Package org.apache.pekko.cluster.ddata

Class LWWMap<A,B>

java.lang.Object
org.apache.pekko.cluster.ddata.LWWMap<A,B>
All Implemented Interfaces:
Serializable, DeltaReplicatedData, RemovedNodePruning, ReplicatedData, ReplicatedDataSerialization
public final class LWWMap<A,B> extends Object implements DeltaReplicatedData, ReplicatedDataSerialization, RemovedNodePruning
Specialized ORMap with LWWRegister values.

LWWRegister relies on synchronized clocks and should only be used when the choice of value is not important for concurrent updates occurring within the clock skew.

Instead of using timestamps based on System.currentTimeMillis() time it is possible to use a timestamp value based on something else, for example an increasing version number from a database record that is used for optimistic concurrency control.

The defaultClock is using max value of System.currentTimeMillis() and currentTimestamp + 1. This means that the timestamp is increased for changes on the same node that occurs within the same millisecond. It also means that it is safe to use the LWWMap without synchronized clocks when there is only one active writer, e.g. a Cluster Singleton. Such a single writer should then first read current value with ReadMajority (or more) before changing and writing the value with WriteMajority (or more).

For first-write-wins semantics you can use the LWWRegister.reverseClock() instead of the LWWRegister.defaultClock()

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

See Also:

  • Method Details

    • empty

      public static <A, B> LWWMap<A,B> empty()

    • apply

      public static LWWMap<Object,Object> apply()

    • create

      public static <A, B> LWWMap<A,B> create()
      Java API

    • unapply

      public static <A, B> scala.Option<scala.collection.immutable.Map<A,B>> unapply(LWWMap<A,B> m)
      Extract the entries().

    • entries

      public scala.collection.immutable.Map<A,B> entries()
      Scala API: All entries of the map.

    • getEntries

      public Map<A,B> getEntries()
      Java API: All entries of the map.

    • get

      public scala.Option<B> get(A key)

    • contains

      public boolean contains(A key)

    • isEmpty

      public boolean isEmpty()

    • size

      public int size()

    • $colon$plus

      public LWWMap<A,B> $colon$plus(scala.Tuple2<A,B> entry, SelfUniqueAddress node)
      Adds an entry to the map

    • put

      public LWWMap<A,B> put(SelfUniqueAddress node, A key, B value)
      Adds an entry to the map

    • put

      public LWWMap<A,B> put(SelfUniqueAddress node, A key, B value, LWWRegister.Clock<B> clock)
      Adds an entry to the map.

      You can provide your clock implementation instead of using timestamps based on System.currentTimeMillis() time. The timestamp can for example be an increasing version number from a database record that is used for optimistic concurrency control.

    • remove

      public LWWMap<A,B> remove(SelfUniqueAddress node, A key)
      Removes an entry from the map. Note that if there is a conflicting update on another node the entry will not be removed after merge.

    • resetDelta

      public LWWMap<A,B> resetDelta()
      Description copied from interface: DeltaReplicatedData
      Reset collection of deltas from mutator operations. When the Replicator invokes the modify function of the Update message the delta is always "reset" and when the user code is invoking one or more mutator operations the data is collecting the delta of the operations and makes it available for the Replicator with the DeltaReplicatedData.delta() accessor. When the Replicator has grabbed the delta it will invoke this method to get a clean data instance without the delta.
      Specified by:
      resetDelta in interface DeltaReplicatedData

    • delta

      public scala.Option<ORMap.DeltaOp> delta()
      Description copied from interface: DeltaReplicatedData
      The accumulated delta of mutator operations since previous DeltaReplicatedData.resetDelta(). When the Replicator invokes the modify function of the Update message and the user code is invoking one or more mutator operations the data is collecting the delta of the operations and makes it available for the Replicator with the DeltaReplicatedData.delta() accessor. The modify function shall still return the full state in the same way as ReplicatedData without support for deltas.
      Specified by:
      delta in interface DeltaReplicatedData

    • mergeDelta

      public LWWMap<A,B> mergeDelta(ORMap.DeltaOp thatDelta)

    • merge

      public LWWMap<A,B> merge(LWWMap<A,B> that)

    • modifiedByNodes

      public scala.collection.immutable.Set<UniqueAddress> modifiedByNodes()
      Description copied from interface: RemovedNodePruning
      The nodes that have changed the state for this data and would need pruning when such node is no longer part of the cluster.
      Specified by:
      modifiedByNodes in interface RemovedNodePruning

    • needPruningFrom

      public boolean needPruningFrom(UniqueAddress removedNode)
      Description copied from interface: RemovedNodePruning
      Does it have any state changes from a specific node, which has been removed from the cluster.
      Specified by:
      needPruningFrom in interface RemovedNodePruning

    • prune

      public LWWMap<A,B> prune(UniqueAddress removedNode, UniqueAddress collapseInto)
      Description copied from interface: RemovedNodePruning
      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.
      Specified by:
      prune in interface RemovedNodePruning

    • pruningCleanup

      public LWWMap<A,B> pruningCleanup(UniqueAddress removedNode)
      Description copied from interface: RemovedNodePruning
      Remove data entries from a node that has been removed from the cluster and already been pruned.
      Specified by:
      pruningCleanup in interface RemovedNodePruning

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object