Package org.jgroups.protocols.raft

Class ELECTION2

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.raft.election.BaseElection

org.jgroups.protocols.raft.ELECTION2

All Implemented Interfaces:

org.jgroups.Lifecycle

public class ELECTION2
extends BaseElection

A leader election protocol.

This implementation extends ELECTION with a pre-vote mechanism. The pre-vote always runs before starting the voting thread to define the leader. The pre-vote increases the delay in electing the leader but, in turn, covers more edge cases. As a rule of thumb, if deploying in an unstable network with frequent partitions, this protocol should give a more stable mechanism, avoid leader disruptions, and avoid possible liveness issues. Otherwise, ELECTION is the default choice.

Pre-Voting phase:

This extension includes the pre-voting mechanism proposed in Ongaro's dissertation (§9.6). In the current implementation, a pre-voting phase starts in case the current node is the new view coordinator and:

• The view coordinator changes and the computed update is Utils.Majority.no_change;
• The computed view update is Utils.Majority.reached or Utils.Majority.leader_lost

The process which executes the pre-voting mechanism sends a PreVoteRequest to all processes in the view. The recipients reply with a PreVoteResponse identifying the node they see as leader. Once the initiator receives the reply from all nodes in the view, it can start the voting process, resuming the work the same as ELECTION.

Since:

1.0.12

Author:

José Bolina

See Also:

• ELECTION
• Ongaro's dissertation
• Issue #221

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
ELECTION2()

Method Summary

Modifier and Type	Method	Description
protected void	handleMessage(org.jgroups.Message msg, RaftHeader hdr)
protected void	handleView(org.jgroups.View v)
boolean	isPreVoteThreadRunning()

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

determineLeader, down, getVotes, 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

ELECTION2

public ELECTION2()

Method Details

isPreVoteThreadRunning

public boolean isPreVoteThreadRunning()

handleView

protected void handleView(org.jgroups.View v)

Specified by:

handleView in class BaseElection

handleMessage

protected void handleMessage(org.jgroups.Message msg,
 RaftHeader hdr)

Overrides:

handleMessage in class BaseElection