com.hazelcast.quorum

Interface QuorumFunction

All Known Implementing Classes:

ProbabilisticQuorumFunction, RecentlyActiveQuorumFunction

public interface QuorumFunction

A function that can be used to conclude absence/presence of quorum. The quorum function is consulted:

• When a cluster membership change occurs (member added or removed)
• Whenever a hearbeat is received from a member, in case the QuorumFunction also implements HeartbeatAware

A QuorumFunction that implements HeartbeatAware will be also notified of heartbeats. Additionally, a QuorumFunction that implements MembershipListener will be notified of membership events. All listener invocations are executed before the QuorumFunction's apply(Collection) method is invoked. 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.

Method Summary

Modifier and Type	Method and Description
boolean	apply(Collection<Member> members) Determines if quorum is present based on the current list of members in the cluster.

Method Detail

apply

boolean apply(Collection<Member> members)

Determines if quorum is present based on the current list of members in the cluster. Lite members are excluded and only data members are provided to this method.
This method should not block nor execute time-consuming operations, otherwise it may stall other quorum function invocations.

Parameters:

members - snapshot of current member list

Returns:

boolean presence/absence of quorum