org.axonframework.commandhandling.distributed
Class ConsistentHash

java.lang.Object
  org.axonframework.commandhandling.distributed.ConsistentHash

All Implemented Interfaces:

Externalizable, Serializable

public class ConsistentHash
extends Object
implements Externalizable

Basic implementation of a Consistent Hashing algorithm, using the MD5 algorithm to build the hash values for given keys and node names. It contains some basic operation to add nodes and remove nodes given a set of known remaining members.

Each node contains a Set of supported Commands (as a set of the fully qualified names of payload types). When performing a lookup for a given command, only nodes that support the payload type of the command are eligible.

Since:

2.0

Author:

Allard Buijze

See Also:

Serialized Form

Nested Class Summary

static class

ConsistentHash.Member Represents a member in a consistently hashed cluster.

Constructor Summary

ConsistentHash()
Initializes an empty hash.

Method Summary

static ConsistentHash	emptyRing() Returns an instance of an empty Ring, which can be used to add members.
boolean	equals(Object o)
String	getMember(String item, String commandType) Returns the member for the given item, that supports given commandType.
Set<ConsistentHash.Member>	getMembers() Returns the set of members part of this hash ring.
int	hashCode()
void	readExternal(ObjectInput in)
String	toString()
ConsistentHash	withAdditionalNode(String nodeName, int segmentCount, Set<String> supportedCommandTypes) Returns a ConsistentHash with the given additional nodeName, which is given segmentCount segments on the ring.
ConsistentHash	withExclusively(Collection<String> nodes) Returns a ConsistentHash instance where only segments leading to the given nodes are available.
void	writeExternal(ObjectOutput out)

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ConsistentHash

public ConsistentHash()

Initializes an empty hash.

This constructor is required for serialization. Instead of using this constructor, use emptyRing() to obtain an instance.

Method Detail

emptyRing

public static ConsistentHash emptyRing()

Returns an instance of an empty Ring, which can be used to add members.

Returns:

an empty ConsistentHash ring.

withAdditionalNode

public ConsistentHash withAdditionalNode(String nodeName,
                                         int segmentCount,
                                         Set<String> supportedCommandTypes)

Returns a ConsistentHash with the given additional nodeName, which is given segmentCount segments on the ring. A registration of a node will completely override any previous registration known for that node.

Parameters:

nodeName - The name of the node to add. This will be used to compute the segments

segmentCount - The number of segments to add the given node

supportedCommandTypes - The fully qualified names of command (payload) types this node supports

Returns:

a ConsistentHash with the given additional node

withExclusively

public ConsistentHash withExclusively(Collection<String> nodes)

Returns a ConsistentHash instance where only segments leading to the given nodes are available. Each lookup will always result in one of the given nodes.

Parameters:

nodes - The nodes to keep in the consistent hash

Returns:

a ConsistentHash instance where only segments leading to the given nodes are available

getMember

public String getMember(String item,
                        String commandType)

Returns the member for the given item, that supports given commandType. If no such member is available, this method returns null.

Parameters:

item - The item to find a node name for

commandType - The type of command the member must support

Returns:

The node name for the given item, or null if not found

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

getMembers

public Set<ConsistentHash.Member> getMembers()

Returns the set of members part of this hash ring.

Returns:

the set of members part of this hash ring