Odering in OrbitList

Ordering in OrbitList is done with Interval Tree Clocks (https://github.com/ricardobcl/Interval-Tree-Clocks). Each node tracks a global sequence seq and a local version ver. When an item is added to a list, local version ver is increased by 1. Whenever a list is joined with another list (eg. upon sync), the global sequence seq is set to Max(global.seq, local.seq). When adding an item to the list, the item has a reference to all heads where head is an item that is not referenced by any other item in the list.

Graph

 A   B   C
 
        0.0
         |
0.0     0.1
 |       |
0.1     0.2
   \   /      <--- Sync B with A and C
    1.0   
     |    
    1.1   
   /          <--- Sync A with B
2.0       
   \      
     \        <--- Sync C with A
       \  
        3.0
              <--- Sync ALL

Evolution of the state

Initial state:

A = []
B = []
C = []

Two nodes add events concurrently

Add items to A:

listA.add("mango")
listA.add("banana")

// "A": [
//   { "id": "A", "seq": 0, "ver": 0, "prev": null}
//   { "id": "A", "seq": 0, "ver": 1, "prev": ["A.0.0"]}
// ]

Add items to C:

listC.add("apple")
listC.add("strawberry")
listC.add("orange")

// "C": [
//   { "id": "C", "seq": 0, "ver": 0, "prev": null}
//   { "id": "C", "seq": 0, "ver": 1, "prev": ["C.0.0"]}
//   { "id": "C", "seq": 0, "ver": 2, "prev": ["C.0.1"]}
// ]

B receives a 'sync' from A and C:

B.join(A)
B.join(C)

Add items to B:

listB.add("pineapple")
listB.add("papaya")

// "B": [
//   { "id": "A", "seq": 0, "ver": 0, "prev": null}
//   { "id": "A", "seq": 0, "ver": 1, "prev": ["A.0.0"]}
//   { "id": "C", "seq": 0, "ver": 0, "prev": null}
//   { "id": "C", "seq": 0, "ver": 1, "prev": ["C.0.0"]}
//   { "id": "C", "seq": 0, "ver": 2, "prev": ["C.0.1"]}
//   { "id": "B", "seq": 1, "ver": 0, "prev": ["A.0.1", "C.0.2"]}
//   { "id": "B", "seq": 1, "ver": 1, "prev": ["B.1.0"]}
// ]

A receives a 'sync' from B:

A.join(B)

listA.add("kiwi")

// "A": [
//   { "id": "A", "seq": 0, "ver": 0, "prev": null}
//   { "id": "A", "seq": 0, "ver": 1, "prev": ["A.0.0"]}
//   { "id": "C", "seq": 0, "ver": 0, "prev": null}
//   { "id": "C", "seq": 0, "ver": 1, "prev": ["C.0.0"]}
//   { "id": "C", "seq": 0, "ver": 2, "prev": ["C.0.1"]}
//   { "id": "B", "seq": 1, "ver": 0, "prev": ["A.0.1", "C.0.2"]}
//   { "id": "B", "seq": 1, "ver": 1, "prev": ["B.1.0"]}
//   { "id": "A", "seq": 2, "ver": 0, "prev": ["B.1.1"]}
// ]

C receives a 'sync' from A:

C.join(A)

listC.add("blueberry")

// "C": [
//   { "id": "A", "seq": 0, "ver": 0, "prev": null}
//   { "id": "A", "seq": 0, "ver": 1, "prev": ["A.0.0"]}
//   { "id": "C", "seq": 0, "ver": 0, "prev": null}
//   { "id": "C", "seq": 0, "ver": 1, "prev": ["C.0.0"]}
//   { "id": "C", "seq": 0, "ver": 2, "prev": ["C.0.1"]}
//   { "id": "B", "seq": 1, "ver": 0, "prev": ["A.0.1", "C.0.2"]}
//   { "id": "B", "seq": 1, "ver": 1, "prev": ["B.1.0"]}
//   { "id": "A", "seq": 2, "ver": 0, "prev": ["B.1.1"]}
//   { "id": "C", "seq": 3, "ver": 0, "prev": ["A.2.0"]}
// ]

A receives a 'sync' from C, B receives a 'sync' from C:

A.join(C)
B.join(C)

Converged data set:

{ "id": "A", "seq": 0, "ver": 0, "prev": null},
{ "id": "A", "seq": 0, "ver": 1, "prev": ["A.0.0"]},
{ "id": "C", "seq": 0, "ver": 0, "prev": null},
{ "id": "C", "seq": 0, "ver": 1, "prev": ["C.0.0"]},
{ "id": "C", "seq": 0, "ver": 2, "prev": ["C.0.1"]},
{ "id": "B", "seq": 1, "ver": 0, "prev": ["A.0.1", "C.0.2"]},
{ "id": "B", "seq": 1, "ver": 1, "prev": ["B.1.0"]}
{ "id": "A", "seq": 2, "ver": 0, "prev": ["B.1.1"]}
{ "id": "C", "seq": 3, "ver": 0, "prev": ["A.2.0]"]}

3.6 KiB Raw Blame History

Odering in OrbitList

Graph

Evolution of the state

3.6 KiB

Raw Blame History