com.hazelcast.quorum

Interface QuorumListener

All Superinterfaces:

EventListener

public interface QuorumListener
extends EventListener

Listener to get notified when a quorum state is changed

IMPORTANT: The term "quorum" simply refers to the count of members in the cluster required for an operation to succeed. It does NOT refer to an implementation of Paxos or Raft protocols as used in many NoSQL and distributed systems. The mechanism it provides in Hazelcast protects the user in case the number of nodes in a cluster drops below the specified one.

QuorumEvents are fired only after the quorum is met for the first time. For instance, see the following scenario for a quorum size is equal to 3:

• Member-1 starts; no quorum events are fired, since quorum is not present yet.
• Member-2 starts; no quorum events are fired, since quorum is not present yet.
• Member-3 starts; no quorum events, since this is the first time quorum is met.
• Member-1 stops; both Member-2 and Member-3 fire quorum absent events, since member count drops below 3.
• Member-1 restarts; both Member-2 and Member-3 fire quorum present events, but Member-1 does not, because for Member-1 this is the first time quorum is met.

Method Summary

Modifier and Type	Method and Description
void	onChange(QuorumEvent quorumEvent) Called when quorum presence state is changed.

Method Detail

onChange

void onChange(QuorumEvent quorumEvent)

Called when quorum presence state is changed.

Parameters:

quorumEvent - provides information about quorum presence and current member list.