Convergent Replicated Data Types

Transcript

1. Convergent Replicated Data Types

2. @vanstee [email protected] Patrick Van Stee

3. “Structuring data so conflict resolution is automatic”

4. Dynamo Trade consistency for availability and partition tolerance

5. Node 1 Node 2 { a: “200” } { a:

   “-3000” } :(

6. Node 1 Node 2 { a: “200” } { a:

   “-3000” } { a: “200”, a: “-3000” } Riak

7. CRDT •Counter •Set •Graph •List •Tree

8. CRDT •Counter •Set •Graph •List •Tree

9. Counter •Can only be increased •Merge: use largest value

10. Chat Room Karma Fault-Tolerant Distributed

11. Serious Business { SB[PVS]: 0} Serious Coding { SB[PVS]: 1}

    # PVS++ { SC[PVS]: 0} { SC[PVS]: 5} # PVS += 5 { SB[PVS]: 2} # PVS++ Merge { SB[PVS]: 2, SC[PVS]: 5} { SB[PVS]: 1, SC[PVS]: 5} { SB[PVS]: 2, SC[PVS]: 5} { PVS: 7}

12. What about decrements? Use separate counters for positive and negative.

    Take the difference for the result.

13. Serious Business { SB[PVS+]: 0, SB[PVS-]: 0 } Serious Coding

    { SB[PVS+]: 1, SB[PVS-]: 0 } # PVS++ { SB[PVS+]: 0, SB[PVS-]: 0 } { SB[PVS+]: 5, SB[PVS-]: 0 } # PVS += 5 { SB[PVS+]: 1, SB[PVS-]: 1 } # PVS-- Merge { PVS+: 6, PVS-: 1 } { PVS+: 6, PVS-: 0 } { PVS+: 6, PVS-: 1 } { PVS: 5 }

14. Set •Can only be added to •Merge: take the union

15. Serious Business { PVS: [ ] } Serious Coding {

    PVS: [] } { PVS: [] } { PVS: [ ] } Merge { PVS: [ , ] } { PVS: [ , ] } { PVS: [ , , ] } { PVS: [ , , ] }

16. Hold on, Can we remove stuff? Use separate sets for

    added and removed elements.

17. Serious Business { PVS+: [ ], PVS-: [] } Serious

    Coding { PVS+: [], PVS-: [] } { PVS+: [], PVS-: [] } { PVS+: [ ], PVS-: [] } Merge { PVS+: [ , ], PVS-: [ ] } { PVS+: [ ], PVS-: [ ] } { PVS+: [ , ], PVS-: [] } { PVS+: [ , ], PVS-: [ ] } { PVS: [ ] }

18. But wait, we can only remove once?

19. U-Set •Append unique values to all set members •Garbage collection

    becomes an issue

20. basho/riak_dt Demo

21. Use Cases •Like button •Page Views •Shopping Cart

22. Reference •INRIA paper •basho/riak_dt •RICON talk

23. Beginning Ruby on Rails Course bignerdranch.com/classes/beginning_ruby_on_rails