final class ORSet[A] extends ReplicatedData with ReplicatedDataSerialization with RemovedNodePruning with FastMerge

Implements a 'Observed Remove Set' CRDT, also called a 'OR-Set'. Elements can be added and removed any number of times. Concurrent add wins over remove.

It is not implemented as in the paper A comprehensive study of Convergent and Commutative Replicated Data Types. This is more space efficient and doesn't accumulate garbage for removed elements. It is described in the paper An optimized conflict-free replicated set The implementation is inspired by the Riak DT riak_dt_orswot.

The ORSet has a version vector that is incremented when an element is added to the set. The node -> count pair for that increment is stored against the element as its "birth dot". Every time the element is re-added to the set, its "birth dot" is updated to that of the node -> count version vector entry resulting from the add. When an element is removed, we simply drop it, no tombstones.

When an element exists in replica A and not replica B, is it because A added it and B has not yet seen that, or that B removed it and A has not yet seen that? In this implementation we compare the dot of the present element to the version vector in the Set it is absent from. If the element dot is not "seen" by the Set version vector, that means the other set has yet to see this add, and the item is in the merged Set. If the Set version vector dominates the dot, that means the other Set has removed this element already, and the item is not in the merged Set.

This class is immutable, i.e. "modifying" methods return a new instance.

Annotations
@SerialVersionUID()
Source
ORSet.scala
Linear Supertypes
FastMerge, RemovedNodePruning, ReplicatedDataSerialization, Serializable, Serializable, ReplicatedData, AnyRef, Any
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Inherited
  1. ORSet
  2. FastMerge
  3. RemovedNodePruning
  4. ReplicatedDataSerialization
  5. Serializable
  6. Serializable
  7. ReplicatedData
  8. AnyRef
  9. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
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Type Members

  1. type T = ORSet[A]

    The type of the concrete implementation, e.g.

    The type of the concrete implementation, e.g. GSet[A]. To be specified by subclass.

    Definition Classes
    ORSet → ReplicatedData

Value Members

  1. def +(element: A)(implicit node: Cluster): ORSet[A]

    Adds an element to the set

  2. def -(element: A)(implicit node: Cluster): ORSet[A]

    Removes an element from the set.

  3. def add(node: Cluster, element: A): ORSet[A]

    Adds an element to the set

  4. def clear(node: Cluster): ORSet[A]

    Removes all elements from the set, but keeps the history.

    Removes all elements from the set, but keeps the history. This has the same result as using #remove for each element, but it is more efficient.

  5. def contains(a: A): Boolean
  6. def elements: Set[A]

    Scala API

  7. def equals(o: Any): Boolean
    Definition Classes
    ORSet → AnyRef → Any
  8. def getElements(): Set[A]

    Java API

  9. def hashCode(): Int
    Definition Classes
    ORSet → AnyRef → Any
  10. def isEmpty: Boolean
  11. def merge(that: ORSet[A]): ORSet[A]

    When element is in this Set but not in that Set: Compare the "birth dot" of the present element to the version vector in the Set it is absent from.

    When element is in this Set but not in that Set: Compare the "birth dot" of the present element to the version vector in the Set it is absent from. If the element dot is not "seen" by other Set version vector, that means the other set has yet to see this add, and the element is to be in the merged Set. If the other Set version vector dominates the dot, that means the other Set has removed the element already, and the element is not to be in the merged Set.

    When element in both this Set and in that Set: Some dots may still need to be shed. If this Set has dots that the other Set does not have, and the other Set version vector dominates those dots, then we need to drop those dots. Keep only common dots, and dots that are not dominated by the other sides version vector

    Definition Classes
    ORSet → ReplicatedData
  12. def needPruningFrom(removedNode: UniqueAddress): Boolean

    Does it have any state changes from a specific node, which has been removed from the cluster.

    Does it have any state changes from a specific node, which has been removed from the cluster.

    Definition Classes
    ORSet → RemovedNodePruning
  13. def prune(removedNode: UniqueAddress, collapseInto: UniqueAddress): ORSet[A]

    When the removed node has been removed from the cluster the state changes from that node will be pruned by collapsing the data entries to another node.

    When the removed node has been removed from the cluster the state changes from that node will be pruned by collapsing the data entries to another node.

    Definition Classes
    ORSet → RemovedNodePruning
  14. def pruningCleanup(removedNode: UniqueAddress): ORSet[A]

    Remove data entries from a node that has been removed from the cluster and already been pruned.

    Remove data entries from a node that has been removed from the cluster and already been pruned.

    Definition Classes
    ORSet → RemovedNodePruning
  15. def remove(node: Cluster, element: A): ORSet[A]

    Removes an element from the set.

  16. def size: Int
  17. def toString(): String
    Definition Classes
    ORSet → AnyRef → Any