a
    Carol
    a
    Bob
    a
    server
    ab
    insert(1,
    ‘b’) insert(1,
    ‘b’)
    E2
    insert(1, ‘b’)
    

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16. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    ab
    Carol
    ab
    Bob
    ab
    server
    acb
    insert(1,
    ‘c’) insert(1,
    ‘c’)
    insert(1, ‘c’)
    

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17. SERVER-DRIVEN
    TEXT EDITOR
    Alice
    acb
    Carol
    acb
    Bob
    acb
    server
    acb
    

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18. COMPAR
    ING
    VECTOR
    CLOCKS
    ISSUES
    1. Latency
    2. Online-only / Network issues
    3. Characters interleaving
    4. Server: bottleneck & point of failure
    

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19. FIELDS SHARING
    SIMILAR
    PROBLEMS
    1. Collaborative text editors
    2. Cross-continental data replication
    3. Vehicle apps
    4. Remote areas
    5. One-account/multi-device sync
    

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20. CONFLICT AVOIDANCE
    “Let the majority decide on
    the correct order.”
    Decisions are made by
    quorum
    

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21. CONFLICT AVOIDANCE CONFLICT RESOLUTION
    “Let the majority decide on
    the correct order.”
    “Given enough context
    everyone should come to the
    same conclusion.”
    Decisions are made by
    quorum
    Decisions are made
    individually
    

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22. CONFLICT RESOLUTION
    IT’S ALL ABOUT PRESERVING THE ORIGINAL INTENT
    

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23. SEMANTICS MATTER
    1. Insert characters one after another
    2. Fixing a typo
    3. Move an element
    4. Move a range of elements
    1. Insert characters at positions X, X+1,
    X+2, etc.
    2. Insert/remove character at position X
    3. Remove an element then re-insert it
    4. Delete then re-insert range of
    elements
    

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24. DON’T USE INDEXES FOR POSITIONING
    THEIR MEANING CHANGES OVER TIME
    

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25. LAMPORT CLOCK
    A:1
    Unique peer ID
    Sequence
    Number
    

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26. CONTEXT-AWARE
    INSERTION
    insert_between(A:1, B:1, (B:2, ‘b’))
    

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27. CONTEXT-AWARE
    INSERTION
    insert_between(A:1, B:1, (B:2, ‘b’))
    inserted block ID
    inserted block
    content
    

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28. CONTEXT-AWARE
    INSERTION
    insert_between(A:1, B:1, (B:2, ‘b’))
    left neighbor
    right neighbor
    inserted block ID
    inserted block
    content
    

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29. CONFLICT RESOLUTION
    

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30. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    CONFLICT
    RESOLUTION
    

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31. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    CONFLICT
    RESOLUTION
    

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32. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    CONFLICT
    RESOLUTION
    ?
    

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33. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    CONFLICT
    RESOLUTION
    Use block IDs to skip over blocks
    with lower precedence
    

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34. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    CONFLICT
    RESOLUTION
    

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35. YATA FOR MAPS
    

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36. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    JSON
    Document state
    YMap
    “key” A:1
    ENTRY INSERTION
    YMAP
    

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37. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    JSON
    Document state
    YMap
    “key” A:1
    ENTRY INSERTION
    YMAP
    ymap.set(‘key’, ‘b’)
    

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38. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    JSON
    Document state
    YMap
    “key” A:1
    ENTRY INSERTION
    YMAP
    ymap.set(‘key’, ‘b’)
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    JSON
    Create new block representing insert
    operation
    

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39. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    JSON
    Document state
    YMap
    “key” A:2
    ENTRY INSERTION
    YMAP
    ymap.set(‘key’, ‘b’)
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    JSON
    Insert block at the end of “key”’s
    sequence of values
    

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40. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    length = 1
    DELETED
    Document state
    YMap
    “key” A:2
    ENTRY INSERTION
    YMAP
    ymap.set(‘key’, ‘b’)
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    JSON
    Tombstone all blocks for “key”’s
    values except the latest one
    

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41. MOVING ELEMENTS
    

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42. WHY DON’T JUST USE REMOVE + INSERT?
    

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43. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    

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44. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    

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45. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    

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46. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    Create new block representing move
    operation
    

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47. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    Range 1..2 maps onto continuous
    sequence of blocks from A:2 to B:2
    

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48. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    Destination index 0 suggests to
    insert this block before A:1
    

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49. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    Document state
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    MOVING
    ELEMENTS
    

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50. Document state
    MOVING
    ELEMENTS
    doc.move(1..2, 0)
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    Mark moved elements
    

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51. HOW ARE WE GOING TO READ THAT?
    

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52. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    

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53. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    A:3 A:2..B:2
    Move frame informs if we’re
    currently within moved range
    context
    

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54. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    A:3 A:2..B:2
    Jump to the beginning of moved
    range
    

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55. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    A:3 A:2..B:2
    “b”
    

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56. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    A:3 A:2..B:2
    “b” “c”
    

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57. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    A:3 A:2..B:2
    “b” “c”
    We reached the end of a current
    move frame
    

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58. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    “b” “c”
    

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59. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    “b” “c” “a”
    

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60. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    Move stack
    “b” “c” “a”
    Skip over moved blocks that aren’t
    part of a current move frame
    

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61. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    “b” “c” “a”
    

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62. READING MOVED
    ELEMENTS
    Document state
    A:3
    ID
    NULL
    LEFT
    A:1
    RIGHT
    CONTENT
    (A:2..B:2)
    MOVED
    NULL
    MOVED
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    NULL
    MOVED
    A:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “b”
    STRING
    A:3
    MOVED
    B:2
    ID
    A:1
    LEFT
    B:1
    RIGHT
    CONTENT
    “c”
    STRING
    A:3
    MOVED
    B:1
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “d”
    STRING
    NULL
    MOVED
    ITERATOR
    “b” “c” “a” “d”
    

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63. OPTIMIZATIONS
    1. KNOW YOUR ENVIRONMENT
    

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64. KNOW THE DIFFERENCE
    Peer to Peer Client / Server
    Examples Yjs/Yrs, Automerge RiakDB, AntidoteDB, DynamoDB
    Ops / sec. few* (related to single user activity) > 1000 ops / sec
    Collaborators unknown, limited control known, under full control
    Network / connections heterogenous, unreliable Homogenous, fairly stable
    Data volume fits in memory (hopefully) greater than disk
    

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65. OPTIMIZATIONS
    2. REDUCE NUMBER OF OPERATIONS
    

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66. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    STRING
    Document state
    

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67. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    STRING
    Document state
    Both blocks have sequential IDs
    

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68. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    STRING
    Document state
    Block was intended to be placed
    sequentially
    

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69. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “ab”
    STRING
    Document state
    Block A:1 is responsible for holding 2
    elements now (range from A:1 to A:2)
    

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70. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “ab”
    STRING
    Document state
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “a”
    STRING
    A:2
    ID
    A:1
    LEFT
    NULL
    RIGHT
    CONTENT
    “b”
    STRING
    Document state
    These two representations are logically equivalent
    

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71. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “ab”
    STRING
    A:3
    ID
    A:2
    LEFT
    NULL
    RIGHT
    CONTENT
    “c”
    STRING
    Document state
    Next block ID = last block ID + last
    block length
    insert_between(A:2, NULL, (A:3, ‘c’))
    

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72. OPTIMIZATIONS
    BLOCK MERGING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “ab”
    STRING
    A:3
    ID
    A:2
    LEFT
    NULL
    RIGHT
    CONTENT
    “c”
    STRING
    Document state
    Next block ID = last block ID + last
    block length
    insert_between(A:2, NULL, (A:3, ‘c’))
    Left neighbor point to last ID
    not block ID
    

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73. WHAT IF WE WANT TO INSERT ELEMENT WITHIN BLOCK?
    

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74. A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “helo”
    STRING
    A:5
    ID
    A:3
    LEFT
    A:4
    RIGHT
    CONTENT
    “l”
    STRING
    Document state
    insert_between(A:3, A:4, (A:5, ‘l’))
    OPTIMIZATIONS
    BLOCK SPLITTING
    

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75. A:4
    ID
    A:3
    LEFT
    NULL
    RIGHT
    CONTENT
    “o”
    STRING
    A:5
    ID
    A:3
    LEFT
    A:4
    RIGHT
    CONTENT
    “l”
    STRING
    Document state
    insert_between(A:3, A:4, (A:5, ‘l’))
    OPTIMIZATIONS
    BLOCK SPLITTING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “hel”
    STRING
    Split blocks to create space
    

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76. A:4
    ID
    A:3
    LEFT
    NULL
    RIGHT
    CONTENT
    “o”
    STRING
    A:5
    ID
    A:3
    LEFT
    A:4
    RIGHT
    CONTENT
    “l”
    STRING
    Document state
    OPTIMIZATIONS
    BLOCK SPLITTING
    A:1
    ID
    NULL
    LEFT
    NULL
    RIGHT
    CONTENT
    “hel”
    STRING
    

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77. OPTIMIZATIONS
    3. IMPROVE BLOCK INSERTION TIME
    

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78. PREFER SEQUENTIAL ACCESS WHENEVER POSSIBLE
    

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79. DOCUMENT
    BLOCK
    STRUCTURE
    UNDER THE
    HOOD
    A
    B
    C
    Clients
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Client block list
    Root types
    “name” BRANCH
    START
    Pointer to a CRDT list head
    

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80. DOCUMENT
    BLOCK
    STRUCTURE
    UNDER THE
    HOOD
    A
    B
    C
    Clients
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Client block list
    Root types
    “name” BRANCH
    START
    Pointer to a CRDT list head
    New operation is always
    appended to the end
    

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81. DOCUMENT
    BLOCK
    STRUCTURE
    UNDER THE
    HOOD
    A
    B
    C
    Clients
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Client block list
    Root types
    “name” BRANCH
    START
    Pointer to a CRDT list head
    Finding block by ID (e.g. C:2) is
    done by binary search
    

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82. IT’S ALSO BETTER FOR SYNCHRONIZING DATA
    

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83. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    A
    B
    C
    Block store
    A:1
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Alice Bob
    

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84. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    A
    B
    C
    Block store
    A:1
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Alice Bob
    Bob is missing some of the
    updates from Alice
    

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85. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    A
    B
    C
    Block store
    A:1
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Alice Bob
    Bob creates a vector clock of
    his most recent updates
    A:2
    B:3
    C:4
    

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86. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    A
    B
    C
    Block store
    A:1
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Alice Bob
    Alice compares Bob’s vector
    clock against her own known
    state
    A:2
    B:3
    C:4
    

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87. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    A
    B
    C
    Block store
    A:1
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Alice Bob
    Alice produces a delta with
    blocks that Bob is missing
    A A:2 A:3
    

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88. DELTA REPLICATION
    A
    B
    C
    Block store
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    Root types
    “name” BRANCH
    START
    Block store
    Root types
    “name” BRANCH
    START
    Alice Bob
    Bob applies incoming updates
    on his side
    A A:2 A:3
    A
    B
    C
    A:1 A:2 A:3
    B:1 B:2
    C:1 C:2 C:3
    

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89. OPTIMIZATIONS
    4. INSERTING ELEMENTS CONSECUTIVELY
    

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90. OPTIMIZATIONS
    CACHING LATEST
    POSITION
    let doc = Doc::new();
    let txt = doc.transact().get_text(“text”);
    txt.insert(&mut doc.transact(), 0, “hello”);
    txt.insert(&mut doc.transact(), 5, “world”);
    

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91. MAPPING BETWEEN USER INDEX AND BLOCK ID
    INTRODUCES COST
    

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92. OPTIMIZATIONS
    CURSORS
    let doc = Doc::new();
    let txt = doc.transact().get_text(“text”);
    let mut cursor = txt.seek(0);
    cursor.insert(&mut doc.transact(), “hello”);
    cursor.insert(&mut doc.transact(), “world”);
    

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93. SUMMARY
    

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94. — Yjs/Yrs: https://crates.io/crates/yrs
    — Automerge: https://automerge.org/
    — Ditto.live: https://www.ditto.live/
    — RiakDB: https://riak.com/
    — Amazon DynamoDB: https://aws.amazon.com/dynamodb/
    — AntidoteDB: https://www.antidotedb.eu/
    CRDT PROJECTS
    

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95. — CRDTs deep dive: https://bartoszsypytkowski.com/tag/crdt/
    — List of aggregated CRDT articles: https://crdt.tech
    — Making CRDTs faster: https://josephg.com/blog/crdts-go-brrr/
    REFERENCES
    

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96. THANK YOU
    

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