com.hazelcast.reliableidgen

Interface ReliableIdGenerator

All Superinterfaces:

DistributedObject

All Known Implementing Classes:

ReliableIdGeneratorProxy

public interface ReliableIdGenerator
extends DistributedObject

A cluster-wide unique ID generator. Generated IDs are long primitive values and are k-ordered (roughly ordered). IDs are in the range from Long.MIN_VALUE to Long.MAX_VALUE. This type of generator is generally known as Flake ID generator.

The IDs contain timestamp component and a node ID component, which is assigned when the member joins the cluster. This allows the IDs to be ordered and unique without any coordination between members, which makes the generator safe even in split-brain scenario (for caveats, see here).

Timestamp component is in milliseconds since 1.1.2017, 0:00 UTC, and has 42 bits. This caps the useful lifespan of the generator to little less than 140 years. The sequence component is 6 bits. If more than 64 IDs are requested in single millisecond, IDs will gracefully overflow to next millisecond and uniqueness is guaranteed in this case.

Performance

Operation on member is typically local. On client, the newId() method goes to a random member and gets a batch of IDs, which will then be returned locally for limited time. The pre-fetch size and the validity time can be configured for each client and member, see here for member config and ClientConfig.addReliableIdGeneratorConfig() for client config.

Node ID overflow

Node ID component of the ID has 16 bits. Members with member list join version higher than 2^16 won't be able to generate IDs, but functionality will be preserved by forwarding to another member. It is possible to generate IDs on any member or client as long as there is at least one member with join version smaller than 2^16 in the cluster. The remedy is to restart the cluster: nodeId will be assigned from zero again. Uniqueness after the restart will be preserved thanks to the timestamp component.

Since:

3.10

Method Summary

Modifier and Type	Method and Description
long	newId() Generates and returns a cluster-wide unique ID.

Methods inherited from interface com.hazelcast.core.DistributedObject

destroy, getName, getPartitionKey, getServiceName

Method Detail

newId

long newId()

Generates and returns a cluster-wide unique ID.

The call is typically local on member. A batch of IDs is pre-fetched and then used for preconfigured time locally.

Note: Values returned from this method may be not strictly ordered.

Returns:

new cluster-wide unique ID

Throws:

NodeIdOutOfRangeException - if node ID for all members in the cluster is out of valid range. See "Node ID overflow" in class documentation for more details.

UnsupportedOperationException - if the cluster version is below 3.10