core-edge: better membership storage

The RAFT membership storage is now in line with the intended design
and only stores a single committed state and potentially an additional
appended state. This simplifies the implementation considerably and
improves performance since the dependence on the RAFT log as the
underlying storage is removed. This mismatch was forcing extremely
bad usage patterns of the RAFT log from the membership manager,
causing unnecessary linear scans.

enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/RaftInstance.java

@@ -312,7 +312,6 @@ public synchronized void handle( RaftMessages.RaftMessage incomingMessage )
             handleTimers( outcome );
             handleLogShipping( outcome );
 
-            membershipManager.processLog( outcome.getCommitIndex(), outcome.getLogCommands() );
             driveMembership( outcome );
 
             volatileLeader.set( outcome.getLeader() );
@@ -334,8 +333,10 @@ public synchronized void handle( RaftMessages.RaftMessage incomingMessage )
         }
     }
 
-    private void driveMembership( Outcome outcome )
+    private void driveMembership( Outcome outcome ) throws IOException
     {
+        membershipManager.processLog( outcome.getCommitIndex(), outcome.getLogCommands() );
+
         currentRole = outcome.getRole();
         membershipManager.onRole( currentRole );
 

enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/membership/RaftMembership.java

@@ -40,17 +40,13 @@ public interface RaftMembership
      */
     Set<CoreMember> replicationMembers();
 
-    long logIndex();
-
     /**
      * Register a membership listener.
      *
      * @param listener The listener.
      */
     void registerListener( RaftMembership.Listener listener );
 
-    void deregisterListener( RaftMembership.Listener listener );
-
     /**
      * This interface must be implemented from whoever wants to be notified of membership changes. Membership changes
      * are additions to and removals from the voting and replication members set.

enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/membership/RaftMembershipStateMachine.java → enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/membership/RaftMembershipChanger.java

@@ -26,7 +26,6 @@
 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;
@@ -59,7 +58,7 @@
  *
  * Only a single member change is handled at a time.
  */
-class RaftMembershipStateMachine
+class RaftMembershipChanger
 {
     private final Log log;
     public RaftMembershipStateMachineEventHandler state = new Inactive();
@@ -68,22 +67,19 @@ class RaftMembershipStateMachine
     private final Clock clock;
     private final long electionTimeout;
 
-    private final MembershipDriver membershipDriver;
+    private final RaftMembershipManager membershipManager;
     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 )
+    RaftMembershipChanger( ReadableRaftLog raftLog, Clock clock, long electionTimeout,
+            LogProvider logProvider, long catchupTimeout, RaftMembershipManager membershipManager )
     {
         this.raftLog = raftLog;
         this.clock = clock;
         this.electionTimeout = electionTimeout;
-        this.membershipDriver = membershipDriver;
         this.catchupTimeout = catchupTimeout;
-        this.membershipState = membershipState;
+        this.membershipManager = membershipManager;
         this.log = logProvider.getLog( getClass() );
     }
 
@@ -98,7 +94,7 @@ private synchronized void handleState( RaftMembershipStateMachineEventHandler ne
             newState.onEntry();
 
             log.info( newState.toString() );
-            membershipDriver.stateChanged();
+            membershipManager.stateChanged();
         }
     }
 
@@ -139,7 +135,7 @@ public RaftMembershipStateMachineEventHandler onRole( Role role )
         {
             if ( role == Role.LEADER )
             {
-                if ( membershipDriver.uncommittedMemberChangeInLog() )
+                if ( membershipManager.uncommittedMemberChangeInLog() )
                 {
                     return new ConsensusInProgress();
                 }
@@ -185,9 +181,9 @@ public RaftMembershipStateMachineEventHandler onMissingMember( CoreMember member
         @Override
         public RaftMembershipStateMachineEventHandler onSuperfluousMember( CoreMember member )
         {
-            Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipState.votingMembers() );
+            Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipManager.votingMembers() );
             updatedVotingMembers.remove( member );
-            membershipDriver.doConsensus( updatedVotingMembers );
+            membershipManager.doConsensus( updatedVotingMembers );
 
             return new ConsensusInProgress();
         }
@@ -213,16 +209,16 @@ private class CatchingUp extends ActiveBaseState
         @Override
         public void onEntry()
         {
-            membershipState.addAdditionalReplicationMember( catchingUpMember );
+            membershipManager.addAdditionalReplicationMember( catchingUpMember );
             log.info( "Adding replication member: " + catchingUpMember );
         }
 
         @Override
         public void onExit()
         {
-            if( !movingToConsensus )
+            if ( !movingToConsensus )
             {
-                membershipState.removeAdditionalReplicationMember( catchingUpMember );
+                membershipManager.removeAdditionalReplicationMember( catchingUpMember );
                 log.info( "Removing replication member: " + catchingUpMember );
             }
         }
@@ -249,9 +245,9 @@ public RaftMembershipStateMachineEventHandler onFollowerStateChange( FollowerSta
             {
                 if ( catchupGoalTracker.isGoalAchieved() )
                 {
-                    Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipState.votingMembers() );
+                    Set<CoreMember> updatedVotingMembers = new HashSet<>( membershipManager.votingMembers() );
                     updatedVotingMembers.add( catchingUpMember );
-                    membershipDriver.doConsensus( updatedVotingMembers );
+                    membershipManager.doConsensus( updatedVotingMembers );
 
                     movingToConsensus = true;
                     return new ConsensusInProgress();
@@ -301,7 +297,7 @@ public void onEntry()
         @Override
         public void onExit()
         {
-            membershipState.removeAdditionalReplicationMember( catchingUpMember );
+            membershipManager.removeAdditionalReplicationMember( catchingUpMember );
             log.info( "Removing replication member: " + catchingUpMember );
         }