Remove ShardMBeanFactory
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / main / java / org / opendaylight / controller / cluster / datastore / Shard.java
index 84c399deb26be96fe969f76bf66692f7ee4b8438..9c548e55f7c2a57bd50ac7c37763798afac6dcc3 100644 (file)
@@ -5,20 +5,28 @@
  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
  * and is available at http://www.eclipse.org/legal/epl-v10.html
  */
-
 package org.opendaylight.controller.cluster.datastore;
 
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.base.Verify.verify;
+import static com.google.common.base.Verify.verifyNotNull;
+import static java.util.Objects.requireNonNull;
+
 import akka.actor.ActorRef;
 import akka.actor.ActorSelection;
 import akka.actor.Cancellable;
+import akka.actor.ExtendedActorSystem;
 import akka.actor.Props;
+import akka.actor.Status;
 import akka.actor.Status.Failure;
+import akka.serialization.JavaSerializer;
 import akka.serialization.Serialization;
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.Optional;
-import com.google.common.base.Preconditions;
 import com.google.common.base.Ticker;
+import com.google.common.base.Verify;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Range;
 import java.io.IOException;
 import java.util.Arrays;
@@ -26,33 +34,38 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalLong;
 import java.util.concurrent.TimeUnit;
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
+import org.eclipse.jdt.annotation.NonNull;
+import org.eclipse.jdt.annotation.Nullable;
 import org.opendaylight.controller.cluster.access.ABIVersion;
 import org.opendaylight.controller.cluster.access.commands.ConnectClientRequest;
 import org.opendaylight.controller.cluster.access.commands.ConnectClientSuccess;
 import org.opendaylight.controller.cluster.access.commands.LocalHistoryRequest;
 import org.opendaylight.controller.cluster.access.commands.NotLeaderException;
+import org.opendaylight.controller.cluster.access.commands.OutOfSequenceEnvelopeException;
 import org.opendaylight.controller.cluster.access.commands.TransactionRequest;
 import org.opendaylight.controller.cluster.access.concepts.ClientIdentifier;
 import org.opendaylight.controller.cluster.access.concepts.FrontendIdentifier;
+import org.opendaylight.controller.cluster.access.concepts.LocalHistoryIdentifier;
 import org.opendaylight.controller.cluster.access.concepts.Request;
 import org.opendaylight.controller.cluster.access.concepts.RequestEnvelope;
 import org.opendaylight.controller.cluster.access.concepts.RequestException;
 import org.opendaylight.controller.cluster.access.concepts.RequestSuccess;
 import org.opendaylight.controller.cluster.access.concepts.RetiredGenerationException;
 import org.opendaylight.controller.cluster.access.concepts.RuntimeRequestException;
+import org.opendaylight.controller.cluster.access.concepts.SliceableMessage;
 import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
 import org.opendaylight.controller.cluster.access.concepts.UnsupportedRequestException;
 import org.opendaylight.controller.cluster.common.actor.CommonConfig;
+import org.opendaylight.controller.cluster.common.actor.Dispatchers;
+import org.opendaylight.controller.cluster.common.actor.Dispatchers.DispatcherType;
 import org.opendaylight.controller.cluster.common.actor.MessageTracker;
 import org.opendaylight.controller.cluster.common.actor.MessageTracker.Error;
 import org.opendaylight.controller.cluster.common.actor.MeteringBehavior;
 import org.opendaylight.controller.cluster.datastore.exceptions.NoShardLeaderException;
 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
-import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardMBeanFactory;
-import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardStats;
 import org.opendaylight.controller.cluster.datastore.messages.AbortTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.ActorInitialized;
 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
@@ -61,34 +74,43 @@ import org.opendaylight.controller.cluster.datastore.messages.CloseTransactionCh
 import org.opendaylight.controller.cluster.datastore.messages.CommitTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.CreateTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.CreateTransactionReply;
-import org.opendaylight.controller.cluster.datastore.messages.DatastoreSnapshot;
-import org.opendaylight.controller.cluster.datastore.messages.DatastoreSnapshot.ShardSnapshot;
 import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
+import org.opendaylight.controller.cluster.datastore.messages.GetKnownClients;
+import org.opendaylight.controller.cluster.datastore.messages.GetKnownClientsReply;
 import org.opendaylight.controller.cluster.datastore.messages.GetShardDataTree;
+import org.opendaylight.controller.cluster.datastore.messages.MakeLeaderLocal;
+import org.opendaylight.controller.cluster.datastore.messages.OnDemandShardState;
 import org.opendaylight.controller.cluster.datastore.messages.PeerAddressResolved;
 import org.opendaylight.controller.cluster.datastore.messages.ReadyLocalTransaction;
-import org.opendaylight.controller.cluster.datastore.messages.RegisterChangeListener;
 import org.opendaylight.controller.cluster.datastore.messages.RegisterDataTreeChangeListener;
 import org.opendaylight.controller.cluster.datastore.messages.ShardLeaderStateChanged;
 import org.opendaylight.controller.cluster.datastore.messages.UpdateSchemaContext;
-import org.opendaylight.controller.cluster.datastore.utils.Dispatchers;
+import org.opendaylight.controller.cluster.datastore.persisted.DatastoreSnapshot;
+import org.opendaylight.controller.cluster.datastore.persisted.DatastoreSnapshot.ShardSnapshot;
+import org.opendaylight.controller.cluster.datastore.persisted.DisableTrackingPayload;
+import org.opendaylight.controller.cluster.messaging.MessageAssembler;
+import org.opendaylight.controller.cluster.messaging.MessageSlicer;
+import org.opendaylight.controller.cluster.messaging.SliceOptions;
 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
 import org.opendaylight.controller.cluster.notifications.RegisterRoleChangeListener;
 import org.opendaylight.controller.cluster.notifications.RoleChangeNotifier;
+import org.opendaylight.controller.cluster.raft.LeadershipTransferFailedException;
 import org.opendaylight.controller.cluster.raft.RaftActor;
 import org.opendaylight.controller.cluster.raft.RaftActorRecoveryCohort;
 import org.opendaylight.controller.cluster.raft.RaftActorSnapshotCohort;
 import org.opendaylight.controller.cluster.raft.RaftState;
 import org.opendaylight.controller.cluster.raft.base.messages.FollowerInitialSyncUpStatus;
+import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
+import org.opendaylight.controller.cluster.raft.messages.RequestLeadership;
 import org.opendaylight.controller.cluster.raft.messages.ServerRemoved;
 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
 import org.opendaylight.yangtools.concepts.Identifier;
+import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataValidationFailedException;
-import org.opendaylight.yangtools.yang.data.api.schema.tree.TipProducingDataTree;
 import org.opendaylight.yangtools.yang.data.api.schema.tree.TreeType;
-import org.opendaylight.yangtools.yang.model.api.SchemaContext;
-import scala.concurrent.duration.Duration;
+import org.opendaylight.yangtools.yang.model.api.EffectiveModelContext;
+import org.opendaylight.yangtools.yang.model.api.EffectiveModelContextProvider;
 import scala.concurrent.duration.FiniteDuration;
 
 /**
@@ -115,11 +137,21 @@ public class Shard extends RaftActor {
         }
     };
 
+    static final Object RESUME_NEXT_PENDING_TRANSACTION = new Object() {
+        @Override
+        public String toString() {
+            return "resumeNextPendingTransaction";
+        }
+    };
+
     // FIXME: shard names should be encapsulated in their own class and this should be exposed as a constant.
     public static final String DEFAULT_NAME = "default";
 
     private static final Collection<ABIVersion> SUPPORTED_ABIVERSIONS;
 
+    // Make sure to keep this in sync with the journal configuration in factory-akka.conf
+    public static final String NON_PERSISTENT_JOURNAL_ID = "akka.persistence.non-persistent.journal";
+
     static {
         final ABIVersion[] values = ABIVersion.values();
         final ABIVersion[] real = Arrays.copyOfRange(values, 1, values.length - 1);
@@ -135,8 +167,12 @@ public class Shard extends RaftActor {
     /// The name of this shard
     private final String name;
 
+    private final String shardName;
+
     private final ShardStats shardMBean;
 
+    private final ShardDataTreeListenerInfoMXBeanImpl listenerInfoMXBean;
+
     private DatastoreContext datastoreContext;
 
     private final ShardCommitCoordinator commitCoordinator;
@@ -154,42 +190,49 @@ public class Shard extends RaftActor {
     private final ShardSnapshotCohort snapshotCohort;
 
     private final DataTreeChangeListenerSupport treeChangeSupport = new DataTreeChangeListenerSupport(this);
-    private final DataChangeListenerSupport changeSupport = new DataChangeListenerSupport(this);
-
 
     private ShardSnapshot restoreFromSnapshot;
 
     private final ShardTransactionMessageRetrySupport messageRetrySupport;
 
-    private final FrontendMetadata frontendMetadata = new FrontendMetadata();
-    private final Map<FrontendIdentifier, LeaderFrontendState> knownFrontends = new HashMap<>();
+    @VisibleForTesting
+    final FrontendMetadata frontendMetadata;
+
+    private Map<FrontendIdentifier, LeaderFrontendState> knownFrontends = ImmutableMap.of();
+    private boolean paused;
+
+    private final MessageSlicer responseMessageSlicer;
+    private final Dispatchers dispatchers;
+
+    private final MessageAssembler requestMessageAssembler;
 
     protected Shard(final AbstractBuilder<?, ?> builder) {
         super(builder.getId().toString(), builder.getPeerAddresses(),
                 Optional.of(builder.getDatastoreContext().getShardRaftConfig()), DataStoreVersions.CURRENT_VERSION);
 
         this.name = builder.getId().toString();
+        this.shardName = builder.getId().getShardName();
         this.datastoreContext = builder.getDatastoreContext();
         this.restoreFromSnapshot = builder.getRestoreFromSnapshot();
+        this.frontendMetadata = new FrontendMetadata(name);
 
         setPersistence(datastoreContext.isPersistent());
 
         LOG.info("Shard created : {}, persistent : {}", name, datastoreContext.isPersistent());
 
         ShardDataTreeChangeListenerPublisherActorProxy treeChangeListenerPublisher =
-                new ShardDataTreeChangeListenerPublisherActorProxy(getContext(), name + "-DTCL-publisher");
-        ShardDataChangeListenerPublisherActorProxy dataChangeListenerPublisher =
-                new ShardDataChangeListenerPublisherActorProxy(getContext(), name + "-DCL-publisher");
+                new ShardDataTreeChangeListenerPublisherActorProxy(getContext(), name + "-DTCL-publisher", name);
         if (builder.getDataTree() != null) {
             store = new ShardDataTree(this, builder.getSchemaContext(), builder.getDataTree(),
-                    treeChangeListenerPublisher, dataChangeListenerPublisher, name);
+                    treeChangeListenerPublisher, name,
+                    frontendMetadata);
         } else {
             store = new ShardDataTree(this, builder.getSchemaContext(), builder.getTreeType(),
-                    builder.getDatastoreContext().getStoreRoot(), treeChangeListenerPublisher,
-                    dataChangeListenerPublisher, name);
+                    builder.getDatastoreContext().getStoreRoot(), treeChangeListenerPublisher, name,
+                    frontendMetadata);
         }
 
-        shardMBean = ShardMBeanFactory.getShardStatsMBean(name, datastoreContext.getDataStoreMXBeanType(), this);
+        shardMBean = ShardStats.create(name, datastoreContext.getDataStoreMXBeanType(), this);
 
         if (isMetricsCaptureEnabled()) {
             getContext().become(new MeteringBehavior(this));
@@ -205,14 +248,29 @@ public class Shard extends RaftActor {
         appendEntriesReplyTracker = new MessageTracker(AppendEntriesReply.class,
                 getRaftActorContext().getConfigParams().getIsolatedCheckIntervalInMillis());
 
+        dispatchers = new Dispatchers(context().system().dispatchers());
         transactionActorFactory = new ShardTransactionActorFactory(store, datastoreContext,
-                new Dispatchers(context().system().dispatchers()).getDispatcherPath(
-                        Dispatchers.DispatcherType.Transaction), self(), getContext(), shardMBean);
+            dispatchers.getDispatcherPath(Dispatchers.DispatcherType.Transaction),
+                self(), getContext(), shardMBean, builder.getId().getShardName());
 
         snapshotCohort = ShardSnapshotCohort.create(getContext(), builder.getId().getMemberName(), store, LOG,
-            this.name);
+            this.name, datastoreContext);
 
         messageRetrySupport = new ShardTransactionMessageRetrySupport(this);
+
+        responseMessageSlicer = MessageSlicer.builder().logContext(this.name)
+                .messageSliceSize(datastoreContext.getMaximumMessageSliceSize())
+                .fileBackedStreamFactory(getRaftActorContext().getFileBackedOutputStreamFactory())
+                .expireStateAfterInactivity(2, TimeUnit.MINUTES).build();
+
+        requestMessageAssembler = MessageAssembler.builder().logContext(this.name)
+                .fileBackedStreamFactory(getRaftActorContext().getFileBackedOutputStreamFactory())
+                .assembledMessageCallback((message, sender) -> self().tell(message, sender))
+                .expireStateAfterInactivity(datastoreContext.getRequestTimeout(), TimeUnit.NANOSECONDS).build();
+
+        listenerInfoMXBean = new ShardDataTreeListenerInfoMXBeanImpl(name, datastoreContext.getDataStoreMXBeanType(),
+                self());
+        listenerInfoMXBean.register();
     }
 
     private void setTransactionCommitTimeout() {
@@ -227,7 +285,7 @@ public class Shard extends RaftActor {
     }
 
     @Override
-    public void postStop() {
+    public void postStop() throws Exception {
         LOG.info("Stopping Shard {}", persistenceId());
 
         super.postStop();
@@ -241,6 +299,7 @@ public class Shard extends RaftActor {
         commitCoordinator.abortPendingTransactions("Transaction aborted due to shutdown.", this);
 
         shardMBean.unregisterMBean();
+        listenerInfoMXBean.unregister();
     }
 
     @Override
@@ -254,33 +313,21 @@ public class Shard extends RaftActor {
         }
     }
 
-    @SuppressWarnings("checkstyle:IllegalCatch")
     @Override
     protected void handleNonRaftCommand(final Object message) {
-        try (final MessageTracker.Context context = appendEntriesReplyTracker.received(message)) {
+        try (MessageTracker.Context context = appendEntriesReplyTracker.received(message)) {
             final Optional<Error> maybeError = context.error();
             if (maybeError.isPresent()) {
                 LOG.trace("{} : AppendEntriesReply failed to arrive at the expected interval {}", persistenceId(),
                     maybeError.get());
             }
 
-            if (message instanceof RequestEnvelope) {
-                final long now = ticker().read();
-                final RequestEnvelope envelope = (RequestEnvelope)message;
+            store.resetTransactionBatch();
 
-                try {
-                    final RequestSuccess<?, ?> success = handleRequest(envelope, now);
-                    if (success != null) {
-                        envelope.sendSuccess(success, ticker().read() - now);
-                    }
-                } catch (RequestException e) {
-                    LOG.debug("{}: request {} failed", persistenceId(), envelope, e);
-                    envelope.sendFailure(e, ticker().read() - now);
-                } catch (Exception e) {
-                    LOG.debug("{}: request {} caused failure", persistenceId(), envelope, e);
-                    envelope.sendFailure(new RuntimeRequestException("Request failed to process", e),
-                        ticker().read() - now);
-                }
+            if (message instanceof RequestEnvelope) {
+                handleRequestEnvelope((RequestEnvelope)message);
+            } else if (MessageAssembler.isHandledMessage(message)) {
+                handleRequestAssemblerMessage(message);
             } else if (message instanceof ConnectClientRequest) {
                 handleConnectClient((ConnectClientRequest)message);
             } else if (CreateTransaction.isSerializedType(message)) {
@@ -299,8 +346,6 @@ public class Shard extends RaftActor {
                 handleAbortTransaction(AbortTransaction.fromSerializable(message));
             } else if (CloseTransactionChain.isSerializedType(message)) {
                 closeTransactionChain(CloseTransactionChain.fromSerializable(message));
-            } else if (message instanceof RegisterChangeListener) {
-                changeSupport.onMessage((RegisterChangeListener) message, isLeader(), hasLeader());
             } else if (message instanceof RegisterDataTreeChangeListener) {
                 treeChangeSupport.onMessage((RegisterDataTreeChangeListener) message, isLeader(), hasLeader());
             } else if (message instanceof UpdateSchemaContext) {
@@ -309,8 +354,7 @@ public class Shard extends RaftActor {
                 PeerAddressResolved resolved = (PeerAddressResolved) message;
                 setPeerAddress(resolved.getPeerId(), resolved.getPeerAddress());
             } else if (TX_COMMIT_TIMEOUT_CHECK_MESSAGE.equals(message)) {
-                store.checkForExpiredTransactions(transactionCommitTimeout);
-                commitCoordinator.checkForExpiredTransactions(transactionCommitTimeout, this);
+                commitTimeoutCheck();
             } else if (message instanceof DatastoreContext) {
                 onDatastoreContext((DatastoreContext)message);
             } else if (message instanceof RegisterRoleChangeListener) {
@@ -329,23 +373,143 @@ public class Shard extends RaftActor {
             } else if (message instanceof DataTreeCohortActorRegistry.CohortRegistryCommand) {
                 store.processCohortRegistryCommand(getSender(),
                         (DataTreeCohortActorRegistry.CohortRegistryCommand) message);
-            } else {
+            } else if (message instanceof MakeLeaderLocal) {
+                onMakeLeaderLocal();
+            } else if (RESUME_NEXT_PENDING_TRANSACTION.equals(message)) {
+                store.resumeNextPendingTransaction();
+            } else if (GetKnownClients.INSTANCE.equals(message)) {
+                handleGetKnownClients();
+            } else if (!responseMessageSlicer.handleMessage(message)) {
                 super.handleNonRaftCommand(message);
             }
         }
     }
 
+    private void handleRequestAssemblerMessage(final Object message) {
+        dispatchers.getDispatcher(DispatcherType.Serialization).execute(() -> {
+            JavaSerializer.currentSystem().value_$eq((ExtendedActorSystem) context().system());
+            requestMessageAssembler.handleMessage(message, self());
+        });
+    }
+
+    @SuppressWarnings("checkstyle:IllegalCatch")
+    private void handleRequestEnvelope(final RequestEnvelope envelope) {
+        final long now = ticker().read();
+        try {
+            final RequestSuccess<?, ?> success = handleRequest(envelope, now);
+            if (success != null) {
+                final long executionTimeNanos = ticker().read() - now;
+                if (success instanceof SliceableMessage) {
+                    dispatchers.getDispatcher(DispatcherType.Serialization).execute(() ->
+                        responseMessageSlicer.slice(SliceOptions.builder().identifier(success.getTarget())
+                            .message(envelope.newSuccessEnvelope(success, executionTimeNanos))
+                            .sendTo(envelope.getMessage().getReplyTo()).replyTo(self())
+                            .onFailureCallback(t -> LOG.warn("Error slicing response {}", success, t)).build()));
+                } else {
+                    envelope.sendSuccess(success, executionTimeNanos);
+                }
+            }
+        } catch (RequestException e) {
+            LOG.debug("{}: request {} failed", persistenceId(), envelope, e);
+            envelope.sendFailure(e, ticker().read() - now);
+        } catch (Exception e) {
+            LOG.debug("{}: request {} caused failure", persistenceId(), envelope, e);
+            envelope.sendFailure(new RuntimeRequestException("Request failed to process", e),
+                ticker().read() - now);
+        }
+    }
+
+    private void commitTimeoutCheck() {
+        store.checkForExpiredTransactions(transactionCommitTimeout, this::updateAccess);
+        commitCoordinator.checkForExpiredTransactions(transactionCommitTimeout, this);
+        requestMessageAssembler.checkExpiredAssembledMessageState();
+    }
+
+    private OptionalLong updateAccess(final SimpleShardDataTreeCohort cohort) {
+        final FrontendIdentifier frontend = cohort.getIdentifier().getHistoryId().getClientId().getFrontendId();
+        final LeaderFrontendState state = knownFrontends.get(frontend);
+        if (state == null) {
+            // Not tell-based protocol, do nothing
+            return OptionalLong.empty();
+        }
+
+        if (isIsolatedLeader()) {
+            // We are isolated and no new request can come through until we emerge from it. We are still updating
+            // liveness of frontend when we see it attempting to communicate. Use the last access timer.
+            return OptionalLong.of(state.getLastSeenTicks());
+        }
+
+        // If this frontend has freshly connected, give it some time to catch up before killing its transactions.
+        return OptionalLong.of(state.getLastConnectTicks());
+    }
+
+    private void disableTracking(final DisableTrackingPayload payload) {
+        final ClientIdentifier clientId = payload.getIdentifier();
+        LOG.debug("{}: disabling tracking of {}", persistenceId(), clientId);
+        frontendMetadata.disableTracking(clientId);
+
+        if (isLeader()) {
+            final FrontendIdentifier frontendId = clientId.getFrontendId();
+            final LeaderFrontendState frontend = knownFrontends.get(frontendId);
+            if (frontend != null) {
+                if (clientId.equals(frontend.getIdentifier())) {
+                    if (!(frontend instanceof LeaderFrontendState.Disabled)) {
+                        verify(knownFrontends.replace(frontendId, frontend,
+                            new LeaderFrontendState.Disabled(persistenceId(), clientId, store)));
+                        LOG.debug("{}: leader state for {} disabled", persistenceId(), clientId);
+                    } else {
+                        LOG.debug("{}: leader state {} is already disabled", persistenceId(), frontend);
+                    }
+                } else {
+                    LOG.debug("{}: leader state {} does not match {}", persistenceId(), frontend, clientId);
+                }
+            } else {
+                LOG.debug("{}: leader state for {} not found", persistenceId(), clientId);
+                knownFrontends.put(frontendId, new LeaderFrontendState.Disabled(persistenceId(), clientId,
+                    getDataStore()));
+            }
+        }
+    }
+
+    private void onMakeLeaderLocal() {
+        LOG.debug("{}: onMakeLeaderLocal received", persistenceId());
+        if (isLeader()) {
+            getSender().tell(new Status.Success(null), getSelf());
+            return;
+        }
+
+        final ActorSelection leader = getLeader();
+
+        if (leader == null) {
+            // Leader is not present. The cluster is most likely trying to
+            // elect a leader and we should let that run its normal course
+
+            // TODO we can wait for the election to complete and retry the
+            // request. We can also let the caller retry by sending a flag
+            // in the response indicating the request is "reTryable".
+            getSender().tell(new Failure(
+                    new LeadershipTransferFailedException("We cannot initiate leadership transfer to local node. "
+                            + "Currently there is no leader for " + persistenceId())),
+                    getSelf());
+            return;
+        }
+
+        leader.tell(new RequestLeadership(getId(), getSender()), getSelf());
+    }
+
     // Acquire our frontend tracking handle and verify generation matches
-    private LeaderFrontendState getFrontend(final ClientIdentifier clientId) throws RequestException {
+    private @Nullable LeaderFrontendState findFrontend(final ClientIdentifier clientId) throws RequestException {
         final LeaderFrontendState existing = knownFrontends.get(clientId.getFrontendId());
         if (existing != null) {
             final int cmp = Long.compareUnsigned(existing.getIdentifier().getGeneration(), clientId.getGeneration());
             if (cmp == 0) {
+                existing.touch();
                 return existing;
             }
             if (cmp > 0) {
                 LOG.debug("{}: rejecting request from outdated client {}", persistenceId(), clientId);
-                throw new RetiredGenerationException(existing.getIdentifier().getGeneration());
+                throw new RetiredGenerationException(clientId.getGeneration(),
+                    existing.getIdentifier().getGeneration());
             }
 
             LOG.info("{}: retiring state {}, outdated by request from client {}", persistenceId(), existing, clientId);
@@ -355,13 +519,20 @@ public class Shard extends RaftActor {
             LOG.debug("{}: client {} is not yet known", persistenceId(), clientId);
         }
 
-        final LeaderFrontendState ret = new LeaderFrontendState(persistenceId(), clientId, store);
-        knownFrontends.put(clientId.getFrontendId(), ret);
-        LOG.debug("{}: created state {} for client {}", persistenceId(), ret, clientId);
-        return ret;
+        return null;
     }
 
-    private static @Nonnull ABIVersion selectVersion(final ConnectClientRequest message) {
+    private LeaderFrontendState getFrontend(final ClientIdentifier clientId) throws RequestException {
+        final LeaderFrontendState ret = findFrontend(clientId);
+        if (ret != null) {
+            return ret;
+        }
+
+        // TODO: a dedicated exception would be better, but this is technically true, too
+        throw new OutOfSequenceEnvelopeException(0);
+    }
+
+    private static @NonNull ABIVersion selectVersion(final ConnectClientRequest message) {
         final Range<ABIVersion> clientRange = Range.closed(message.getMinVersion(), message.getMaxVersion());
         for (ABIVersion v : SUPPORTED_ABIVERSIONS) {
             if (clientRange.contains(v)) {
@@ -377,13 +548,29 @@ public class Shard extends RaftActor {
     @SuppressWarnings("checkstyle:IllegalCatch")
     private void handleConnectClient(final ConnectClientRequest message) {
         try {
+            final ClientIdentifier clientId = message.getTarget();
+            final LeaderFrontendState existing = findFrontend(clientId);
+            if (existing != null) {
+                existing.touch();
+            }
+
             if (!isLeader() || !isLeaderActive()) {
-                LOG.debug("{}: not currently leader, rejecting request {}", persistenceId(), message);
+                LOG.info("{}: not currently leader, rejecting request {}. isLeader: {}, isLeaderActive: {},"
+                                + "isLeadershipTransferInProgress: {}.",
+                        persistenceId(), message, isLeader(), isLeaderActive(), isLeadershipTransferInProgress());
                 throw new NotLeaderException(getSelf());
             }
 
             final ABIVersion selectedVersion = selectVersion(message);
-            final LeaderFrontendState frontend = getFrontend(message.getTarget());
+            final LeaderFrontendState frontend;
+            if (existing == null) {
+                frontend = new LeaderFrontendState.Enabled(persistenceId(), clientId, store);
+                knownFrontends.put(clientId.getFrontendId(), frontend);
+                LOG.debug("{}: created state {} for client {}", persistenceId(), frontend, clientId);
+            } else {
+                frontend = existing;
+            }
+
             frontend.reconnect();
             message.getReplyTo().tell(new ConnectClientSuccess(message.getTarget(), message.getSequence(), getSelf(),
                 ImmutableList.of(), store.getDataTree(), CLIENT_MAX_MESSAGES).toVersion(selectedVersion),
@@ -396,8 +583,10 @@ public class Shard extends RaftActor {
     private @Nullable RequestSuccess<?, ?> handleRequest(final RequestEnvelope envelope, final long now)
             throws RequestException {
         // We are not the leader, hence we want to fail-fast.
-        if (!isLeader() || !isLeaderActive()) {
-            LOG.debug("{}: not currently leader, rejecting request {}", persistenceId(), envelope);
+        if (!isLeader() || paused || !isLeaderActive()) {
+            LOG.debug("{}: not currently active leader, rejecting request {}. isLeader: {}, isLeaderActive: {},"
+                            + "isLeadershipTransferInProgress: {}, paused: {}",
+                    persistenceId(), envelope, isLeader(), isLeaderActive(), isLeadershipTransferInProgress(), paused);
             throw new NotLeaderException(getSelf());
         }
 
@@ -411,11 +600,23 @@ public class Shard extends RaftActor {
             final ClientIdentifier clientId = lhReq.getTarget().getClientId();
             return getFrontend(clientId).handleLocalHistoryRequest(lhReq, envelope, now);
         } else {
-            LOG.debug("{}: rejecting unsupported request {}", persistenceId(), request);
+            LOG.warn("{}: rejecting unsupported request {}", persistenceId(), request);
             throw new UnsupportedRequestException(request);
         }
     }
 
+    private void handleGetKnownClients() {
+        final ImmutableSet<ClientIdentifier> clients;
+        if (isLeader()) {
+            clients = knownFrontends.values().stream()
+                    .map(LeaderFrontendState::getIdentifier)
+                    .collect(ImmutableSet.toImmutableSet());
+        } else {
+            clients = frontendMetadata.getClients();
+        }
+        sender().tell(new GetKnownClientsReply(clients), self());
+    }
+
     private boolean hasLeader() {
         return getLeaderId() != null;
     }
@@ -433,6 +634,10 @@ public class Shard extends RaftActor {
         return roleChangeNotifier;
     }
 
+    String getShardName() {
+        return shardName;
+    }
+
     @Override
     protected LeaderStateChanged newLeaderStateChanged(final String memberId, final String leaderId,
             final short leaderPayloadVersion) {
@@ -441,7 +646,7 @@ public class Shard extends RaftActor {
     }
 
     protected void onDatastoreContext(final DatastoreContext context) {
-        datastoreContext = context;
+        datastoreContext = verifyNotNull(context);
 
         setTransactionCommitTimeout();
 
@@ -451,24 +656,25 @@ public class Shard extends RaftActor {
     }
 
     // applyState() will be invoked once consensus is reached on the payload
-    void persistPayload(final TransactionIdentifier transactionId, final Payload payload, boolean batchHint) {
+    void persistPayload(final Identifier id, final Payload payload, final boolean batchHint) {
         boolean canSkipPayload = !hasFollowers() && !persistence().isRecoveryApplicable();
         if (canSkipPayload) {
-            applyState(self(), transactionId, payload);
+            applyState(self(), id, payload);
         } else {
             // We are faking the sender
-            persistData(self(), transactionId, payload, batchHint);
+            persistData(self(), id, payload, batchHint);
         }
     }
 
     private void handleCommitTransaction(final CommitTransaction commit) {
+        final TransactionIdentifier txId = commit.getTransactionId();
         if (isLeader()) {
-            commitCoordinator.handleCommit(commit.getTransactionId(), getSender(), this);
+            askProtocolEncountered(txId);
+            commitCoordinator.handleCommit(txId, getSender(), this);
         } else {
             ActorSelection leader = getLeader();
             if (leader == null) {
-                messageRetrySupport.addMessageToRetry(commit, getSender(),
-                        "Could not commit transaction " + commit.getTransactionId());
+                messageRetrySupport.addMessageToRetry(commit, getSender(), "Could not commit transaction " + txId);
             } else {
                 LOG.debug("{}: Forwarding CommitTransaction to leader {}", persistenceId(), leader);
                 leader.forward(commit, getContext());
@@ -477,15 +683,17 @@ public class Shard extends RaftActor {
     }
 
     private void handleCanCommitTransaction(final CanCommitTransaction canCommit) {
-        LOG.debug("{}: Can committing transaction {}", persistenceId(), canCommit.getTransactionId());
+        final TransactionIdentifier txId = canCommit.getTransactionId();
+        LOG.debug("{}: Can committing transaction {}", persistenceId(), txId);
 
         if (isLeader()) {
-            commitCoordinator.handleCanCommit(canCommit.getTransactionId(), getSender(), this);
+            askProtocolEncountered(txId);
+            commitCoordinator.handleCanCommit(txId, getSender(), this);
         } else {
             ActorSelection leader = getLeader();
             if (leader == null) {
                 messageRetrySupport.addMessageToRetry(canCommit, getSender(),
-                        "Could not canCommit transaction " + canCommit.getTransactionId());
+                        "Could not canCommit transaction " + txId);
             } else {
                 LOG.debug("{}: Forwarding CanCommitTransaction to leader {}", persistenceId(), leader);
                 leader.forward(canCommit, getContext());
@@ -495,6 +703,8 @@ public class Shard extends RaftActor {
 
     @SuppressWarnings("checkstyle:IllegalCatch")
     protected void handleBatchedModificationsLocal(final BatchedModifications batched, final ActorRef sender) {
+        askProtocolEncountered(batched.getTransactionId());
+
         try {
             commitCoordinator.handleBatchedModifications(batched, sender, this);
         } catch (Exception e) {
@@ -524,7 +734,7 @@ public class Shard extends RaftActor {
             ActorSelection leader = getLeader();
             if (!isLeaderActive || leader == null) {
                 messageRetrySupport.addMessageToRetry(batched, getSender(),
-                        "Could not commit transaction " + batched.getTransactionId());
+                        "Could not process BatchedModifications " + batched.getTransactionId());
             } else {
                 // If this is not the first batch and leadership changed in between batched messages,
                 // we need to reconstruct previous BatchedModifications from the transaction
@@ -577,7 +787,7 @@ public class Shard extends RaftActor {
             ActorSelection leader = getLeader();
             if (!isLeaderActive || leader == null) {
                 messageRetrySupport.addMessageToRetry(message, getSender(),
-                        "Could not commit transaction " + message.getTransactionId());
+                        "Could not process ready local transaction " + message.getTransactionId());
             } else {
                 LOG.debug("{}: Forwarding ReadyLocalTransaction to leader {}", persistenceId(), leader);
                 message.setRemoteVersion(getCurrentBehavior().getLeaderPayloadVersion());
@@ -591,17 +801,19 @@ public class Shard extends RaftActor {
 
         boolean isLeaderActive = isLeaderActive();
         if (isLeader() && isLeaderActive) {
+            askProtocolEncountered(forwardedReady.getTransactionId());
             commitCoordinator.handleForwardedReadyTransaction(forwardedReady, getSender(), this);
         } else {
             ActorSelection leader = getLeader();
             if (!isLeaderActive || leader == null) {
                 messageRetrySupport.addMessageToRetry(forwardedReady, getSender(),
-                        "Could not commit transaction " + forwardedReady.getTransactionId());
+                        "Could not process forwarded ready transaction " + forwardedReady.getTransactionId());
             } else {
                 LOG.debug("{}: Forwarding ForwardedReadyTransaction to leader {}", persistenceId(), leader);
 
                 ReadyLocalTransaction readyLocal = new ReadyLocalTransaction(forwardedReady.getTransactionId(),
-                        forwardedReady.getTransaction().getSnapshot(), forwardedReady.isDoImmediateCommit());
+                        forwardedReady.getTransaction().getSnapshot(), forwardedReady.isDoImmediateCommit(),
+                        forwardedReady.getParticipatingShardNames());
                 readyLocal.setRemoteVersion(getCurrentBehavior().getLeaderPayloadVersion());
                 leader.forward(readyLocal, getContext());
             }
@@ -609,10 +821,12 @@ public class Shard extends RaftActor {
     }
 
     private void handleAbortTransaction(final AbortTransaction abort) {
-        doAbortTransaction(abort.getTransactionId(), getSender());
+        final TransactionIdentifier transactionId = abort.getTransactionId();
+        askProtocolEncountered(transactionId);
+        doAbortTransaction(transactionId, getSender());
     }
 
-    void doAbortTransaction(final TransactionIdentifier transactionID, final ActorRef sender) {
+    void doAbortTransaction(final Identifier transactionID, final ActorRef sender) {
         commitCoordinator.handleAbort(transactionID, sender, this);
     }
 
@@ -628,11 +842,21 @@ public class Shard extends RaftActor {
     }
 
     private void closeTransactionChain(final CloseTransactionChain closeTransactionChain) {
-        store.closeTransactionChain(closeTransactionChain.getIdentifier());
+        if (isLeader()) {
+            final LocalHistoryIdentifier id = closeTransactionChain.getIdentifier();
+            askProtocolEncountered(id.getClientId());
+            store.closeTransactionChain(id);
+        } else if (getLeader() != null) {
+            getLeader().forward(closeTransactionChain, getContext());
+        } else {
+            LOG.warn("{}: Could not close transaction {}", persistenceId(), closeTransactionChain.getIdentifier());
+        }
     }
 
     @SuppressWarnings("checkstyle:IllegalCatch")
     private void createTransaction(final CreateTransaction createTransaction) {
+        askProtocolEncountered(createTransaction.getTransactionId());
+
         try {
             if (TransactionType.fromInt(createTransaction.getTransactionType()) != TransactionType.READ_ONLY
                     && failIfIsolatedLeader(getSender())) {
@@ -655,12 +879,33 @@ public class Shard extends RaftActor {
             transactionId);
     }
 
+    // Called on leader only
+    private void askProtocolEncountered(final TransactionIdentifier transactionId) {
+        askProtocolEncountered(transactionId.getHistoryId().getClientId());
+    }
+
+    // Called on leader only
+    private void askProtocolEncountered(final ClientIdentifier clientId) {
+        final FrontendIdentifier frontend = clientId.getFrontendId();
+        final LeaderFrontendState state = knownFrontends.get(frontend);
+        if (!(state instanceof LeaderFrontendState.Disabled)) {
+            LOG.debug("{}: encountered ask-based client {}, disabling transaction tracking", persistenceId(), clientId);
+            if (knownFrontends.isEmpty()) {
+                knownFrontends = new HashMap<>();
+            }
+            knownFrontends.put(frontend, new LeaderFrontendState.Disabled(persistenceId(), clientId, getDataStore()));
+
+            persistPayload(clientId, DisableTrackingPayload.create(clientId,
+                datastoreContext.getInitialPayloadSerializedBufferCapacity()), false);
+        }
+    }
+
     private void updateSchemaContext(final UpdateSchemaContext message) {
-        updateSchemaContext(message.getSchemaContext());
+        updateSchemaContext(message.getEffectiveModelContext());
     }
 
     @VisibleForTesting
-    void updateSchemaContext(final SchemaContext schemaContext) {
+    void updateSchemaContext(final @NonNull EffectiveModelContext schemaContext) {
         store.updateSchemaContext(schemaContext);
     }
 
@@ -676,10 +921,12 @@ public class Shard extends RaftActor {
     }
 
     @Override
-    @Nonnull
     protected RaftActorRecoveryCohort getRaftActorRecoveryCohort() {
-        return new ShardRecoveryCoordinator(store,
-            restoreFromSnapshot != null ? restoreFromSnapshot.getSnapshot() : null, persistenceId(), LOG);
+        if (restoreFromSnapshot == null) {
+            return ShardRecoveryCoordinator.create(store, persistenceId(), LOG);
+        }
+
+        return ShardRecoveryCoordinator.forSnapshot(store, persistenceId(), LOG, restoreFromSnapshot.getSnapshot());
     }
 
     @Override
@@ -693,7 +940,7 @@ public class Shard extends RaftActor {
         if (txCommitTimeoutCheckSchedule == null) {
             // Schedule a message to be periodically sent to check if the current in-progress
             // transaction should be expired and aborted.
-            FiniteDuration period = Duration.create(transactionCommitTimeout / 3, TimeUnit.MILLISECONDS);
+            FiniteDuration period = FiniteDuration.create(transactionCommitTimeout / 3, TimeUnit.MILLISECONDS);
             txCommitTimeoutCheckSchedule = getContext().system().scheduler().schedule(
                     period, period, getSelf(),
                     TX_COMMIT_TIMEOUT_CHECK_MESSAGE, getContext().dispatcher(), ActorRef.noSender());
@@ -703,6 +950,11 @@ public class Shard extends RaftActor {
     @Override
     protected void applyState(final ActorRef clientActor, final Identifier identifier, final Object data) {
         if (data instanceof Payload) {
+            if (data instanceof DisableTrackingPayload) {
+                disableTracking((DisableTrackingPayload) data);
+                return;
+            }
+
             try {
                 store.applyReplicatedPayload(identifier, (Payload)data);
             } catch (DataValidationFailedException | IOException e) {
@@ -717,7 +969,6 @@ public class Shard extends RaftActor {
     protected void onStateChanged() {
         boolean isLeader = isLeader();
         boolean hasLeader = hasLeader();
-        changeSupport.onLeadershipChange(isLeader, hasLeader);
         treeChangeSupport.onLeadershipChange(isLeader, hasLeader);
 
         // If this actor is no longer the leader close all the transaction chains
@@ -728,7 +979,8 @@ public class Shard extends RaftActor {
                     persistenceId(), getId());
             }
 
-            store.closeAllTransactionChains();
+            paused = false;
+            store.purgeLeaderState();
         }
 
         if (hasLeader && !isIsolatedLeader()) {
@@ -739,9 +991,21 @@ public class Shard extends RaftActor {
     @Override
     protected void onLeaderChanged(final String oldLeader, final String newLeader) {
         shardMBean.incrementLeadershipChangeCount();
+        paused = false;
+
+        if (!isLeader()) {
+            if (!knownFrontends.isEmpty()) {
+                LOG.debug("{}: removing frontend state for {}", persistenceId(), knownFrontends.keySet());
+                knownFrontends = ImmutableMap.of();
+            }
+
+            requestMessageAssembler.close();
+
+            if (!hasLeader()) {
+                // No leader anywhere, nothing else to do
+                return;
+            }
 
-        boolean hasLeader = hasLeader();
-        if (hasLeader && !isLeader()) {
             // Another leader was elected. If we were the previous leader and had pending transactions, convert
             // them to transaction messages and send to the new leader.
             ActorSelection leader = getLeader();
@@ -753,6 +1017,8 @@ public class Shard extends RaftActor {
                             messagesToForward.size(), leader);
 
                     for (Object message : messagesToForward) {
+                        LOG.debug("{}: Forwarding pending transaction message {}", persistenceId(), message);
+
                         leader.tell(message, self());
                     }
                 }
@@ -760,9 +1026,13 @@ public class Shard extends RaftActor {
                 commitCoordinator.abortPendingTransactions("The transacton was aborted due to inflight leadership "
                         + "change and the leader address isn't available.", this);
             }
+        } else {
+            // We have become the leader, we need to reconstruct frontend state
+            knownFrontends = Verify.verifyNotNull(frontendMetadata.toLeaderState(this));
+            LOG.debug("{}: became leader with frontend state for {}", persistenceId(), knownFrontends.keySet());
         }
 
-        if (hasLeader && !isIsolatedLeader()) {
+        if (!isIsolatedLeader()) {
             messageRetrySupport.retryMessages();
         }
     }
@@ -780,14 +1050,49 @@ public class Shard extends RaftActor {
     @Override
     protected void pauseLeader(final Runnable operation) {
         LOG.debug("{}: In pauseLeader, operation: {}", persistenceId(), operation);
+        paused = true;
+
+        // Tell-based protocol can replay transaction state, so it is safe to blow it up when we are paused.
+        if (datastoreContext.isUseTellBasedProtocol()) {
+            knownFrontends.values().forEach(LeaderFrontendState::retire);
+            knownFrontends = ImmutableMap.of();
+        }
+
         store.setRunOnPendingTransactionsComplete(operation);
     }
 
+    @Override
+    protected void unpauseLeader() {
+        LOG.debug("{}: In unpauseLeader", persistenceId());
+        paused = false;
+
+        store.setRunOnPendingTransactionsComplete(null);
+
+        // Restore tell-based protocol state as if we were becoming the leader
+        knownFrontends = Verify.verifyNotNull(frontendMetadata.toLeaderState(this));
+    }
+
+    @Override
+    protected OnDemandRaftState.AbstractBuilder<?, ?> newOnDemandRaftStateBuilder() {
+        return OnDemandShardState.newBuilder().treeChangeListenerActors(treeChangeSupport.getListenerActors())
+                .commitCohortActors(store.getCohortActors());
+    }
+
     @Override
     public String persistenceId() {
         return this.name;
     }
 
+    @Override
+    public String journalPluginId() {
+        // This method may be invoked from super constructor (wonderful), hence we also need to handle the case of
+        // the field being uninitialized because our constructor is not finished.
+        if (datastoreContext != null && !datastoreContext.isPersistent()) {
+            return NON_PERSISTENT_JOURNAL_ID;
+        }
+        return super.journalPluginId();
+    }
+
     @VisibleForTesting
     ShardCommitCoordinator getCommitCoordinator() {
         return commitCoordinator;
@@ -812,21 +1117,22 @@ public class Shard extends RaftActor {
     }
 
     public abstract static class AbstractBuilder<T extends AbstractBuilder<T, S>, S extends Shard> {
-        private final Class<S> shardClass;
+        private final Class<? extends S> shardClass;
         private ShardIdentifier id;
         private Map<String, String> peerAddresses = Collections.emptyMap();
         private DatastoreContext datastoreContext;
-        private SchemaContext schemaContext;
+        private EffectiveModelContextProvider schemaContextProvider;
         private DatastoreSnapshot.ShardSnapshot restoreFromSnapshot;
-        private TipProducingDataTree dataTree;
+        private DataTree dataTree;
+
         private volatile boolean sealed;
 
-        protected AbstractBuilder(final Class<S> shardClass) {
+        protected AbstractBuilder(final Class<? extends S> shardClass) {
             this.shardClass = shardClass;
         }
 
         protected void checkSealed() {
-            Preconditions.checkState(!sealed, "Builder isalready sealed - further modifications are not allowed");
+            checkState(!sealed, "Builder isalready sealed - further modifications are not allowed");
         }
 
         @SuppressWarnings("unchecked")
@@ -852,9 +1158,9 @@ public class Shard extends RaftActor {
             return self();
         }
 
-        public T schemaContext(final SchemaContext newSchemaContext) {
+        public T schemaContextProvider(final EffectiveModelContextProvider newSchemaContextProvider) {
             checkSealed();
-            this.schemaContext = newSchemaContext;
+            this.schemaContextProvider = requireNonNull(newSchemaContextProvider);
             return self();
         }
 
@@ -864,7 +1170,7 @@ public class Shard extends RaftActor {
             return self();
         }
 
-        public T dataTree(final TipProducingDataTree newDataTree) {
+        public T dataTree(final DataTree newDataTree) {
             checkSealed();
             this.dataTree = newDataTree;
             return self();
@@ -882,15 +1188,15 @@ public class Shard extends RaftActor {
             return datastoreContext;
         }
 
-        public SchemaContext getSchemaContext() {
-            return schemaContext;
+        public EffectiveModelContext getSchemaContext() {
+            return Verify.verifyNotNull(schemaContextProvider.getEffectiveModelContext());
         }
 
         public DatastoreSnapshot.ShardSnapshot getRestoreFromSnapshot() {
             return restoreFromSnapshot;
         }
 
-        public TipProducingDataTree getDataTree() {
+        public DataTree getDataTree() {
             return dataTree;
         }
 
@@ -907,10 +1213,10 @@ public class Shard extends RaftActor {
         }
 
         protected void verify() {
-            Preconditions.checkNotNull(id, "id should not be null");
-            Preconditions.checkNotNull(peerAddresses, "peerAddresses should not be null");
-            Preconditions.checkNotNull(datastoreContext, "dataStoreContext should not be null");
-            Preconditions.checkNotNull(schemaContext, "schemaContext should not be null");
+            requireNonNull(id, "id should not be null");
+            requireNonNull(peerAddresses, "peerAddresses should not be null");
+            requireNonNull(datastoreContext, "dataStoreContext should not be null");
+            requireNonNull(schemaContextProvider, "schemaContextProvider should not be null");
         }
 
         public Props props() {
@@ -921,12 +1227,20 @@ public class Shard extends RaftActor {
     }
 
     public static class Builder extends AbstractBuilder<Builder, Shard> {
-        private Builder() {
-            super(Shard.class);
+        Builder() {
+            this(Shard.class);
+        }
+
+        Builder(final Class<? extends Shard> shardClass) {
+            super(shardClass);
         }
     }
 
     Ticker ticker() {
         return Ticker.systemTicker();
     }
+
+    void scheduleNextPendingTransaction() {
+        self().tell(RESUME_NEXT_PENDING_TRANSACTION, ActorRef.noSender());
+    }
 }