final class LWWRegister[A] extends ReplicatedData with ReplicatedDataSerialization
Implements a 'Last Writer Wins Register' CRDT, also called a 'LWW-Register'.
It is described in the paper A comprehensive study of Convergent and Commutative Replicated Data Types.
Merge takes the register with highest timestamp. Note that this
relies on synchronized clocks. LWWRegister
should only be used when the choice of
value is not important for concurrent updates occurring within the clock skew.
Merge takes the register updated by the node with lowest address (UniqueAddress
is ordered)
if the timestamps are exactly the same.
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 LWWRegister
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.
- Annotations
- @SerialVersionUID()
- Source
- LWWRegister.scala
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- By Inheritance
- LWWRegister
- ReplicatedDataSerialization
- Serializable
- ReplicatedData
- AnyRef
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- by any2stringadd
- by StringFormat
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- by ArrowAssoc
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- Public
- Protected
Type Members
- type T = LWWRegister[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
- LWWRegister → ReplicatedData
Value Members
- def equals(o: Any): Boolean
- Definition Classes
- LWWRegister → AnyRef → Any
- def getValue(): A
Java API
- def hashCode(): Int
- Definition Classes
- LWWRegister → AnyRef → Any
- def merge(that: LWWRegister[A]): LWWRegister[A]
Monotonic merge function.
Monotonic merge function.
- Definition Classes
- LWWRegister → ReplicatedData
- val timestamp: Long
- def toString(): String
- Definition Classes
- LWWRegister → AnyRef → Any
- def updatedBy: UniqueAddress
The current
value
was set by this node. - val value: A
- def withValue(node: SelfUniqueAddress, value: A): LWWRegister[A]
Change the value of the register.
- def withValue(node: SelfUniqueAddress, value: A, clock: Clock[A]): LWWRegister[A]
Change the value of the register.
Change the value of the register.
You can provide your
clock
implementation instead of using timestamps based onSystem.currentTimeMillis()
time. The timestamp can for example be an increasing version number from a database record that is used for optimistic concurrency control. - def withValueOf(value: A)(implicit node: SelfUniqueAddress, clock: Clock[A] = defaultClock[A]): LWWRegister[A]
Change the value of the register.
Change the value of the register.
You can provide your
clock
implementation instead of using timestamps based onSystem.currentTimeMillis()
time. The timestamp can for example be an increasing version number from a database record that is used for optimistic concurrency control.
Deprecated Value Members
- def withValue(node: Cluster, value: A, clock: Clock[A]): LWWRegister[A]
- Annotations
- @deprecated
- Deprecated
(Since version 2.5.20) Use
withValue
that takes aSelfUniqueAddress
parameter instead.
- def withValue(node: Cluster, value: A): LWWRegister[A]
- Annotations
- @deprecated
- Deprecated
(Since version 2.5.20) Use
withValue
that takes aSelfUniqueAddress
parameter instead.
- def withValue(value: A)(implicit node: Cluster, clock: Clock[A] = defaultClock[A]): LWWRegister[A]
- Annotations
- @deprecated
- Deprecated
(Since version 2.5.20) Use
withValueOf
that takes aSelfUniqueAddress
parameter instead.