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MembershipWaiter.java
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MembershipWaiter.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.util.Set;
import java.util.concurrent.CompletableFuture;
import org.neo4j.coreedge.raft.MismatchedStoreIdService;
import org.neo4j.coreedge.raft.state.ReadableRaftState;
import org.neo4j.coreedge.server.MemberId;
import org.neo4j.kernel.impl.util.JobScheduler;
import org.neo4j.logging.Log;
import org.neo4j.logging.LogProvider;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.neo4j.kernel.impl.util.JobScheduler.SchedulingStrategy.POOLED;
/**
* Waits until member has "fully joined" the raft membership.
* We consider a member fully joined where:
* <ul>
* <li>It is a member of the voting group
* (its opinion will count towards leader elections and committing entries), and</li>
* <li>It is sufficiently caught up with the leader,
* so that long periods of unavailability are unlikely, should the leader fail.</li>
* </ul>
*
* To determine whether the member is sufficiently caught up, we check periodically how far behind we are,
* once every {@code maxCatchupLag}. If the leader is always moving forwards we will never fully catch up,
* so all we look for is that we have caught up with where the leader was the <i>previous</i> time
* that we checked.
*/
public class MembershipWaiter
{
private final MemberId myself;
private final JobScheduler jobScheduler;
private final long maxCatchupLag;
private final MismatchedStoreIdService mismatchedStoreIdService;
private final Log log;
public MembershipWaiter( MemberId myself, JobScheduler jobScheduler, long maxCatchupLag,
MismatchedStoreIdService mismatchedStoreIdService, LogProvider logProvider )
{
this.myself = myself;
this.jobScheduler = jobScheduler;
this.maxCatchupLag = maxCatchupLag;
this.mismatchedStoreIdService = mismatchedStoreIdService;
this.log = logProvider.getLog( getClass() );
}
public CompletableFuture<Boolean> waitUntilCaughtUpMember( ReadableRaftState raftState )
{
CompletableFuture<Boolean> catchUpFuture = new CompletableFuture<>();
Evaluator evaluator = new Evaluator( raftState, catchUpFuture );
mismatchedStoreIdService.addMismatchedStoreListener( evaluator );
JobScheduler.JobHandle jobHandle = jobScheduler.scheduleRecurring(
new JobScheduler.Group( getClass().toString(), POOLED ),
evaluator, maxCatchupLag, MILLISECONDS );
catchUpFuture.whenComplete( ( result, e ) -> jobHandle.cancel( true ) );
return catchUpFuture;
}
private class Evaluator implements Runnable, MismatchedStoreIdService.MismatchedStoreListener
{
private final ReadableRaftState raftState;
private final CompletableFuture<Boolean> catchUpFuture;
private long lastLeaderCommit;
private Evaluator( ReadableRaftState raftState, CompletableFuture<Boolean> catchUpFuture )
{
this.raftState = raftState;
this.catchUpFuture = catchUpFuture;
this.lastLeaderCommit = raftState.leaderCommit();
}
public void run()
{
if ( iAmAVotingMember() && caughtUpWithLeader() )
{
catchUpFuture.complete( true );
}
}
private boolean iAmAVotingMember()
{
Set votingMembers = raftState.votingMembers();
boolean votingMember = votingMembers.contains( myself );
if ( !votingMember )
{
log.debug( "I (%s) am not a voting member: [%s]", myself, votingMembers );
}
return votingMember;
}
private boolean caughtUpWithLeader()
{
boolean caughtUpWithLeader = false;
long localCommit = raftState.commitIndex();
if ( lastLeaderCommit != -1 )
{
caughtUpWithLeader = localCommit >= lastLeaderCommit;
}
lastLeaderCommit = raftState.leaderCommit();
if ( lastLeaderCommit != -1 )
{
long gap = lastLeaderCommit - localCommit;
log.info( "%s Catchup: %d => %d (%d behind)", myself, localCommit, lastLeaderCommit, gap );
}
else
{
log.info( "Leader commit unknown" );
}
return caughtUpWithLeader;
}
@Override
public void onMismatchedStore( MismatchedStoreIdService.MismatchedStoreIdException ex )
{
catchUpFuture.completeExceptionally( ex );
}
}
}