Package org.jgroups.protocols.raft

Class ELECTION

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.raft.election.BaseElection

org.jgroups.protocols.raft.ELECTION

All Implemented Interfaces:

org.jgroups.Lifecycle

public class ELECTION
extends BaseElection

The default leader election algorithm.

Performs leader election. This implementation takes full advantage of JGroup's membership events with View. When the current node is the view coordinator, it starts a voting thread to ask all members to send their information. The voting thread stops when a new leader is elected.

The process that starts the voting thread is not trying to elect itself. The process running the voting process increases its term and asks all nodes about their term and log index information to select the new leader, in the form of VoteResponse. For safety reasons, only the nodes with the most up-to-date log can be elected a leader. With a response from the majority processes, the leader with the higher term and log index is elected. The oldest process (view coordinator) in the system has a priority. Once decided, the process sends a message reliably to everyone identifying the new leader, with the LeaderElected message.

After a leader is elected, a new election round starts on view changes only if the leader left the cluster. In case of losing a majority, the leader steps down.

This implementation is more robust than building with heartbeats, leading to fewer disruptions in the cluster with unnecessary (competing) election rounds. This also means the leader is capable of stepping down. Referred to in §6.2 of Ongaro's dissertation to prevent stale leadership information.

More information is available in the design docs.

Since:

0.1

Author:

Bela Ban

See Also:

• Ongaro's dissertation

Field Summary

Fields

Modifier and Type	Field	Description
protected static final short	ELECTION_ID

Fields inherited from class org.jgroups.protocols.raft.election.BaseElection

num_voting_rounds, PRE_VOTE_REQ, PRE_VOTE_RSP, raft, view, VOTE_REQ, vote_timeout

Fields inherited from class org.jgroups.stack.Protocol

after_creation_hook, down_prot, ergonomics, id, local_addr, log, policies, stack, stats, up_prot

Constructor Summary

Constructors

Constructor	Description
ELECTION()

Method Summary

Modifier and Type	Method	Description
protected void	handleView(org.jgroups.View v)

Methods inherited from class org.jgroups.protocols.raft.election.BaseElection

determineLeader, down, getVotes, handleMessage, init, isMajorityAvailable, isViewCoordinator, isVotingThreadRunning, raft, raft, resetStats, runVotingProcess, runVotingThread, sendLeaderElectedMessage, sendVoteRequest, sendVoteResponse, startVotingThread, stop, stopVotingThread, up, up, up, voteTimeout, voteTimeout

Methods inherited from class org.jgroups.stack.Protocol

accept, addPolicy, addr, addr, afterCreationHook, destroy, down, down, enableStats, getAddress, getComponents, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getLog, getName, getPolicies, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, isErgonomics, level, parse, policies, providedDownServices, providedUpServices, removePolicy, requiredDownServices, requiredUpServices, resetStatistics, setAddress, setDownProtocol, setErgonomics, setId, setLevel, setPolicies, setProtocolStack, setSocketFactory, setUpProtocol, setValue, start, statsEnabled, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Details

ELECTION_ID

protected static final short ELECTION_ID

See Also:

• Constant Field Values

Constructor Details

ELECTION

public ELECTION()

Method Details

handleView

protected void handleView(org.jgroups.View v)

Specified by:

handleView in class BaseElection