FlakeIdGenerator(service_name, name, context)¶
A cluster-wide unique ID generator. Generated IDs are int (long in case of the Python 2 on 32 bit architectures) values and are k-ordered (roughly ordered). IDs are in the range from 0 to 2^63 - 1.
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.
Timestamp component is in milliseconds since 1.1.2018, 0:00 UTC and has 41 bits. This caps the useful lifespan of the generator to little less than 70 years (until ~2088). The sequence component is 6 bits. If more than 64 IDs are requested in single millisecond, IDs will gracefully overflow to the next millisecond and uniqueness is guaranteed in this case. The implementation does not allow overflowing by more than 15 seconds, if IDs are requested at higher rate, the call will block. Note, however, that clients are able to generate even faster because each call goes to a different (random) member and the 64 IDs/ms limit is for single member.
- Node ID overflow:
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.
Generates and returns a cluster-wide unique ID.
This 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.
Values returned from this method may not be strictly ordered.
hazelcast.future.Future[int], new cluster-wide unique ID.
HazelcastError – if node ID for all members in the cluster is out of valid range. See
Node ID overflownote above.