Packages

c

akka.cluster.sharding.ShardCoordinator

LeastShardAllocationStrategy

class LeastShardAllocationStrategy extends ShardAllocationStrategy with Serializable

The default implementation of ShardCoordinator.LeastShardAllocationStrategy allocates new shards to the ShardRegion with least number of previously allocated shards.

When a node is removed from the cluster the shards on that node will be started on the remaining nodes, evenly spread on the remaining nodes (by picking regions with least shards).

When a node is added to the cluster the shards on the existing nodes will be rebalanced to the new node. It picks shards for rebalancing from the ShardRegion with most number of previously allocated shards. They will then be allocated to the ShardRegion with least number of previously allocated shards, i.e. new members in the cluster. There is a configurable threshold of how large the difference must be to begin the rebalancing. The difference between number of shards in the region with most shards and the region with least shards must be greater than the rebalanceThreshold for the rebalance to occur.

A rebalanceThreshold of 1 gives the best distribution and therefore typically the best choice. A higher threshold means that more shards can be rebalanced at the same time instead of one-by-one. That has the advantage that the rebalance process can be quicker but has the drawback that the the number of shards (and therefore load) between different nodes may be significantly different. Given the recommendation of using 10x shards than number of nodes and rebalanceThreshold=10 can result in one node hosting ~2 times the number of shards of other nodes. Example: 1000 shards on 100 nodes means 10 shards per node. One node may have 19 shards and others 10 without a rebalance occurring.

The number of ongoing rebalancing processes can be limited by maxSimultaneousRebalance.

Annotations
@SerialVersionUID()
Source
ShardCoordinator.scala
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  1. LeastShardAllocationStrategy
  2. Serializable
  3. Serializable
  4. ShardAllocationStrategy
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Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Instance Constructors

  1. new LeastShardAllocationStrategy(rebalanceThreshold: Int, maxSimultaneousRebalance: Int)

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to any2stringadd[LeastShardAllocationStrategy] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (LeastShardAllocationStrategy, B)
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to ArrowAssoc[LeastShardAllocationStrategy] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  6. def allocateShard(requester: ActorRef, shardId: ShardId, currentShardAllocations: Map[ActorRef, IndexedSeq[ShardId]]): Future[ActorRef]

    Invoked when the location of a new shard is to be decided.

    Invoked when the location of a new shard is to be decided.

    requester

    actor reference to the ShardRegion that requested the location of the shard, can be returned if preference should be given to the node where the shard was first accessed

    shardId

    the id of the shard to allocate

    currentShardAllocations

    all actor refs to ShardRegion and their current allocated shards, in the order they were allocated

    returns

    a Future of the actor ref of the ShardRegion that is to be responsible for the shard, must be one of the references included in the currentShardAllocations parameter

    Definition Classes
    LeastShardAllocationStrategyShardAllocationStrategy
  7. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  8. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native() @HotSpotIntrinsicCandidate()
  9. def ensuring(cond: (LeastShardAllocationStrategy) ⇒ Boolean, msg: ⇒ Any): LeastShardAllocationStrategy
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to Ensuring[LeastShardAllocationStrategy] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  10. def ensuring(cond: (LeastShardAllocationStrategy) ⇒ Boolean): LeastShardAllocationStrategy
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to Ensuring[LeastShardAllocationStrategy] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  11. def ensuring(cond: Boolean, msg: ⇒ Any): LeastShardAllocationStrategy
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to Ensuring[LeastShardAllocationStrategy] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  12. def ensuring(cond: Boolean): LeastShardAllocationStrategy
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to Ensuring[LeastShardAllocationStrategy] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  13. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  14. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  15. def formatted(fmtstr: String): String
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to StringFormat[LeastShardAllocationStrategy] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  16. final def getClass(): Class[_]
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    @native() @HotSpotIntrinsicCandidate()
  17. def hashCode(): Int
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    @native() @HotSpotIntrinsicCandidate()
  18. final def isInstanceOf[T0]: Boolean
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  19. final def ne(arg0: AnyRef): Boolean
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  20. final def notify(): Unit
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    @native() @HotSpotIntrinsicCandidate()
  21. final def notifyAll(): Unit
    Definition Classes
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    @native() @HotSpotIntrinsicCandidate()
  22. def rebalance(currentShardAllocations: Map[ActorRef, IndexedSeq[ShardId]], rebalanceInProgress: Set[ShardId]): Future[Set[ShardId]]

    Invoked periodically to decide which shards to rebalance to another location.

    Invoked periodically to decide which shards to rebalance to another location.

    currentShardAllocations

    all actor refs to ShardRegion and their current allocated shards, in the order they were allocated

    rebalanceInProgress

    set of shards that are currently being rebalanced, i.e. you should not include these in the returned set

    returns

    a Future of the shards to be migrated, may be empty to skip rebalance in this round

    Definition Classes
    LeastShardAllocationStrategyShardAllocationStrategy
  23. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  24. def toString(): String
    Definition Classes
    AnyRef → Any
  25. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
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    @throws( ... )
  26. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
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    @throws( ... ) @native()
  27. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  28. def [B](y: B): (LeastShardAllocationStrategy, B)
    Implicit
    This member is added by an implicit conversion from LeastShardAllocationStrategy to ArrowAssoc[LeastShardAllocationStrategy] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Deprecated Value Members

  1. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
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    Annotations
    @throws( classOf[java.lang.Throwable] ) @Deprecated @deprecated
    Deprecated

    (Since version ) see corresponding Javadoc for more information.

Inherited from Serializable

Inherited from Serializable

Inherited from ShardAllocationStrategy

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from LeastShardAllocationStrategy to any2stringadd[LeastShardAllocationStrategy]

Inherited by implicit conversion StringFormat from LeastShardAllocationStrategy to StringFormat[LeastShardAllocationStrategy]

Inherited by implicit conversion Ensuring from LeastShardAllocationStrategy to Ensuring[LeastShardAllocationStrategy]

Inherited by implicit conversion ArrowAssoc from LeastShardAllocationStrategy to ArrowAssoc[LeastShardAllocationStrategy]

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