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RaftMembershipStateMachine.java
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RaftMembershipStateMachine.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.coreedge.raft.membership;
import java.time.Clock;
import java.util.HashSet;
import java.util.Set;
import org.neo4j.coreedge.raft.log.ReadableRaftLog;
import org.neo4j.coreedge.raft.roles.Role;
import org.neo4j.coreedge.raft.state.follower.FollowerStates;
import org.neo4j.coreedge.raft.state.membership.RaftMembershipState;
import org.neo4j.coreedge.server.CoreMember;
import org.neo4j.logging.Log;
import org.neo4j.logging.LogProvider;
import static java.lang.String.format;
/**
* This class carries the core raft membership change state machine, which defines the
* legal state transitions when adding or removing members from the raft voting group.
*
* The state machine has these 4 states:
*
* <pre>
* INACTIVE completely inactive, not leader
*
* IDLE, leader, but idle, no work to do
* CATCHUP IN PROGRESS, member catching up
* CONSENSUS IN PROGRESS caught up member being added to voting group
* </pre>
*
* The normal progression when adding a member is:
* <pre>
* IDLE->CATCHUP->CONSENSUS->IDLE
* </pre>
*
* the normal progression when removing a member is:
* <pre>
* IDLE->CONSENSUS->IDLE
* </pre>
*
* Only a single member change is handled at a time.
*/
class RaftMembershipStateMachine
{
private final Log log;
public RaftMembershipStateMachineEventHandler state = new Inactive();
private final ReadableRaftLog raftLog;
private final Clock clock;
private final long electionTimeout;
private final MembershipDriver membershipDriver;
private long catchupTimeout;
private final RaftMembershipState membershipState;
private CoreMember catchingUpMember;
RaftMembershipStateMachine( ReadableRaftLog raftLog, Clock clock, long electionTimeout,
MembershipDriver membershipDriver, LogProvider logProvider,
long catchupTimeout, RaftMembershipState membershipState )
{
this.raftLog = raftLog;
this.clock = clock;
this.electionTimeout = electionTimeout;
this.membershipDriver = membershipDriver;
this.catchupTimeout = catchupTimeout;
this.membershipState = membershipState;
this.log = logProvider.getLog( getClass() );
}
private synchronized void handleState( RaftMembershipStateMachineEventHandler newState )
{
RaftMembershipStateMachineEventHandler oldState = state;
this.state = newState;
if ( oldState != newState )
{
oldState.onExit();
newState.onEntry();
log.info( newState.toString() );
membershipDriver.stateChanged();
}
}
void onRole( Role role )
{
handleState( state.onRole( role ) );
}
void onRaftGroupCommitted()
{
handleState( state.onRaftGroupCommitted() );
}
void onFollowerStateChange( FollowerStates<CoreMember> followerStates )
{
handleState( state.onFollowerStateChange( followerStates ) );
}
void onMissingMember( CoreMember member )
{
handleState( state.onMissingMember( member ) );
}
void onSuperfluousMember( CoreMember member )
{
handleState( state.onSuperfluousMember( member ) );
}
void onTargetChanged( Set<CoreMember> targetMembers )
{
handleState( state.onTargetChanged( targetMembers ) );
}
private class Inactive extends RaftMembershipStateMachineEventHandler.Adapter
{
@Override
public RaftMembershipStateMachineEventHandler onRole( Role role )
{
if ( role == Role.LEADER )
{
if ( membershipDriver.uncommittedMemberChangeInLog() )
{
return new ConsensusInProgress();
}
else
{
return new Idle();
}
}
return this;
}
@Override
public String toString()
{
return "Inactive{}";
}
}
abstract class ActiveBaseState extends RaftMembershipStateMachineEventHandler.Adapter
{
@Override
public RaftMembershipStateMachineEventHandler onRole( Role role )
{
if ( role != Role.LEADER )
{
return new Inactive();
}
else
{
return this;
}
}
}
private class Idle extends ActiveBaseState
{
@Override
public RaftMembershipStateMachineEventHandler onMissingMember( CoreMember member )
{
return new CatchingUp( member );
}
@Override
public RaftMembershipStateMachineEventHandler onSuperfluousMember( CoreMember member )
{
Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipState.votingMembers() );
updatedVotingMembers.remove( member );
membershipDriver.doConsensus( updatedVotingMembers );
return new ConsensusInProgress();
}
@Override
public String toString()
{
return "Idle{}";
}
}
private class CatchingUp extends ActiveBaseState
{
private final CatchupGoalTracker catchupGoalTracker;
boolean movingToConsensus;
CatchingUp( CoreMember member )
{
this.catchupGoalTracker = new CatchupGoalTracker( raftLog, clock, electionTimeout, catchupTimeout );
catchingUpMember = member;
}
@Override
public void onEntry()
{
membershipState.addAdditionalReplicationMember( catchingUpMember );
log.info( "Adding replication member: " + catchingUpMember );
}
@Override
public void onExit()
{
if( !movingToConsensus )
{
membershipState.removeAdditionalReplicationMember( catchingUpMember );
log.info( "Removing replication member: " + catchingUpMember );
}
}
@Override
public RaftMembershipStateMachineEventHandler onRole( Role role )
{
if ( role != Role.LEADER )
{
return new Inactive();
}
else
{
return this;
}
}
@Override
public RaftMembershipStateMachineEventHandler onFollowerStateChange( FollowerStates<CoreMember> followerStates )
{
catchupGoalTracker.updateProgress( followerStates.get( catchingUpMember ) );
if ( catchupGoalTracker.isFinished() )
{
if ( catchupGoalTracker.isGoalAchieved() )
{
Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipState.votingMembers() );
updatedVotingMembers.add( catchingUpMember );
membershipDriver.doConsensus( updatedVotingMembers );
movingToConsensus = true;
return new ConsensusInProgress();
}
else
{
return new Idle();
}
}
return this;
}
@Override
public RaftMembershipStateMachineEventHandler onTargetChanged( Set targetMembers )
{
if ( !targetMembers.contains( catchingUpMember ) )
{
return new Idle();
}
else
{
return this;
}
}
@Override
public String toString()
{
return format( "CatchingUp{catchupGoalTracker=%s, catchingUpMember=%s}", catchupGoalTracker,
catchingUpMember );
}
}
private class ConsensusInProgress extends ActiveBaseState
{
@Override
public RaftMembershipStateMachineEventHandler onRaftGroupCommitted()
{
return new Idle();
}
@Override
public void onEntry()
{
}
@Override
public void onExit()
{
membershipState.removeAdditionalReplicationMember( catchingUpMember );
log.info( "Removing replication member: " + catchingUpMember );
}
@Override
public String toString()
{
return "ConsensusInProgress{}";
}
}
}