Package akka.cluster.sharding

Class ConsistentHashingShardAllocationStrategy

java.lang.Object

akka.cluster.sharding.ConsistentHashingShardAllocationStrategy

All Implemented Interfaces:

NoSerializationVerificationNeeded, ClusterShardAllocationMixin, ShardCoordinator.ActorSystemDependentAllocationStrategy, ShardCoordinator.ShardAllocationStrategy

public class ConsistentHashingShardAllocationStrategy
extends java.lang.Object
implements ShardCoordinator.ActorSystemDependentAllocationStrategy, ClusterShardAllocationMixin

ShardCoordinator.ShardAllocationStrategy that is using consistent hashing. This can be useful when shards with the same shard id for different entity types should be best effort colocated to the same nodes.

When adding or removing nodes it will rebalance according to the new consistent hashing, but that means that only a few shards will be rebalanced and others remain on the same location.

A good explanation of Consistent Hashing: https://tom-e-white.com/2007/11/consistent-hashing.html

Create a new instance of this for each entity types, i.e. a ConsistentHashingShardAllocationStrategy instance must not be shared between different entity types.

Not intended for public inheritance/implementation

Nested Class Summary

Nested classes/interfaces inherited from interface akka.cluster.sharding.internal.ClusterShardAllocationMixin

ClusterShardAllocationMixin.RegionEntry, ClusterShardAllocationMixin.RegionEntry$, ClusterShardAllocationMixin.ShardSuitabilityOrdering$

Constructor Summary

Constructors

Constructor	Description
ConsistentHashingShardAllocationStrategy(int rebalanceLimit)

Method Summary

Modifier and Type	Method	Description
scala.concurrent.Future<ActorRef>	allocateShard(ActorRef requester, java.lang.String shardId, scala.collection.immutable.Map<ActorRef,scala.collection.immutable.IndexedSeq<java.lang.String>> currentShardAllocations)	Invoked when the location of a new shard is to be decided.
protected ClusterEvent.CurrentClusterState	clusterState()
protected LoggingAdapter	log()
scala.concurrent.Future<scala.collection.immutable.Set<java.lang.String>>	rebalance(scala.collection.immutable.Map<ActorRef,scala.collection.immutable.IndexedSeq<java.lang.String>> currentShardAllocations, scala.collection.immutable.Set<java.lang.String> rebalanceInProgress)	Invoked periodically to decide which shards to rebalance to another location.
protected Member	selfMember()
void	start(ActorSystem system)	Called before any calls to allocate/rebalance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface akka.cluster.sharding.internal.ClusterShardAllocationMixin

isAGoodTimeToRebalance, regionEntriesFor

Constructor Detail

ConsistentHashingShardAllocationStrategy

public ConsistentHashingShardAllocationStrategy(int rebalanceLimit)

Method Detail

start

public void start(ActorSystem system)

Description copied from interface: ShardCoordinator.ActorSystemDependentAllocationStrategy

Called before any calls to allocate/rebalance. Do not block. If asynchronous actions are required they can be started here and delay the Futures returned by allocate/rebalance.

Specified by:

start in interface ShardCoordinator.ActorSystemDependentAllocationStrategy

log

protected LoggingAdapter log()

clusterState

protected ClusterEvent.CurrentClusterState clusterState()

Specified by:

clusterState in interface ClusterShardAllocationMixin

selfMember

protected Member selfMember()

Specified by:

selfMember in interface ClusterShardAllocationMixin

allocateShard

public scala.concurrent.Future<ActorRef> allocateShard(ActorRef requester,
                                                       java.lang.String shardId,
                                                       scala.collection.immutable.Map<ActorRef,scala.collection.immutable.IndexedSeq<java.lang.String>> currentShardAllocations)

Description copied from interface: ShardCoordinator.ShardAllocationStrategy

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

Specified by:

allocateShard in interface ShardCoordinator.ShardAllocationStrategy

Parameters:

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

rebalance

public scala.concurrent.Future<scala.collection.immutable.Set<java.lang.String>> rebalance(scala.collection.immutable.Map<ActorRef,scala.collection.immutable.IndexedSeq<java.lang.String>> currentShardAllocations,
                                                                                           scala.collection.immutable.Set<java.lang.String> rebalanceInProgress)

Description copied from interface: ShardCoordinator.ShardAllocationStrategy

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

Specified by:

rebalance in interface ShardCoordinator.ShardAllocationStrategy

Parameters:

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