Enable testLeadershipTransferOnShutdown()
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / test / java / org / opendaylight / controller / cluster / datastore / DistributedDataStoreRemotingIntegrationTest.java
index 9c1103e60b2e4b8a641bdde277ae1e7aaf19f583..a516a292e3f1ee10e564df88d29fdc07a954d12c 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015 Brocade Communications Systems, Inc. and others.  All rights reserved.
+ * Copyright (c) 2015, 2017 Brocade Communications Systems, Inc. and others.  All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
@@ -7,48 +7,71 @@
  */
 package org.opendaylight.controller.cluster.datastore;
 
+import static org.awaitility.Awaitility.await;
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
-import static org.mockito.Matchers.any;
-import static org.mockito.Matchers.eq;
+import static org.junit.Assume.assumeTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.timeout;
 import static org.mockito.Mockito.verify;
+
 import akka.actor.ActorRef;
 import akka.actor.ActorSelection;
 import akka.actor.ActorSystem;
 import akka.actor.Address;
 import akka.actor.AddressFromURIString;
 import akka.cluster.Cluster;
+import akka.cluster.Member;
 import akka.dispatch.Futures;
-import akka.pattern.AskTimeoutException;
 import akka.pattern.Patterns;
-import akka.testkit.JavaTestKit;
-import com.google.common.base.Optional;
-import com.google.common.base.Supplier;
+import akka.testkit.javadsl.TestKit;
+import com.google.common.base.Stopwatch;
+import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.common.util.concurrent.Uninterruptibles;
 import com.typesafe.config.ConfigFactory;
-import java.math.BigInteger;
 import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.LinkedList;
+import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicLong;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
-import org.mockito.Mockito;
-import org.mockito.invocation.InvocationOnMock;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
 import org.mockito.stubbing.Answer;
+import org.opendaylight.controller.cluster.access.client.RequestTimeoutException;
+import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
+import org.opendaylight.controller.cluster.databroker.ClientBackedDataStore;
+import org.opendaylight.controller.cluster.databroker.ConcurrentDOMDataBroker;
+import org.opendaylight.controller.cluster.databroker.TestClientBackedDataStore;
 import org.opendaylight.controller.cluster.datastore.DatastoreContext.Builder;
-import org.opendaylight.controller.cluster.datastore.IntegrationTestKit.ShardStatsVerifier;
-import org.opendaylight.controller.cluster.datastore.MemberNode.RaftStateVerifier;
+import org.opendaylight.controller.cluster.datastore.TestShard.RequestFrontendMetadata;
+import org.opendaylight.controller.cluster.datastore.TestShard.StartDropMessages;
+import org.opendaylight.controller.cluster.datastore.TestShard.StopDropMessages;
 import org.opendaylight.controller.cluster.datastore.exceptions.NoShardLeaderException;
 import org.opendaylight.controller.cluster.datastore.exceptions.ShardLeaderNotRespondingException;
-import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardStats;
 import org.opendaylight.controller.cluster.datastore.messages.CommitTransactionReply;
 import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.GetShardDataTree;
@@ -56,39 +79,52 @@ import org.opendaylight.controller.cluster.datastore.messages.ReadyLocalTransact
 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
-import org.opendaylight.controller.cluster.raft.base.messages.ApplyJournalEntries;
+import org.opendaylight.controller.cluster.datastore.persisted.FrontendClientMetadata;
+import org.opendaylight.controller.cluster.datastore.persisted.FrontendShardDataTreeSnapshotMetadata;
+import org.opendaylight.controller.cluster.datastore.persisted.MetadataShardDataTreeSnapshot;
+import org.opendaylight.controller.cluster.datastore.persisted.ShardSnapshotState;
+import org.opendaylight.controller.cluster.datastore.utils.UnsignedLongBitmap;
+import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
+import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
+import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
+import org.opendaylight.controller.cluster.raft.messages.RequestVote;
+import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
+import org.opendaylight.controller.cluster.raft.persisted.Snapshot;
 import org.opendaylight.controller.cluster.raft.policy.DisableElectionsRaftPolicy;
 import org.opendaylight.controller.cluster.raft.utils.InMemoryJournal;
+import org.opendaylight.controller.cluster.raft.utils.InMemorySnapshotStore;
 import org.opendaylight.controller.md.cluster.datastore.model.CarsModel;
 import org.opendaylight.controller.md.cluster.datastore.model.PeopleModel;
 import org.opendaylight.controller.md.cluster.datastore.model.SchemaContextHelper;
 import org.opendaylight.controller.md.cluster.datastore.model.TestModel;
-import org.opendaylight.controller.md.sal.common.api.data.LogicalDatastoreType;
-import org.opendaylight.controller.md.sal.common.api.data.TransactionChainListener;
-import org.opendaylight.controller.md.sal.common.api.data.TransactionCommitFailedException;
-import org.opendaylight.controller.md.sal.dom.api.DOMDataWriteTransaction;
-import org.opendaylight.controller.md.sal.dom.api.DOMTransactionChain;
-import org.opendaylight.controller.sal.core.spi.data.DOMStore;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadTransaction;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadWriteTransaction;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreTransactionChain;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreWriteTransaction;
+import org.opendaylight.mdsal.common.api.LogicalDatastoreType;
+import org.opendaylight.mdsal.common.api.TransactionCommitFailedException;
+import org.opendaylight.mdsal.dom.api.DOMDataTreeWriteTransaction;
+import org.opendaylight.mdsal.dom.api.DOMTransactionChain;
+import org.opendaylight.mdsal.dom.api.DOMTransactionChainListener;
+import org.opendaylight.mdsal.dom.spi.store.DOMStore;
+import org.opendaylight.mdsal.dom.spi.store.DOMStoreReadTransaction;
+import org.opendaylight.mdsal.dom.spi.store.DOMStoreReadWriteTransaction;
+import org.opendaylight.mdsal.dom.spi.store.DOMStoreThreePhaseCommitCohort;
+import org.opendaylight.mdsal.dom.spi.store.DOMStoreTransactionChain;
+import org.opendaylight.mdsal.dom.spi.store.DOMStoreWriteTransaction;
+import org.opendaylight.yangtools.yang.common.Uint64;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
 import org.opendaylight.yangtools.yang.data.api.schema.ContainerNode;
 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
-import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
+import org.opendaylight.yangtools.yang.data.api.schema.SystemMapNode;
+import org.opendaylight.yangtools.yang.data.api.schema.builder.CollectionNodeBuilder;
 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
+import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeConfiguration;
 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeModification;
-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.data.impl.schema.ImmutableNodes;
-import org.opendaylight.yangtools.yang.data.impl.schema.builder.api.CollectionNodeBuilder;
 import org.opendaylight.yangtools.yang.data.impl.schema.builder.impl.ImmutableContainerNodeBuilder;
 import org.opendaylight.yangtools.yang.data.impl.schema.tree.InMemoryDataTreeFactory;
+import org.opendaylight.yangtools.yang.model.api.SchemaContext;
+import scala.collection.Set;
 import scala.concurrent.Await;
 import scala.concurrent.Future;
 import scala.concurrent.duration.FiniteDuration;
@@ -98,17 +134,33 @@ import scala.concurrent.duration.FiniteDuration;
  *
  * @author Thomas Pantelis
  */
-public class DistributedDataStoreRemotingIntegrationTest {
+@RunWith(Parameterized.class)
+public class DistributedDataStoreRemotingIntegrationTest extends AbstractTest {
+
+    @Parameters(name = "{0}")
+    public static Collection<Object[]> data() {
+        return Arrays.asList(new Object[][] {
+                { TestDistributedDataStore.class, 7}, { TestClientBackedDataStore.class, 12 }
+        });
+    }
+
+    @Parameter(0)
+    public Class<? extends AbstractDataStore> testParameter;
+    @Parameter(1)
+    public int commitTimeout;
 
     private static final String[] CARS_AND_PEOPLE = {"cars", "people"};
     private static final String[] CARS = {"cars"};
 
-    private static final Address MEMBER_1_ADDRESS = AddressFromURIString.parse("akka.tcp://cluster-test@127.0.0.1:2558");
-    private static final Address MEMBER_2_ADDRESS = AddressFromURIString.parse("akka.tcp://cluster-test@127.0.0.1:2559");
+    private static final Address MEMBER_1_ADDRESS = AddressFromURIString.parse(
+            "akka://cluster-test@127.0.0.1:2558");
+    private static final Address MEMBER_2_ADDRESS = AddressFromURIString.parse(
+            "akka://cluster-test@127.0.0.1:2559");
 
     private static final String MODULE_SHARDS_CARS_ONLY_1_2 = "module-shards-cars-member-1-and-2.conf";
     private static final String MODULE_SHARDS_CARS_PEOPLE_1_2 = "module-shards-member1-and-2.conf";
     private static final String MODULE_SHARDS_CARS_PEOPLE_1_2_3 = "module-shards-member1-and-2-and-3.conf";
+    private static final String MODULE_SHARDS_CARS_1_2_3 = "module-shards-cars-member-1-and-2-and-3.conf";
 
     private ActorSystem leaderSystem;
     private ActorSystem followerSystem;
@@ -118,16 +170,21 @@ public class DistributedDataStoreRemotingIntegrationTest {
             DatastoreContext.newBuilder().shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(2);
 
     private final DatastoreContext.Builder followerDatastoreContextBuilder =
-            DatastoreContext.newBuilder().shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(5).
-                customRaftPolicyImplementation(DisableElectionsRaftPolicy.class.getName());
+            DatastoreContext.newBuilder().shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(5)
+                .customRaftPolicyImplementation(DisableElectionsRaftPolicy.class.getName());
+    private final TransactionIdentifier tx1 = nextTransactionId();
+    private final TransactionIdentifier tx2 = nextTransactionId();
 
-    private DistributedDataStore followerDistributedDataStore;
-    private DistributedDataStore leaderDistributedDataStore;
+    private AbstractDataStore followerDistributedDataStore;
+    private AbstractDataStore leaderDistributedDataStore;
     private IntegrationTestKit followerTestKit;
     private IntegrationTestKit leaderTestKit;
 
     @Before
     public void setUp() {
+        InMemoryJournal.clear();
+        InMemorySnapshotStore.clear();
+
         leaderSystem = ActorSystem.create("cluster-test", ConfigFactory.load().getConfig("Member1"));
         Cluster.get(leaderSystem).join(MEMBER_1_ADDRESS);
 
@@ -140,61 +197,83 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
     @After
     public void tearDown() {
-        JavaTestKit.shutdownActorSystem(leaderSystem);
-        JavaTestKit.shutdownActorSystem(followerSystem);
-        JavaTestKit.shutdownActorSystem(follower2System);
+        if (followerDistributedDataStore != null) {
+            leaderDistributedDataStore.close();
+        }
+        if (leaderDistributedDataStore != null) {
+            leaderDistributedDataStore.close();
+        }
+
+        TestKit.shutdownActorSystem(leaderSystem, true);
+        TestKit.shutdownActorSystem(followerSystem, true);
+        TestKit.shutdownActorSystem(follower2System,true);
+
+        InMemoryJournal.clear();
+        InMemorySnapshotStore.clear();
     }
 
-    private void initDatastoresWithCars(String type) {
+    private void initDatastoresWithCars(final String type) throws Exception {
         initDatastores(type, MODULE_SHARDS_CARS_ONLY_1_2, CARS);
     }
 
-    private void initDatastoresWithCarsAndPeople(String type) {
+    private void initDatastoresWithCarsAndPeople(final String type) throws Exception {
         initDatastores(type, MODULE_SHARDS_CARS_PEOPLE_1_2, CARS_AND_PEOPLE);
     }
 
-    private void initDatastores(String type, String moduleShardsConfig, String[] shards) {
-        leaderTestKit = new IntegrationTestKit(leaderSystem, leaderDatastoreContextBuilder);
+    private void initDatastores(final String type, final String moduleShardsConfig, final String[] shards)
+            throws Exception {
+        initDatastores(type, moduleShardsConfig, shards, leaderDatastoreContextBuilder,
+                followerDatastoreContextBuilder);
+    }
+
+    private void initDatastores(final String type, final String moduleShardsConfig, final String[] shards,
+            final DatastoreContext.Builder leaderBuilder, final DatastoreContext.Builder followerBuilder)
+                    throws Exception {
+        leaderTestKit = new IntegrationTestKit(leaderSystem, leaderBuilder, commitTimeout);
+
+        leaderDistributedDataStore = leaderTestKit.setupAbstractDataStore(
+                testParameter, type, moduleShardsConfig, false, shards);
 
-        leaderDistributedDataStore = leaderTestKit.setupDistributedDataStore(type, moduleShardsConfig, false, shards);
+        followerTestKit = new IntegrationTestKit(followerSystem, followerBuilder, commitTimeout);
+        followerDistributedDataStore = followerTestKit.setupAbstractDataStore(
+                testParameter, type, moduleShardsConfig, false, shards);
 
-        followerTestKit = new IntegrationTestKit(followerSystem, followerDatastoreContextBuilder);
-        followerDistributedDataStore = followerTestKit.setupDistributedDataStore(type, moduleShardsConfig, false, shards);
+        leaderTestKit.waitUntilLeader(leaderDistributedDataStore.getActorUtils(), shards);
 
-        leaderTestKit.waitUntilLeader(leaderDistributedDataStore.getActorContext(), shards);
+        leaderTestKit.waitForMembersUp("member-2");
+        followerTestKit.waitForMembersUp("member-1");
     }
 
-    private static void verifyCars(DOMStoreReadTransaction readTx, MapEntryNode... entries) throws Exception {
-        Optional<NormalizedNode<?, ?>> optional = readTx.read(CarsModel.CAR_LIST_PATH).get(5, TimeUnit.SECONDS);
-        assertEquals("isPresent", true, optional.isPresent());
+    private static void verifyCars(final DOMStoreReadTransaction readTx, final MapEntryNode... entries)
+            throws Exception {
+        final Optional<NormalizedNode> optional = readTx.read(CarsModel.CAR_LIST_PATH).get(5, TimeUnit.SECONDS);
+        assertTrue("isPresent", optional.isPresent());
 
-        CollectionNodeBuilder<MapEntryNode, MapNode> listBuilder = ImmutableNodes.mapNodeBuilder(CarsModel.CAR_QNAME);
-        for(NormalizedNode<?, ?> entry: entries) {
+        final CollectionNodeBuilder<MapEntryNode, SystemMapNode> listBuilder = ImmutableNodes.mapNodeBuilder(
+                CarsModel.CAR_QNAME);
+        for (final NormalizedNode entry: entries) {
             listBuilder.withChild((MapEntryNode) entry);
         }
 
         assertEquals("Car list node", listBuilder.build(), optional.get());
     }
 
-    private static void verifyNode(DOMStoreReadTransaction readTx, YangInstanceIdentifier path, NormalizedNode<?, ?> expNode)
-            throws Exception {
-        Optional<NormalizedNode<?, ?>> optional = readTx.read(path).get(5, TimeUnit.SECONDS);
-        assertEquals("isPresent", true, optional.isPresent());
-        assertEquals("Data node", expNode, optional.get());
+    private static void verifyNode(final DOMStoreReadTransaction readTx, final YangInstanceIdentifier path,
+            final NormalizedNode expNode) throws Exception {
+        assertEquals(Optional.of(expNode), readTx.read(path).get(5, TimeUnit.SECONDS));
     }
 
-    private static void verifyExists(DOMStoreReadTransaction readTx, YangInstanceIdentifier path) throws Exception {
-        Boolean exists = readTx.exists(path).get(5, TimeUnit.SECONDS);
-        assertEquals("exists", true, exists);
+    private static void verifyExists(final DOMStoreReadTransaction readTx, final YangInstanceIdentifier path)
+            throws Exception {
+        assertEquals("exists", Boolean.TRUE, readTx.exists(path).get(5, TimeUnit.SECONDS));
     }
 
     @Test
     public void testWriteTransactionWithSingleShard() throws Exception {
-        String testName = "testWriteTransactionWithSingleShard";
+        final String testName = "testWriteTransactionWithSingleShard";
         initDatastoresWithCars(testName);
 
-        String followerCarShardName = "member-2-shard-cars-" + testName;
-        InMemoryJournal.addWriteMessagesCompleteLatch(followerCarShardName, 2, ApplyJournalEntries.class );
+        final String followerCarShardName = "member-2-shard-cars-" + testName;
 
         DOMStoreWriteTransaction writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
         assertNotNull("newWriteOnlyTransaction returned null", writeTx);
@@ -202,12 +281,12 @@ public class DistributedDataStoreRemotingIntegrationTest {
         writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
         writeTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
-        YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
+        final MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
+        final YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
         writeTx.merge(car1Path, car1);
 
-        MapEntryNode car2 = CarsModel.newCarEntry("sportage", BigInteger.valueOf(25000));
-        YangInstanceIdentifier car2Path = CarsModel.newCarPath("sportage");
+        final MapEntryNode car2 = CarsModel.newCarEntry("sportage", Uint64.valueOf(25000));
+        final YangInstanceIdentifier car2Path = CarsModel.newCarPath("sportage");
         writeTx.merge(car2Path, car2);
 
         followerTestKit.doCommit(writeTx.ready());
@@ -232,38 +311,178 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
         // Re-instate the follower member 2 as a single-node to verify replication and recovery.
 
-        InMemoryJournal.waitForWriteMessagesComplete(followerCarShardName);
+        // The following is a bit tricky. Before we reinstate the follower we need to ensure it has persisted and
+        // applied and all the log entries from the leader. Since we've verified the car data above we know that
+        // all the transactions have been applied on the leader so we first read and capture its lastAppliedIndex.
+        final AtomicLong leaderLastAppliedIndex = new AtomicLong();
+        IntegrationTestKit.verifyShardState(leaderDistributedDataStore, CARS[0],
+            state -> leaderLastAppliedIndex.set(state.getLastApplied()));
+
+        // Now we need to make sure the follower has persisted the leader's lastAppliedIndex via ApplyJournalEntries.
+        // However we don't know exactly how many ApplyJournalEntries messages there will be as it can differ between
+        // the tell-based and ask-based front-ends. For ask-based there will be exactly 2 ApplyJournalEntries but
+        // tell-based persists additional payloads which could be replicated and applied in a batch resulting in
+        // either 2 or 3 ApplyJournalEntries. To handle this we read the follower's persisted ApplyJournalEntries
+        // until we find the one that encompasses the leader's lastAppliedIndex.
+        Stopwatch sw = Stopwatch.createStarted();
+        boolean done = false;
+        while (!done) {
+            final List<ApplyJournalEntries> entries = InMemoryJournal.get(followerCarShardName,
+                    ApplyJournalEntries.class);
+            for (ApplyJournalEntries aje: entries) {
+                if (aje.getToIndex() >= leaderLastAppliedIndex.get()) {
+                    done = true;
+                    break;
+                }
+            }
 
-        JavaTestKit.shutdownActorSystem(leaderSystem, null, true);
-        JavaTestKit.shutdownActorSystem(followerSystem, null, true);
+            assertTrue("Follower did not persist ApplyJournalEntries containing leader's lastAppliedIndex "
+                    + leaderLastAppliedIndex + ". Entries persisted: " + entries, sw.elapsed(TimeUnit.SECONDS) <= 5);
 
-        ActorSystem newSystem = ActorSystem.create("reinstated-member2", ConfigFactory.load().getConfig("Member2"));
+            Uninterruptibles.sleepUninterruptibly(50, TimeUnit.MILLISECONDS);
+        }
 
-        DistributedDataStore member2Datastore = new IntegrationTestKit(newSystem, leaderDatastoreContextBuilder).
-                setupDistributedDataStore(testName, "module-shards-member2", true, CARS_AND_PEOPLE);
+        TestKit.shutdownActorSystem(leaderSystem, true);
+        TestKit.shutdownActorSystem(followerSystem, true);
 
-        verifyCars(member2Datastore.newReadOnlyTransaction(), car2);
+        final ActorSystem newSystem = newActorSystem("reinstated-member2", "Member2");
 
-        JavaTestKit.shutdownActorSystem(newSystem);
+        try (AbstractDataStore member2Datastore = new IntegrationTestKit(newSystem, leaderDatastoreContextBuilder,
+                commitTimeout)
+                .setupAbstractDataStore(testParameter, testName, "module-shards-member2", true, CARS)) {
+            verifyCars(member2Datastore.newReadOnlyTransaction(), car2);
+        }
+    }
+
+    @Test
+    public void testSingleTransactionsWritesInQuickSuccession() throws Exception {
+        initDatastoresWithCars("testSingleTransactionsWritesInQuickSuccession");
+
+        final DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
+
+        DOMStoreWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
+        writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+        writeTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
+        followerTestKit.doCommit(writeTx.ready());
+
+        int numCars = 5;
+        for (int i = 0; i < numCars; i++) {
+            writeTx = txChain.newWriteOnlyTransaction();
+            writeTx.write(CarsModel.newCarPath("car" + i), CarsModel.newCarEntry("car" + i, Uint64.valueOf(20000)));
+            followerTestKit.doCommit(writeTx.ready());
+
+            try (var tx = txChain.newReadOnlyTransaction()) {
+                tx.read(CarsModel.BASE_PATH).get();
+            }
+        }
+
+        // wait to let the shard catch up with purged
+        await("Range set leak test").atMost(5, TimeUnit.SECONDS)
+                .pollInterval(500, TimeUnit.MILLISECONDS)
+                .untilAsserted(() -> {
+                    final var localShard = leaderDistributedDataStore.getActorUtils().findLocalShard("cars")
+                        .orElseThrow();
+                    final var frontendMetadata =
+                        (FrontendShardDataTreeSnapshotMetadata) leaderDistributedDataStore.getActorUtils()
+                            .executeOperation(localShard, new RequestFrontendMetadata());
+
+                    final var clientMeta = frontendMetadata.getClients().get(0);
+                    if (leaderDistributedDataStore.getActorUtils().getDatastoreContext().isUseTellBasedProtocol()) {
+                        assertTellClientMetadata(clientMeta, numCars * 2);
+                    } else {
+                        assertAskClientMetadata(clientMeta);
+                    }
+                });
+
+        try (var tx = txChain.newReadOnlyTransaction()) {
+            final var body = tx.read(CarsModel.CAR_LIST_PATH).get(5, TimeUnit.SECONDS).orElseThrow().body();
+            assertThat(body, instanceOf(Collection.class));
+            assertEquals(numCars, ((Collection<?>) body).size());
+        }
+    }
+
+    private static void assertAskClientMetadata(final FrontendClientMetadata clientMeta) {
+        // ask based should track no metadata
+        assertEquals(List.of(), clientMeta.getCurrentHistories());
+    }
+
+    private static void assertTellClientMetadata(final FrontendClientMetadata clientMeta, final long lastPurged) {
+        final var iterator = clientMeta.getCurrentHistories().iterator();
+        var metadata = iterator.next();
+        while (iterator.hasNext() && metadata.getHistoryId() != 1) {
+            metadata = iterator.next();
+        }
+
+        assertEquals(UnsignedLongBitmap.of(), metadata.getClosedTransactions());
+        assertEquals("[[0.." + lastPurged + "]]", metadata.getPurgedTransactions().ranges().toString());
+    }
+
+    @Test
+    public void testCloseTransactionMetadataLeak() throws Exception {
+        // FIXME: CONTROLLER-2016: ask-based frontend triggers this:
+        //
+        // java.lang.IllegalStateException: Previous transaction
+        //            member-2-datastore-testCloseTransactionMetadataLeak-fe-0-chn-1-txn-1-0 is not ready yet
+        //        at org.opendaylight.controller.cluster.datastore.TransactionChainProxy$Allocated.checkReady()
+        //        at org.opendaylight.controller.cluster.datastore.TransactionChainProxy.newReadOnlyTransaction()
+        assumeTrue(testParameter.isAssignableFrom(ClientBackedDataStore.class));
+
+        initDatastoresWithCars("testCloseTransactionMetadataLeak");
+
+        final DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
+
+        DOMStoreWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
+        writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+        writeTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
+        followerTestKit.doCommit(writeTx.ready());
+
+        int numCars = 5;
+        for (int i = 0; i < numCars; i++) {
+            try (var tx = txChain.newWriteOnlyTransaction()) {
+                // Empty on purpose
+            }
+
+            try (var tx = txChain.newReadOnlyTransaction()) {
+                tx.read(CarsModel.BASE_PATH).get();
+            }
+        }
+
+        // wait to let the shard catch up with purged
+        await("wait for purges to settle").atMost(5, TimeUnit.SECONDS)
+                .pollInterval(500, TimeUnit.MILLISECONDS)
+                .untilAsserted(() -> {
+                    final var localShard = leaderDistributedDataStore.getActorUtils().findLocalShard("cars")
+                        .orElseThrow();
+                    final var frontendMetadata =
+                            (FrontendShardDataTreeSnapshotMetadata) leaderDistributedDataStore.getActorUtils()
+                                    .executeOperation(localShard, new RequestFrontendMetadata());
+
+                    final var clientMeta = frontendMetadata.getClients().get(0);
+                    if (leaderDistributedDataStore.getActorUtils().getDatastoreContext().isUseTellBasedProtocol()) {
+                        assertTellClientMetadata(clientMeta, numCars * 2);
+                    } else {
+                        assertAskClientMetadata(clientMeta);
+                    }
+                });
     }
 
     @Test
     public void testReadWriteTransactionWithSingleShard() throws Exception {
         initDatastoresWithCars("testReadWriteTransactionWithSingleShard");
 
-        DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
         assertNotNull("newReadWriteTransaction returned null", rwTx);
 
         rwTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
         rwTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
+        final MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
         rwTx.merge(CarsModel.newCarPath("optima"), car1);
 
         verifyCars(rwTx, car1);
 
-        MapEntryNode car2 = CarsModel.newCarEntry("sportage", BigInteger.valueOf(25000));
-        YangInstanceIdentifier car2Path = CarsModel.newCarPath("sportage");
+        final MapEntryNode car2 = CarsModel.newCarEntry("sportage", Uint64.valueOf(25000));
+        final YangInstanceIdentifier car2Path = CarsModel.newCarPath("sportage");
         rwTx.merge(car2Path, car2);
 
         verifyExists(rwTx, car2Path);
@@ -277,20 +496,20 @@ public class DistributedDataStoreRemotingIntegrationTest {
     public void testWriteTransactionWithMultipleShards() throws Exception {
         initDatastoresWithCarsAndPeople("testWriteTransactionWithMultipleShards");
 
-        DOMStoreWriteTransaction writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
+        final DOMStoreWriteTransaction writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
         assertNotNull("newWriteOnlyTransaction returned null", writeTx);
 
-        YangInstanceIdentifier carsPath = CarsModel.BASE_PATH;
-        NormalizedNode<?, ?> carsNode = CarsModel.emptyContainer();
+        final YangInstanceIdentifier carsPath = CarsModel.BASE_PATH;
+        final NormalizedNode carsNode = CarsModel.emptyContainer();
         writeTx.write(carsPath, carsNode);
 
-        YangInstanceIdentifier peoplePath = PeopleModel.BASE_PATH;
-        NormalizedNode<?, ?> peopleNode = PeopleModel.emptyContainer();
+        final YangInstanceIdentifier peoplePath = PeopleModel.BASE_PATH;
+        final NormalizedNode peopleNode = PeopleModel.emptyContainer();
         writeTx.write(peoplePath, peopleNode);
 
         followerTestKit.doCommit(writeTx.ready());
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+        final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
 
         verifyNode(readTx, carsPath, carsNode);
         verifyNode(readTx, peoplePath, peopleNode);
@@ -300,20 +519,20 @@ public class DistributedDataStoreRemotingIntegrationTest {
     public void testReadWriteTransactionWithMultipleShards() throws Exception {
         initDatastoresWithCarsAndPeople("testReadWriteTransactionWithMultipleShards");
 
-        DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
         assertNotNull("newReadWriteTransaction returned null", rwTx);
 
-        YangInstanceIdentifier carsPath = CarsModel.BASE_PATH;
-        NormalizedNode<?, ?> carsNode = CarsModel.emptyContainer();
+        final YangInstanceIdentifier carsPath = CarsModel.BASE_PATH;
+        final NormalizedNode carsNode = CarsModel.emptyContainer();
         rwTx.write(carsPath, carsNode);
 
-        YangInstanceIdentifier peoplePath = PeopleModel.BASE_PATH;
-        NormalizedNode<?, ?> peopleNode = PeopleModel.emptyContainer();
+        final YangInstanceIdentifier peoplePath = PeopleModel.BASE_PATH;
+        final NormalizedNode peopleNode = PeopleModel.emptyContainer();
         rwTx.write(peoplePath, peopleNode);
 
         followerTestKit.doCommit(rwTx.ready());
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+        final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
 
         verifyNode(readTx, carsPath, carsNode);
         verifyNode(readTx, peoplePath, peopleNode);
@@ -323,16 +542,16 @@ public class DistributedDataStoreRemotingIntegrationTest {
     public void testTransactionChainWithSingleShard() throws Exception {
         initDatastoresWithCars("testTransactionChainWithSingleShard");
 
-        DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
+        final DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
 
         // Add the top-level cars container with write-only.
 
-        DOMStoreWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
+        final DOMStoreWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
         assertNotNull("newWriteOnlyTransaction returned null", writeTx);
 
         writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
-        writeTx.ready();
+        final DOMStoreThreePhaseCommitCohort writeTxReady = writeTx.ready();
 
         // Verify the top-level cars container with read-only.
 
@@ -340,25 +559,27 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
         // Perform car operations with read-write.
 
-        DOMStoreReadWriteTransaction rwTx = txChain.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction rwTx = txChain.newReadWriteTransaction();
 
         verifyNode(rwTx, CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
         rwTx.merge(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
-        YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
+        final MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
+        final YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
         rwTx.write(car1Path, car1);
 
         verifyExists(rwTx, car1Path);
 
         verifyCars(rwTx, car1);
 
-        MapEntryNode car2 = CarsModel.newCarEntry("sportage", BigInteger.valueOf(25000));
+        final MapEntryNode car2 = CarsModel.newCarEntry("sportage", Uint64.valueOf(25000));
         rwTx.merge(CarsModel.newCarPath("sportage"), car2);
 
         rwTx.delete(car1Path);
 
+        followerTestKit.doCommit(writeTxReady);
+
         followerTestKit.doCommit(rwTx.ready());
 
         txChain.close();
@@ -367,10 +588,10 @@ public class DistributedDataStoreRemotingIntegrationTest {
     }
 
     @Test
-    public void testTransactionChainWithMultipleShards() throws Exception{
+    public void testTransactionChainWithMultipleShards() throws Exception {
         initDatastoresWithCarsAndPeople("testTransactionChainWithMultipleShards");
 
-        DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
+        final DOMStoreTransactionChain txChain = followerDistributedDataStore.createTransactionChain();
 
         DOMStoreWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
         assertNotNull("newWriteOnlyTransaction returned null", writeTx);
@@ -383,70 +604,61 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
         followerTestKit.doCommit(writeTx.ready());
 
-        DOMStoreReadWriteTransaction readWriteTx = txChain.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction readWriteTx = txChain.newReadWriteTransaction();
 
-        MapEntryNode car = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
-        YangInstanceIdentifier carPath = CarsModel.newCarPath("optima");
+        final MapEntryNode car = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
+        final YangInstanceIdentifier carPath = CarsModel.newCarPath("optima");
         readWriteTx.write(carPath, car);
 
-        MapEntryNode person = PeopleModel.newPersonEntry("jack");
-        YangInstanceIdentifier personPath = PeopleModel.newPersonPath("jack");
+        final MapEntryNode person = PeopleModel.newPersonEntry("jack");
+        final YangInstanceIdentifier personPath = PeopleModel.newPersonPath("jack");
         readWriteTx.merge(personPath, person);
 
-        Optional<NormalizedNode<?, ?>> optional = readWriteTx.read(carPath).get(5, TimeUnit.SECONDS);
-        assertEquals("isPresent", true, optional.isPresent());
-        assertEquals("Data node", car, optional.get());
-
-        optional = readWriteTx.read(personPath).get(5, TimeUnit.SECONDS);
-        assertEquals("isPresent", true, optional.isPresent());
-        assertEquals("Data node", person, optional.get());
+        assertEquals(Optional.of(car), readWriteTx.read(carPath).get(5, TimeUnit.SECONDS));
+        assertEquals(Optional.of(person), readWriteTx.read(personPath).get(5, TimeUnit.SECONDS));
 
-        DOMStoreThreePhaseCommitCohort cohort2 = readWriteTx.ready();
+        final DOMStoreThreePhaseCommitCohort cohort2 = readWriteTx.ready();
 
         writeTx = txChain.newWriteOnlyTransaction();
 
         writeTx.delete(personPath);
 
-        DOMStoreThreePhaseCommitCohort cohort3 = writeTx.ready();
+        final DOMStoreThreePhaseCommitCohort cohort3 = writeTx.ready();
 
         followerTestKit.doCommit(cohort2);
         followerTestKit.doCommit(cohort3);
 
         txChain.close();
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+        final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
         verifyCars(readTx, car);
 
-        optional = readTx.read(personPath).get(5, TimeUnit.SECONDS);
-        assertEquals("isPresent", false, optional.isPresent());
+        assertEquals(Optional.empty(), readTx.read(personPath).get(5, TimeUnit.SECONDS));
     }
 
     @Test
     public void testChainedTransactionFailureWithSingleShard() throws Exception {
         initDatastoresWithCars("testChainedTransactionFailureWithSingleShard");
 
-        ConcurrentDOMDataBroker broker = new ConcurrentDOMDataBroker(
+        final ConcurrentDOMDataBroker broker = new ConcurrentDOMDataBroker(
                 ImmutableMap.<LogicalDatastoreType, DOMStore>builder().put(
                         LogicalDatastoreType.CONFIGURATION, followerDistributedDataStore).build(),
                         MoreExecutors.directExecutor());
 
-        TransactionChainListener listener = Mockito.mock(TransactionChainListener.class);
-        DOMTransactionChain txChain = broker.createTransactionChain(listener);
+        final DOMTransactionChainListener listener = mock(DOMTransactionChainListener.class);
+        final DOMTransactionChain txChain = broker.createTransactionChain(listener);
 
-        DOMDataWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
+        final DOMDataTreeWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
 
-        ContainerNode invalidData = ImmutableContainerNodeBuilder.create().withNodeIdentifier(
-                new YangInstanceIdentifier.NodeIdentifier(CarsModel.BASE_QNAME)).
-                    withChild(ImmutableNodes.leafNode(TestModel.JUNK_QNAME, "junk")).build();
+        final ContainerNode invalidData = ImmutableContainerNodeBuilder.create().withNodeIdentifier(
+                new YangInstanceIdentifier.NodeIdentifier(CarsModel.BASE_QNAME))
+                    .withChild(ImmutableNodes.leafNode(TestModel.JUNK_QNAME, "junk")).build();
 
         writeTx.merge(LogicalDatastoreType.CONFIGURATION, CarsModel.BASE_PATH, invalidData);
 
-        try {
-            writeTx.submit().checkedGet(5, TimeUnit.SECONDS);
-            fail("Expected TransactionCommitFailedException");
-        } catch (TransactionCommitFailedException e) {
-            // Expected
-        }
+        final var ex = assertThrows(ExecutionException.class, () -> writeTx.commit().get(5, TimeUnit.SECONDS))
+            .getCause();
+        assertThat(ex, instanceOf(TransactionCommitFailedException.class));
 
         verify(listener, timeout(5000)).onTransactionChainFailed(eq(txChain), eq(writeTx), any(Throwable.class));
 
@@ -458,32 +670,29 @@ public class DistributedDataStoreRemotingIntegrationTest {
     public void testChainedTransactionFailureWithMultipleShards() throws Exception {
         initDatastoresWithCarsAndPeople("testChainedTransactionFailureWithMultipleShards");
 
-        ConcurrentDOMDataBroker broker = new ConcurrentDOMDataBroker(
+        final ConcurrentDOMDataBroker broker = new ConcurrentDOMDataBroker(
                 ImmutableMap.<LogicalDatastoreType, DOMStore>builder().put(
                         LogicalDatastoreType.CONFIGURATION, followerDistributedDataStore).build(),
                         MoreExecutors.directExecutor());
 
-        TransactionChainListener listener = Mockito.mock(TransactionChainListener.class);
-        DOMTransactionChain txChain = broker.createTransactionChain(listener);
+        final DOMTransactionChainListener listener = mock(DOMTransactionChainListener.class);
+        final DOMTransactionChain txChain = broker.createTransactionChain(listener);
 
-        DOMDataWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
+        final DOMDataTreeWriteTransaction writeTx = txChain.newWriteOnlyTransaction();
 
         writeTx.put(LogicalDatastoreType.CONFIGURATION, PeopleModel.BASE_PATH, PeopleModel.emptyContainer());
 
-        ContainerNode invalidData = ImmutableContainerNodeBuilder.create().withNodeIdentifier(
-                new YangInstanceIdentifier.NodeIdentifier(CarsModel.BASE_QNAME)).
-                    withChild(ImmutableNodes.leafNode(TestModel.JUNK_QNAME, "junk")).build();
+        final ContainerNode invalidData = ImmutableContainerNodeBuilder.create().withNodeIdentifier(
+                new YangInstanceIdentifier.NodeIdentifier(CarsModel.BASE_QNAME))
+                    .withChild(ImmutableNodes.leafNode(TestModel.JUNK_QNAME, "junk")).build();
 
         // Note that merge will validate the data and fail but put succeeds b/c deep validation is not
         // done for put for performance reasons.
         writeTx.merge(LogicalDatastoreType.CONFIGURATION, CarsModel.BASE_PATH, invalidData);
 
-        try {
-            writeTx.submit().checkedGet(5, TimeUnit.SECONDS);
-            fail("Expected TransactionCommitFailedException");
-        } catch (TransactionCommitFailedException e) {
-            // Expected
-        }
+        final var ex = assertThrows(ExecutionException.class, () -> writeTx.commit().get(5, TimeUnit.SECONDS))
+            .getCause();
+        assertThat(ex, instanceOf(TransactionCommitFailedException.class));
 
         verify(listener, timeout(5000)).onTransactionChainFailed(eq(txChain), eq(writeTx), any(Throwable.class));
 
@@ -493,11 +702,12 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
     @Test
     public void testSingleShardTransactionsWithLeaderChanges() throws Exception {
-        String testName = "testSingleShardTransactionsWithLeaderChanges";
+        followerDatastoreContextBuilder.backendAlivenessTimerIntervalInSeconds(2);
+        final String testName = "testSingleShardTransactionsWithLeaderChanges";
         initDatastoresWithCars(testName);
 
-        String followerCarShardName = "member-2-shard-cars-" + testName;
-        InMemoryJournal.addWriteMessagesCompleteLatch(followerCarShardName, 1, ApplyJournalEntries.class );
+        final String followerCarShardName = "member-2-shard-cars-" + testName;
+        InMemoryJournal.addWriteMessagesCompleteLatch(followerCarShardName, 1, ApplyJournalEntries.class);
 
         // Write top-level car container from the follower so it uses a remote Tx.
 
@@ -512,47 +722,53 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
         // Switch the leader to the follower
 
-        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder.
-                shardElectionTimeoutFactor(1).customRaftPolicyImplementation(null));
+        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder
+                .shardElectionTimeoutFactor(1).customRaftPolicyImplementation(null));
 
-        JavaTestKit.shutdownActorSystem(leaderSystem, null, true);
+        TestKit.shutdownActorSystem(leaderSystem, true);
+        Cluster.get(followerSystem).leave(MEMBER_1_ADDRESS);
 
-        followerTestKit.waitUntilNoLeader(followerDistributedDataStore.getActorContext(), CARS);
+        followerTestKit.waitUntilNoLeader(followerDistributedDataStore.getActorUtils(), CARS);
 
         leaderSystem = ActorSystem.create("cluster-test", ConfigFactory.load().getConfig("Member1"));
         Cluster.get(leaderSystem).join(MEMBER_2_ADDRESS);
 
-        DatastoreContext.Builder newMember1Builder = DatastoreContext.newBuilder().
-                shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(5);
-        IntegrationTestKit newMember1TestKit = new IntegrationTestKit(leaderSystem, newMember1Builder);
-        newMember1TestKit.setupDistributedDataStore(testName, MODULE_SHARDS_CARS_ONLY_1_2, false, CARS);
+        final DatastoreContext.Builder newMember1Builder = DatastoreContext.newBuilder()
+                .shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(5);
+        IntegrationTestKit newMember1TestKit = new IntegrationTestKit(leaderSystem, newMember1Builder, commitTimeout);
 
-        followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorContext(), CARS);
+        try (AbstractDataStore ds =
+                newMember1TestKit.setupAbstractDataStore(
+                        testParameter, testName, MODULE_SHARDS_CARS_ONLY_1_2, false, CARS)) {
 
-        // Write a car entry to the new leader - should switch to local Tx
+            followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorUtils(), CARS);
 
-        writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
+            // Write a car entry to the new leader - should switch to local Tx
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
-        YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
-        writeTx.merge(car1Path, car1);
+            writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
 
-        followerTestKit.doCommit(writeTx.ready());
+            MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
+            YangInstanceIdentifier car1Path = CarsModel.newCarPath("optima");
+            writeTx.merge(car1Path, car1);
 
-        verifyCars(followerDistributedDataStore.newReadOnlyTransaction(), car1);
+            followerTestKit.doCommit(writeTx.ready());
+
+            verifyCars(followerDistributedDataStore.newReadOnlyTransaction(), car1);
+        }
     }
 
     @SuppressWarnings("unchecked")
     @Test
     public void testReadyLocalTransactionForwardedToLeader() throws Exception {
         initDatastoresWithCars("testReadyLocalTransactionForwardedToLeader");
-        followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorContext(), "cars");
+        followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorUtils(), "cars");
 
-        Optional<ActorRef> carsFollowerShard = followerDistributedDataStore.getActorContext().findLocalShard("cars");
-        assertEquals("Cars follower shard found", true, carsFollowerShard.isPresent());
+        final Optional<ActorRef> carsFollowerShard =
+                followerDistributedDataStore.getActorUtils().findLocalShard("cars");
+        assertTrue("Cars follower shard found", carsFollowerShard.isPresent());
 
-        TipProducingDataTree dataTree = InMemoryDataTreeFactory.getInstance().create(TreeType.OPERATIONAL);
-        dataTree.setSchemaContext(SchemaContextHelper.full());
+        final DataTree dataTree = new InMemoryDataTreeFactory().create(
+            DataTreeConfiguration.DEFAULT_OPERATIONAL, SchemaContextHelper.full());
 
         // Send a tx with immediate commit.
 
@@ -560,15 +776,15 @@ public class DistributedDataStoreRemotingIntegrationTest {
         new WriteModification(CarsModel.BASE_PATH, CarsModel.emptyContainer()).apply(modification);
         new MergeModification(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode()).apply(modification);
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
+        final MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
         new WriteModification(CarsModel.newCarPath("optima"), car1).apply(modification);
         modification.ready();
 
-        ReadyLocalTransaction readyLocal = new ReadyLocalTransaction("tx-1" , modification, true);
+        ReadyLocalTransaction readyLocal = new ReadyLocalTransaction(tx1 , modification, true, Optional.empty());
 
         carsFollowerShard.get().tell(readyLocal, followerTestKit.getRef());
         Object resp = followerTestKit.expectMsgClass(Object.class);
-        if(resp instanceof akka.actor.Status.Failure) {
+        if (resp instanceof akka.actor.Status.Failure) {
             throw new AssertionError("Unexpected failure response", ((akka.actor.Status.Failure)resp).cause());
         }
 
@@ -579,28 +795,26 @@ public class DistributedDataStoreRemotingIntegrationTest {
         // Send another tx without immediate commit.
 
         modification = dataTree.takeSnapshot().newModification();
-        MapEntryNode car2 = CarsModel.newCarEntry("sportage", BigInteger.valueOf(30000));
+        MapEntryNode car2 = CarsModel.newCarEntry("sportage", Uint64.valueOf(30000));
         new WriteModification(CarsModel.newCarPath("sportage"), car2).apply(modification);
         modification.ready();
 
-        readyLocal = new ReadyLocalTransaction("tx-2" , modification, false);
+        readyLocal = new ReadyLocalTransaction(tx2 , modification, false, Optional.empty());
 
         carsFollowerShard.get().tell(readyLocal, followerTestKit.getRef());
         resp = followerTestKit.expectMsgClass(Object.class);
-        if(resp instanceof akka.actor.Status.Failure) {
+        if (resp instanceof akka.actor.Status.Failure) {
             throw new AssertionError("Unexpected failure response", ((akka.actor.Status.Failure)resp).cause());
         }
 
         assertEquals("Response type", ReadyTransactionReply.class, resp.getClass());
 
-        ActorSelection txActor = leaderDistributedDataStore.getActorContext().actorSelection(
+        final ActorSelection txActor = leaderDistributedDataStore.getActorUtils().actorSelection(
                 ((ReadyTransactionReply)resp).getCohortPath());
 
-        Supplier<Short> versionSupplier = Mockito.mock(Supplier.class);
-        Mockito.doReturn(DataStoreVersions.CURRENT_VERSION).when(versionSupplier).get();
-        ThreePhaseCommitCohortProxy cohort = new ThreePhaseCommitCohortProxy(
-                leaderDistributedDataStore.getActorContext(), Arrays.asList(
-                        new ThreePhaseCommitCohortProxy.CohortInfo(Futures.successful(txActor), versionSupplier)), "tx-2");
+        ThreePhaseCommitCohortProxy cohort = new ThreePhaseCommitCohortProxy(leaderDistributedDataStore.getActorUtils(),
+            List.of(new ThreePhaseCommitCohortProxy.CohortInfo(Futures.successful(txActor),
+                () -> DataStoreVersions.CURRENT_VERSION)), tx2);
         cohort.canCommit().get(5, TimeUnit.SECONDS);
         cohort.preCommit().get(5, TimeUnit.SECONDS);
         cohort.commit().get(5, TimeUnit.SECONDS);
@@ -612,13 +826,14 @@ public class DistributedDataStoreRemotingIntegrationTest {
     @Test
     public void testForwardedReadyTransactionForwardedToLeader() throws Exception {
         initDatastoresWithCars("testForwardedReadyTransactionForwardedToLeader");
-        followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorContext(), "cars");
+        followerTestKit.waitUntilLeader(followerDistributedDataStore.getActorUtils(), "cars");
 
-        Optional<ActorRef> carsFollowerShard = followerDistributedDataStore.getActorContext().findLocalShard("cars");
-        assertEquals("Cars follower shard found", true, carsFollowerShard.isPresent());
+        final Optional<ActorRef> carsFollowerShard =
+                followerDistributedDataStore.getActorUtils().findLocalShard("cars");
+        assertTrue("Cars follower shard found", carsFollowerShard.isPresent());
 
         carsFollowerShard.get().tell(GetShardDataTree.INSTANCE, followerTestKit.getRef());
-        DataTree dataTree = followerTestKit.expectMsgClass(DataTree.class);
+        final DataTree dataTree = followerTestKit.expectMsgClass(DataTree.class);
 
         // Send a tx with immediate commit.
 
@@ -626,16 +841,16 @@ public class DistributedDataStoreRemotingIntegrationTest {
         new WriteModification(CarsModel.BASE_PATH, CarsModel.emptyContainer()).apply(modification);
         new MergeModification(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode()).apply(modification);
 
-        MapEntryNode car1 = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
+        final MapEntryNode car1 = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
         new WriteModification(CarsModel.newCarPath("optima"), car1).apply(modification);
 
-        ForwardedReadyTransaction forwardedReady = new ForwardedReadyTransaction("tx-1",
-                DataStoreVersions.CURRENT_VERSION, new ReadWriteShardDataTreeTransaction(
-                        Mockito.mock(ShardDataTreeTransactionParent.class), "tx-1", modification), true);
+        ForwardedReadyTransaction forwardedReady = new ForwardedReadyTransaction(tx1, DataStoreVersions.CURRENT_VERSION,
+            new ReadWriteShardDataTreeTransaction(mock(ShardDataTreeTransactionParent.class), tx1, modification),
+            true, Optional.empty());
 
         carsFollowerShard.get().tell(forwardedReady, followerTestKit.getRef());
         Object resp = followerTestKit.expectMsgClass(Object.class);
-        if(resp instanceof akka.actor.Status.Failure) {
+        if (resp instanceof akka.actor.Status.Failure) {
             throw new AssertionError("Unexpected failure response", ((akka.actor.Status.Failure)resp).cause());
         }
 
@@ -646,29 +861,28 @@ public class DistributedDataStoreRemotingIntegrationTest {
         // Send another tx without immediate commit.
 
         modification = dataTree.takeSnapshot().newModification();
-        MapEntryNode car2 = CarsModel.newCarEntry("sportage", BigInteger.valueOf(30000));
+        MapEntryNode car2 = CarsModel.newCarEntry("sportage", Uint64.valueOf(30000));
         new WriteModification(CarsModel.newCarPath("sportage"), car2).apply(modification);
 
-        forwardedReady = new ForwardedReadyTransaction("tx-2",
-                DataStoreVersions.CURRENT_VERSION, new ReadWriteShardDataTreeTransaction(
-                        Mockito.mock(ShardDataTreeTransactionParent.class), "tx-2", modification), false);
+        forwardedReady = new ForwardedReadyTransaction(tx2, DataStoreVersions.CURRENT_VERSION,
+            new ReadWriteShardDataTreeTransaction(mock(ShardDataTreeTransactionParent.class), tx2, modification),
+            false, Optional.empty());
 
         carsFollowerShard.get().tell(forwardedReady, followerTestKit.getRef());
         resp = followerTestKit.expectMsgClass(Object.class);
-        if(resp instanceof akka.actor.Status.Failure) {
+        if (resp instanceof akka.actor.Status.Failure) {
             throw new AssertionError("Unexpected failure response", ((akka.actor.Status.Failure)resp).cause());
         }
 
         assertEquals("Response type", ReadyTransactionReply.class, resp.getClass());
 
-        ActorSelection txActor = leaderDistributedDataStore.getActorContext().actorSelection(
+        ActorSelection txActor = leaderDistributedDataStore.getActorUtils().actorSelection(
                 ((ReadyTransactionReply)resp).getCohortPath());
 
-        Supplier<Short> versionSupplier = Mockito.mock(Supplier.class);
-        Mockito.doReturn(DataStoreVersions.CURRENT_VERSION).when(versionSupplier).get();
-        ThreePhaseCommitCohortProxy cohort = new ThreePhaseCommitCohortProxy(
-                leaderDistributedDataStore.getActorContext(), Arrays.asList(
-                        new ThreePhaseCommitCohortProxy.CohortInfo(Futures.successful(txActor), versionSupplier)), "tx-2");
+        final ThreePhaseCommitCohortProxy cohort = new ThreePhaseCommitCohortProxy(
+            leaderDistributedDataStore.getActorUtils(), List.of(
+                new ThreePhaseCommitCohortProxy.CohortInfo(Futures.successful(txActor),
+                    () -> DataStoreVersions.CURRENT_VERSION)), tx2);
         cohort.canCommit().get(5, TimeUnit.SECONDS);
         cohort.preCommit().get(5, TimeUnit.SECONDS);
         cohort.commit().get(5, TimeUnit.SECONDS);
@@ -684,96 +898,98 @@ public class DistributedDataStoreRemotingIntegrationTest {
 
         // Do an initial write to get the primary shard info cached.
 
-        DOMStoreWriteTransaction initialWriteTx = followerDistributedDataStore.newWriteOnlyTransaction();
+        final DOMStoreWriteTransaction initialWriteTx = followerDistributedDataStore.newWriteOnlyTransaction();
         initialWriteTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
         initialWriteTx.write(PeopleModel.BASE_PATH, PeopleModel.emptyContainer());
         followerTestKit.doCommit(initialWriteTx.ready());
 
         // Wait for the commit to be replicated to the follower.
 
-        MemberNode.verifyRaftState(followerDistributedDataStore, "cars", new RaftStateVerifier() {
-            @Override
-            public void verify(OnDemandRaftState raftState) {
-                assertEquals("getLastApplied", 0, raftState.getLastApplied());
-            }
-        });
+        MemberNode.verifyRaftState(followerDistributedDataStore, "cars",
+            raftState -> assertEquals("getLastApplied", 1, raftState.getLastApplied()));
+
+        MemberNode.verifyRaftState(followerDistributedDataStore, "people",
+            raftState -> assertEquals("getLastApplied", 1, raftState.getLastApplied()));
 
         // Prepare, ready and canCommit a WO tx that writes to 2 shards. This will become the current tx in
         // the leader shard.
 
-        DOMStoreWriteTransaction writeTx1 = followerDistributedDataStore.newWriteOnlyTransaction();
+        final DOMStoreWriteTransaction writeTx1 = followerDistributedDataStore.newWriteOnlyTransaction();
         writeTx1.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
         writeTx1.write(PeopleModel.BASE_PATH, PeopleModel.emptyContainer());
-        DOMStoreThreePhaseCommitCohort writeTx1Cohort = writeTx1.ready();
-        ListenableFuture<Boolean> writeTx1CanCommit = writeTx1Cohort.canCommit();
+        final DOMStoreThreePhaseCommitCohort writeTx1Cohort = writeTx1.ready();
+        final ListenableFuture<Boolean> writeTx1CanCommit = writeTx1Cohort.canCommit();
         writeTx1CanCommit.get(5, TimeUnit.SECONDS);
 
         // Prepare and ready another WO tx that writes to 2 shards but don't canCommit yet. This will be queued
         // in the leader shard.
 
-        DOMStoreWriteTransaction writeTx2 = followerDistributedDataStore.newWriteOnlyTransaction();
-        LinkedList<MapEntryNode> cars = new LinkedList<>();
+        final DOMStoreWriteTransaction writeTx2 = followerDistributedDataStore.newWriteOnlyTransaction();
+        final LinkedList<MapEntryNode> cars = new LinkedList<>();
         int carIndex = 1;
-        cars.add(CarsModel.newCarEntry("car" + carIndex, BigInteger.valueOf(carIndex)));
+        cars.add(CarsModel.newCarEntry("car" + carIndex, Uint64.valueOf(carIndex)));
         writeTx2.write(CarsModel.newCarPath("car" + carIndex), cars.getLast());
         carIndex++;
-        NormalizedNode<?, ?> people = PeopleModel.newPersonMapNode();
+        NormalizedNode people = ImmutableNodes.mapNodeBuilder(PeopleModel.PERSON_QNAME)
+                .withChild(PeopleModel.newPersonEntry("Dude")).build();
         writeTx2.write(PeopleModel.PERSON_LIST_PATH, people);
-        DOMStoreThreePhaseCommitCohort writeTx2Cohort = writeTx2.ready();
+        final DOMStoreThreePhaseCommitCohort writeTx2Cohort = writeTx2.ready();
 
         // Prepare another WO that writes to a single shard and thus will be directly committed on ready. This
         // tx writes 5 cars so 2 BatchedModidifications messages will be sent initially and cached in the
         // leader shard (with shardBatchedModificationCount set to 2). The 3rd BatchedModidifications will be
         // sent on ready.
 
-        DOMStoreWriteTransaction writeTx3 = followerDistributedDataStore.newWriteOnlyTransaction();
-        for(int i = 1; i <= 5; i++, carIndex++) {
-            cars.add(CarsModel.newCarEntry("car" + carIndex, BigInteger.valueOf(carIndex)));
+        final DOMStoreWriteTransaction writeTx3 = followerDistributedDataStore.newWriteOnlyTransaction();
+        for (int i = 1; i <= 5; i++, carIndex++) {
+            cars.add(CarsModel.newCarEntry("car" + carIndex, Uint64.valueOf(carIndex)));
             writeTx3.write(CarsModel.newCarPath("car" + carIndex), cars.getLast());
         }
 
         // Prepare another WO that writes to a single shard. This will send a single BatchedModidifications
         // message on ready.
 
-        DOMStoreWriteTransaction writeTx4 = followerDistributedDataStore.newWriteOnlyTransaction();
-        cars.add(CarsModel.newCarEntry("car" + carIndex, BigInteger.valueOf(carIndex)));
+        final DOMStoreWriteTransaction writeTx4 = followerDistributedDataStore.newWriteOnlyTransaction();
+        cars.add(CarsModel.newCarEntry("car" + carIndex, Uint64.valueOf(carIndex)));
         writeTx4.write(CarsModel.newCarPath("car" + carIndex), cars.getLast());
         carIndex++;
 
         // Prepare a RW tx that will create a tx actor and send a ForwardedReadyTransaciton message to the
         // leader shard on ready.
 
-        DOMStoreReadWriteTransaction readWriteTx = followerDistributedDataStore.newReadWriteTransaction();
-        cars.add(CarsModel.newCarEntry("car" + carIndex, BigInteger.valueOf(carIndex)));
+        final DOMStoreReadWriteTransaction readWriteTx = followerDistributedDataStore.newReadWriteTransaction();
+        cars.add(CarsModel.newCarEntry("car" + carIndex, Uint64.valueOf(carIndex)));
         readWriteTx.write(CarsModel.newCarPath("car" + carIndex), cars.getLast());
 
-        IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars", new ShardStatsVerifier() {
-            @Override
-            public void verify(ShardStats stats) {
-                assertEquals("getReadWriteTransactionCount", 1, stats.getReadWriteTransactionCount());
-            }
-        });
+        // FIXME: CONTROLLER-2017: ClientBackedDataStore reports only 4 transactions
+        assumeTrue(DistributedDataStore.class.isAssignableFrom(testParameter));
+        IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars",
+            stats -> assertEquals("getReadWriteTransactionCount", 5, stats.getReadWriteTransactionCount()));
 
         // Disable elections on the leader so it switches to follower.
 
-        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder.
-                customRaftPolicyImplementation(DisableElectionsRaftPolicy.class.getName()).
-                shardElectionTimeoutFactor(10));
+        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder
+                .customRaftPolicyImplementation(DisableElectionsRaftPolicy.class.getName())
+                .shardElectionTimeoutFactor(10));
 
-        leaderTestKit.waitUntilNoLeader(leaderDistributedDataStore.getActorContext(), "cars");
+        leaderTestKit.waitUntilNoLeader(leaderDistributedDataStore.getActorUtils(), "cars");
 
         // Submit all tx's - the messages should get queued for retry.
 
-        ListenableFuture<Boolean> writeTx2CanCommit = writeTx2Cohort.canCommit();
-        DOMStoreThreePhaseCommitCohort writeTx3Cohort = writeTx3.ready();
-        DOMStoreThreePhaseCommitCohort writeTx4Cohort = writeTx4.ready();
-        DOMStoreThreePhaseCommitCohort rwTxCohort = readWriteTx.ready();
+        final ListenableFuture<Boolean> writeTx2CanCommit = writeTx2Cohort.canCommit();
+        final DOMStoreThreePhaseCommitCohort writeTx3Cohort = writeTx3.ready();
+        final DOMStoreThreePhaseCommitCohort writeTx4Cohort = writeTx4.ready();
+        final DOMStoreThreePhaseCommitCohort rwTxCohort = readWriteTx.ready();
 
         // Enable elections on the other follower so it becomes the leader, at which point the
         // tx's should get forwarded from the previous leader to the new leader to complete the commits.
 
-        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder.
-                customRaftPolicyImplementation(null).shardElectionTimeoutFactor(1));
+        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder
+                .customRaftPolicyImplementation(null).shardElectionTimeoutFactor(1));
+        IntegrationTestKit.findLocalShard(followerDistributedDataStore.getActorUtils(), "cars")
+                .tell(TimeoutNow.INSTANCE, ActorRef.noSender());
+        IntegrationTestKit.findLocalShard(followerDistributedDataStore.getActorUtils(), "people")
+                .tell(TimeoutNow.INSTANCE, ActorRef.noSender());
 
         followerTestKit.doCommit(writeTx1CanCommit, writeTx1Cohort);
         followerTestKit.doCommit(writeTx2CanCommit, writeTx2Cohort);
@@ -790,207 +1006,491 @@ public class DistributedDataStoreRemotingIntegrationTest {
     public void testLeadershipTransferOnShutdown() throws Exception {
         leaderDatastoreContextBuilder.shardBatchedModificationCount(1);
         followerDatastoreContextBuilder.shardElectionTimeoutFactor(10).customRaftPolicyImplementation(null);
-        String testName = "testLeadershipTransferOnShutdown";
+        final String testName = "testLeadershipTransferOnShutdown";
         initDatastores(testName, MODULE_SHARDS_CARS_PEOPLE_1_2_3, CARS_AND_PEOPLE);
 
-        IntegrationTestKit follower2TestKit = new IntegrationTestKit(follower2System, followerDatastoreContextBuilder);
-        DistributedDataStore follower2DistributedDataStore = follower2TestKit.setupDistributedDataStore(testName,
-                MODULE_SHARDS_CARS_PEOPLE_1_2_3, false);
+        final IntegrationTestKit follower2TestKit = new IntegrationTestKit(follower2System,
+                DatastoreContext.newBuilderFrom(followerDatastoreContextBuilder.build()).operationTimeoutInMillis(500),
+                commitTimeout);
+        try (AbstractDataStore follower2DistributedDataStore = follower2TestKit.setupAbstractDataStore(
+                testParameter, testName, MODULE_SHARDS_CARS_PEOPLE_1_2_3, false)) {
 
-        // Create and submit a couple tx's so they're pending.
+            followerTestKit.waitForMembersUp("member-3");
+            follower2TestKit.waitForMembersUp("member-1", "member-2");
 
-        DOMStoreWriteTransaction writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
-        writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
-        writeTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
-        writeTx.write(PeopleModel.BASE_PATH, PeopleModel.emptyContainer());
-        DOMStoreThreePhaseCommitCohort cohort1 = writeTx.ready();
+            // Create and submit a couple tx's so they're pending.
 
-        IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars", new ShardStatsVerifier() {
-            @Override
-            public void verify(ShardStats stats) {
-                assertEquals("getTxCohortCacheSize", 1, stats.getTxCohortCacheSize());
+            DOMStoreWriteTransaction writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
+            writeTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+            writeTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
+            writeTx.write(PeopleModel.BASE_PATH, PeopleModel.emptyContainer());
+            final DOMStoreThreePhaseCommitCohort cohort1 = writeTx.ready();
+
+            final var usesCohorts = DistributedDataStore.class.isAssignableFrom(testParameter);
+            if (usesCohorts) {
+                IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars",
+                    stats -> assertEquals("getTxCohortCacheSize", 1, stats.getTxCohortCacheSize()));
             }
-        });
 
-        writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
-        MapEntryNode car = CarsModel.newCarEntry("optima", BigInteger.valueOf(20000));
-        writeTx.write(CarsModel.newCarPath("optima"), car);
-        DOMStoreThreePhaseCommitCohort cohort2 = writeTx.ready();
-
-        IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars", new ShardStatsVerifier() {
-            @Override
-            public void verify(ShardStats stats) {
-                assertEquals("getTxCohortCacheSize", 2, stats.getTxCohortCacheSize());
+            writeTx = followerDistributedDataStore.newWriteOnlyTransaction();
+            final MapEntryNode car = CarsModel.newCarEntry("optima", Uint64.valueOf(20000));
+            writeTx.write(CarsModel.newCarPath("optima"), car);
+            final DOMStoreThreePhaseCommitCohort cohort2 = writeTx.ready();
+
+            if (usesCohorts) {
+                IntegrationTestKit.verifyShardStats(leaderDistributedDataStore, "cars",
+                    stats -> assertEquals("getTxCohortCacheSize", 2, stats.getTxCohortCacheSize()));
             }
-        });
 
-        // Gracefully stop the leader via a Shutdown message.
+            // Gracefully stop the leader via a Shutdown message.
 
-        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder.
-                shardElectionTimeoutFactor(100));
+            sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder
+                .shardElectionTimeoutFactor(100));
 
-        FiniteDuration duration = FiniteDuration.create(5, TimeUnit.SECONDS);
-        Future<ActorRef> future = leaderDistributedDataStore.getActorContext().findLocalShardAsync("cars");
-        ActorRef leaderActor = Await.result(future, duration);
+            final FiniteDuration duration = FiniteDuration.create(5, TimeUnit.SECONDS);
+            final Future<ActorRef> future = leaderDistributedDataStore.getActorUtils().findLocalShardAsync("cars");
+            final ActorRef leaderActor = Await.result(future, duration);
 
-        Future<Boolean> stopFuture = Patterns.gracefulStop(leaderActor, duration, Shutdown.INSTANCE);
+            final Future<Boolean> stopFuture = Patterns.gracefulStop(leaderActor, duration, Shutdown.INSTANCE);
 
-        // Commit the 2 transactions. They should finish and succeed.
+            // Commit the 2 transactions. They should finish and succeed.
 
-        followerTestKit.doCommit(cohort1);
-        followerTestKit.doCommit(cohort2);
+            followerTestKit.doCommit(cohort1);
+            followerTestKit.doCommit(cohort2);
 
-        // Wait for the leader actor stopped.
+            // Wait for the leader actor stopped.
 
-        Boolean stopped = Await.result(stopFuture, duration);
-        assertEquals("Stopped", Boolean.TRUE, stopped);
+            final Boolean stopped = Await.result(stopFuture, duration);
+            assertEquals("Stopped", Boolean.TRUE, stopped);
 
-        // Verify leadership was transferred by reading the committed data from the other nodes.
+            // Verify leadership was transferred by reading the committed data from the other nodes.
 
-        verifyCars(followerDistributedDataStore.newReadOnlyTransaction(), car);
-        verifyCars(follower2DistributedDataStore.newReadOnlyTransaction(), car);
+            verifyCars(followerDistributedDataStore.newReadOnlyTransaction(), car);
+            verifyCars(follower2DistributedDataStore.newReadOnlyTransaction(), car);
+        }
     }
 
     @Test
-    public void testTransactionWithIsolatedLeader() throws Throwable {
-        leaderDatastoreContextBuilder.shardIsolatedLeaderCheckIntervalInMillis(200);
-        String testName = "testTransactionWithIsolatedLeader";
+    public void testTransactionWithIsolatedLeader() throws Exception {
+        // FIXME: CONTROLLER-2018: remove when test passes also for ClientBackedDataStore
+        assumeTrue(DistributedDataStore.class.isAssignableFrom(testParameter));
+
+        // Set the isolated leader check interval high so we can control the switch to IsolatedLeader.
+        leaderDatastoreContextBuilder.shardIsolatedLeaderCheckIntervalInMillis(10000000);
+        final String testName = "testTransactionWithIsolatedLeader";
         initDatastoresWithCars(testName);
 
-        DOMStoreWriteTransaction failWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
-        failWriteTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+        // Tx that is submitted after the follower is stopped but before the leader transitions to IsolatedLeader.
+        final DOMStoreWriteTransaction preIsolatedLeaderWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
+        preIsolatedLeaderWriteTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+
+        // Tx that is submitted after the leader transitions to IsolatedLeader.
+        final DOMStoreWriteTransaction noShardLeaderWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
+        noShardLeaderWriteTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
-        DOMStoreWriteTransaction successWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
+        // Tx that is submitted after the follower is reinstated.
+        final DOMStoreWriteTransaction successWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
         successWriteTx.merge(CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
-        followerTestKit.watch(followerDistributedDataStore.getActorContext().getShardManager());
+        // Stop the follower
+        followerTestKit.watch(followerDistributedDataStore.getActorUtils().getShardManager());
         followerDistributedDataStore.close();
-        followerTestKit.expectTerminated(followerDistributedDataStore.getActorContext().getShardManager());
+        followerTestKit.expectTerminated(followerDistributedDataStore.getActorUtils().getShardManager());
 
-        MemberNode.verifyRaftState(leaderDistributedDataStore, "cars", new RaftStateVerifier() {
-            @Override
-            public void verify(OnDemandRaftState raftState) {
-                assertEquals("getRaftState", "IsolatedLeader", raftState.getRaftState());
-            }
-        });
+        // Submit the preIsolatedLeaderWriteTx so it's pending
+        final DOMStoreThreePhaseCommitCohort preIsolatedLeaderTxCohort = preIsolatedLeaderWriteTx.ready();
 
-        try {
-            leaderTestKit.doCommit(failWriteTx.ready());
-            fail("Expected NoShardLeaderException");
-        } catch (ExecutionException e) {
-            assertEquals("getCause", NoShardLeaderException.class, e.getCause().getClass());
-        }
+        // Change the isolated leader check interval low so it changes to IsolatedLeader.
+        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder
+                .shardIsolatedLeaderCheckIntervalInMillis(200));
+
+        MemberNode.verifyRaftState(leaderDistributedDataStore, "cars",
+            raftState -> assertEquals("getRaftState", "IsolatedLeader", raftState.getRaftState()));
 
-        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder.
-                shardElectionTimeoutFactor(100));
+        final var ex = assertThrows(ExecutionException.class,
+            () -> leaderTestKit.doCommit(noShardLeaderWriteTx.ready()));
+        assertEquals(NoShardLeaderException.class, Throwables.getRootCause(ex).getClass());
 
-        DOMStoreThreePhaseCommitCohort writeTxCohort = successWriteTx.ready();
+        sendDatastoreContextUpdate(leaderDistributedDataStore, leaderDatastoreContextBuilder
+                .shardElectionTimeoutFactor(100));
 
-        followerDistributedDataStore = followerTestKit.setupDistributedDataStore(testName,
-                MODULE_SHARDS_CARS_ONLY_1_2, false, CARS);
+        final DOMStoreThreePhaseCommitCohort successTxCohort = successWriteTx.ready();
 
-        leaderTestKit.doCommit(writeTxCohort);
+        followerDistributedDataStore = followerTestKit.setupAbstractDataStore(
+                testParameter, testName, MODULE_SHARDS_CARS_ONLY_1_2, false, CARS);
+
+        leaderTestKit.doCommit(preIsolatedLeaderTxCohort);
+        leaderTestKit.doCommit(successTxCohort);
     }
 
-    @Test(expected=AskTimeoutException.class)
-    public void testTransactionWithShardLeaderNotResponding() throws Throwable {
+    @Test
+    public void testTransactionWithShardLeaderNotResponding() throws Exception {
+        followerDatastoreContextBuilder.frontendRequestTimeoutInSeconds(2);
+        followerDatastoreContextBuilder.shardElectionTimeoutFactor(50);
         initDatastoresWithCars("testTransactionWithShardLeaderNotResponding");
 
         // Do an initial read to get the primary shard info cached.
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
-        readTx.read(CarsModel.BASE_PATH).checkedGet(5, TimeUnit.SECONDS);
+        final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+        readTx.read(CarsModel.BASE_PATH).get(5, TimeUnit.SECONDS);
 
         // Shutdown the leader and try to create a new tx.
 
-        JavaTestKit.shutdownActorSystem(leaderSystem, null, true);
+        TestKit.shutdownActorSystem(leaderSystem, true);
 
         followerDatastoreContextBuilder.operationTimeoutInMillis(50).shardElectionTimeoutFactor(1);
         sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder);
 
-        DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
 
         rwTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
-        try {
-            followerTestKit.doCommit(rwTx.ready());
-        } catch (ExecutionException e) {
-            assertTrue("Expected ShardLeaderNotRespondingException cause. Actual: " + e.getCause(),
-                    e.getCause() instanceof ShardLeaderNotRespondingException);
-            assertNotNull("Expected a nested cause", e.getCause().getCause());
-            throw e.getCause().getCause();
+        final var ex = assertThrows(ExecutionException.class, () -> followerTestKit.doCommit(rwTx.ready()));
+        final String msg = "Unexpected exception: " + Throwables.getStackTraceAsString(ex.getCause());
+        if (DistributedDataStore.class.isAssignableFrom(testParameter)) {
+            assertTrue(msg, Throwables.getRootCause(ex) instanceof NoShardLeaderException
+                || ex.getCause() instanceof ShardLeaderNotRespondingException);
+        } else {
+            assertThat(msg, Throwables.getRootCause(ex), instanceOf(RequestTimeoutException.class));
         }
     }
 
-    @Test(expected=NoShardLeaderException.class)
-    public void testTransactionWithCreateTxFailureDueToNoLeader() throws Throwable {
+    @Test
+    public void testTransactionWithCreateTxFailureDueToNoLeader() throws Exception {
+        followerDatastoreContextBuilder.frontendRequestTimeoutInSeconds(2);
         initDatastoresWithCars("testTransactionWithCreateTxFailureDueToNoLeader");
 
         // Do an initial read to get the primary shard info cached.
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
-        readTx.read(CarsModel.BASE_PATH).checkedGet(5, TimeUnit.SECONDS);
+        final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+        readTx.read(CarsModel.BASE_PATH).get(5, TimeUnit.SECONDS);
 
         // Shutdown the leader and try to create a new tx.
 
-        JavaTestKit.shutdownActorSystem(leaderSystem, null, true);
+        TestKit.shutdownActorSystem(leaderSystem, true);
+
+        Cluster.get(followerSystem).leave(MEMBER_1_ADDRESS);
 
         Uninterruptibles.sleepUninterruptibly(100, TimeUnit.MILLISECONDS);
 
-        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder.
-                operationTimeoutInMillis(10).shardElectionTimeoutFactor(1).customRaftPolicyImplementation(null));
+        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder
+                .operationTimeoutInMillis(10).shardElectionTimeoutFactor(1).customRaftPolicyImplementation(null));
 
-        DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+        final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
 
         rwTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
 
-        try {
-            followerTestKit.doCommit(rwTx.ready());
-        } catch (ExecutionException e) {
-            throw e.getCause();
+        final var ex = assertThrows(ExecutionException.class, () -> followerTestKit.doCommit(rwTx.ready()));
+        final String msg = "Unexpected exception: " + Throwables.getStackTraceAsString(ex.getCause());
+        if (DistributedDataStore.class.isAssignableFrom(testParameter)) {
+            assertThat(msg, Throwables.getRootCause(ex), instanceOf(NoShardLeaderException.class));
+        } else {
+            assertThat(msg, Throwables.getRootCause(ex), instanceOf(RequestTimeoutException.class));
         }
     }
 
     @Test
     public void testTransactionRetryWithInitialAskTimeoutExOnCreateTx() throws Exception {
+        followerDatastoreContextBuilder.backendAlivenessTimerIntervalInSeconds(2);
         String testName = "testTransactionRetryWithInitialAskTimeoutExOnCreateTx";
-        initDatastores(testName, MODULE_SHARDS_CARS_PEOPLE_1_2_3, CARS);
+        initDatastores(testName, MODULE_SHARDS_CARS_1_2_3, CARS);
 
-        DatastoreContext.Builder follower2DatastoreContextBuilder = DatastoreContext.newBuilder().
-                shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(5);
-        IntegrationTestKit follower2TestKit = new IntegrationTestKit(follower2System, follower2DatastoreContextBuilder);
-        follower2TestKit.setupDistributedDataStore(testName, MODULE_SHARDS_CARS_PEOPLE_1_2_3, false, CARS);
+        final DatastoreContext.Builder follower2DatastoreContextBuilder = DatastoreContext.newBuilder()
+                .shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(10);
+        final IntegrationTestKit follower2TestKit = new IntegrationTestKit(
+                follower2System, follower2DatastoreContextBuilder, commitTimeout);
 
-        // Do an initial read to get the primary shard info cached.
+        try (AbstractDataStore ds =
+                follower2TestKit.setupAbstractDataStore(
+                        testParameter, testName, MODULE_SHARDS_CARS_1_2_3, false, CARS)) {
 
-        DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
-        readTx.read(CarsModel.BASE_PATH).checkedGet(5, TimeUnit.SECONDS);
+            followerTestKit.waitForMembersUp("member-1", "member-3");
+            follower2TestKit.waitForMembersUp("member-1", "member-2");
 
-        // Shutdown the leader and try to create a new tx.
+            // Do an initial read to get the primary shard info cached.
 
-        JavaTestKit.shutdownActorSystem(leaderSystem, null, true);
+            final DOMStoreReadTransaction readTx = followerDistributedDataStore.newReadOnlyTransaction();
+            readTx.read(CarsModel.BASE_PATH).get(5, TimeUnit.SECONDS);
 
-        sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder.
-                operationTimeoutInMillis(500).shardElectionTimeoutFactor(1).customRaftPolicyImplementation(null));
+            // Shutdown the leader and try to create a new tx.
 
-        DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+            TestKit.shutdownActorSystem(leaderSystem, true);
 
-        rwTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+            Cluster.get(followerSystem).leave(MEMBER_1_ADDRESS);
 
-        followerTestKit.doCommit(rwTx.ready());
+            sendDatastoreContextUpdate(followerDistributedDataStore, followerDatastoreContextBuilder
+                .operationTimeoutInMillis(500).shardElectionTimeoutFactor(5).customRaftPolicyImplementation(null));
+
+            final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+
+            rwTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+
+            followerTestKit.doCommit(rwTx.ready());
+        }
     }
 
-    private static void sendDatastoreContextUpdate(DistributedDataStore dataStore, final Builder builder) {
-        final Builder newBuilder = DatastoreContext.newBuilderFrom(builder.build());
-        DatastoreContextFactory mockContextFactory = Mockito.mock(DatastoreContextFactory.class);
-        Answer<DatastoreContext> answer = new Answer<DatastoreContext>() {
-            @Override
-            public DatastoreContext answer(InvocationOnMock invocation) {
-                return newBuilder.build();
+    @Test
+    public void testSemiReachableCandidateNotDroppingLeader() throws Exception {
+        final String testName = "testSemiReachableCandidateNotDroppingLeader";
+        initDatastores(testName, MODULE_SHARDS_CARS_1_2_3, CARS);
+
+        final DatastoreContext.Builder follower2DatastoreContextBuilder = DatastoreContext.newBuilder()
+                .shardHeartbeatIntervalInMillis(100).shardElectionTimeoutFactor(10);
+        final IntegrationTestKit follower2TestKit = new IntegrationTestKit(
+                follower2System, follower2DatastoreContextBuilder, commitTimeout);
+
+        final AbstractDataStore ds2 =
+                     follower2TestKit.setupAbstractDataStore(
+                             testParameter, testName, MODULE_SHARDS_CARS_1_2_3, false, CARS);
+
+        followerTestKit.waitForMembersUp("member-1", "member-3");
+        follower2TestKit.waitForMembersUp("member-1", "member-2");
+
+        // behavior is controlled by akka.coordinated-shutdown.run-by-actor-system-terminate configuration option
+        TestKit.shutdownActorSystem(follower2System, true);
+
+        ActorRef cars = leaderDistributedDataStore.getActorUtils().findLocalShard("cars").get();
+        final OnDemandRaftState initialState = (OnDemandRaftState) leaderDistributedDataStore.getActorUtils()
+                .executeOperation(cars, GetOnDemandRaftState.INSTANCE);
+
+        Cluster leaderCluster = Cluster.get(leaderSystem);
+        Cluster followerCluster = Cluster.get(followerSystem);
+        Cluster follower2Cluster = Cluster.get(follower2System);
+
+        Member follower2Member = follower2Cluster.readView().self();
+
+        await().atMost(10, TimeUnit.SECONDS)
+                .until(() -> containsUnreachable(leaderCluster, follower2Member));
+        await().atMost(10, TimeUnit.SECONDS)
+                .until(() -> containsUnreachable(followerCluster, follower2Member));
+
+        ActorRef followerCars = followerDistributedDataStore.getActorUtils().findLocalShard("cars").get();
+
+        // to simulate a follower not being able to receive messages, but still being able to send messages and becoming
+        // candidate, we can just send a couple of RequestVotes to both leader and follower.
+        cars.tell(new RequestVote(initialState.getCurrentTerm() + 1, "member-3-shard-cars", -1, -1), null);
+        followerCars.tell(new RequestVote(initialState.getCurrentTerm() + 1, "member-3-shard-cars", -1, -1), null);
+        cars.tell(new RequestVote(initialState.getCurrentTerm() + 3, "member-3-shard-cars", -1, -1), null);
+        followerCars.tell(new RequestVote(initialState.getCurrentTerm() + 3, "member-3-shard-cars", -1, -1), null);
+
+        OnDemandRaftState stateAfter = (OnDemandRaftState) leaderDistributedDataStore.getActorUtils()
+                .executeOperation(cars, GetOnDemandRaftState.INSTANCE);
+        OnDemandRaftState followerState = (OnDemandRaftState) followerDistributedDataStore.getActorUtils()
+                .executeOperation(cars, GetOnDemandRaftState.INSTANCE);
+
+        assertEquals(initialState.getCurrentTerm(), stateAfter.getCurrentTerm());
+        assertEquals(initialState.getCurrentTerm(), followerState.getCurrentTerm());
+
+        ds2.close();
+    }
+
+    private static Boolean containsUnreachable(final Cluster cluster, final Member member) {
+        // unreachableMembers() returns scala.collection.immutable.Set, but we are using scala.collection.Set to fix JDT
+        // see https://bugs.eclipse.org/bugs/show_bug.cgi?id=468276#c32
+        final Set<Member> members = cluster.readView().unreachableMembers();
+        return members.contains(member);
+    }
+
+    @Test
+    public void testInstallSnapshot() throws Exception {
+        final String testName = "testInstallSnapshot";
+        final String leaderCarShardName = "member-1-shard-cars-" + testName;
+        final String followerCarShardName = "member-2-shard-cars-" + testName;
+
+        // Setup a saved snapshot on the leader. The follower will startup with no data and the leader should
+        // install a snapshot to sync the follower.
+
+        DataTree tree = new InMemoryDataTreeFactory().create(DataTreeConfiguration.DEFAULT_CONFIGURATION,
+            SchemaContextHelper.full());
+
+        final ContainerNode carsNode = CarsModel.newCarsNode(
+                CarsModel.newCarsMapNode(CarsModel.newCarEntry("optima", Uint64.valueOf(20000))));
+        AbstractShardTest.writeToStore(tree, CarsModel.BASE_PATH, carsNode);
+
+        final NormalizedNode snapshotRoot = AbstractShardTest.readStore(tree, YangInstanceIdentifier.empty());
+        final Snapshot initialSnapshot = Snapshot.create(
+                new ShardSnapshotState(new MetadataShardDataTreeSnapshot(snapshotRoot)),
+                Collections.emptyList(), 5, 1, 5, 1, 1, null, null);
+        InMemorySnapshotStore.addSnapshot(leaderCarShardName, initialSnapshot);
+
+        InMemorySnapshotStore.addSnapshotSavedLatch(leaderCarShardName);
+        InMemorySnapshotStore.addSnapshotSavedLatch(followerCarShardName);
+
+        initDatastoresWithCars(testName);
+
+        assertEquals(Optional.of(carsNode), leaderDistributedDataStore.newReadOnlyTransaction().read(
+            CarsModel.BASE_PATH).get(5, TimeUnit.SECONDS));
+
+        verifySnapshot(InMemorySnapshotStore.waitForSavedSnapshot(leaderCarShardName, Snapshot.class),
+                initialSnapshot, snapshotRoot);
+
+        verifySnapshot(InMemorySnapshotStore.waitForSavedSnapshot(followerCarShardName, Snapshot.class),
+                initialSnapshot, snapshotRoot);
+    }
+
+    @Test
+    public void testReadWriteMessageSlicing() throws Exception {
+        // The slicing is only implemented for tell-based protocol
+        assumeTrue(ClientBackedDataStore.class.isAssignableFrom(testParameter));
+
+        leaderDatastoreContextBuilder.maximumMessageSliceSize(100);
+        followerDatastoreContextBuilder.maximumMessageSliceSize(100);
+        initDatastoresWithCars("testLargeReadReplySlicing");
+
+        final DOMStoreReadWriteTransaction rwTx = followerDistributedDataStore.newReadWriteTransaction();
+
+        final NormalizedNode carsNode = CarsModel.create();
+        rwTx.write(CarsModel.BASE_PATH, carsNode);
+
+        verifyNode(rwTx, CarsModel.BASE_PATH, carsNode);
+    }
+
+    @SuppressWarnings("IllegalCatch")
+    @Test
+    public void testRaftCallbackDuringLeadershipDrop() throws Exception {
+        final String testName = "testRaftCallbackDuringLeadershipDrop";
+        initDatastores(testName, MODULE_SHARDS_CARS_1_2_3, CARS);
+
+        final ExecutorService executor = Executors.newSingleThreadExecutor();
+
+        final IntegrationTestKit follower2TestKit = new IntegrationTestKit(follower2System,
+                DatastoreContext.newBuilderFrom(followerDatastoreContextBuilder.build()).operationTimeoutInMillis(500)
+                        .shardLeaderElectionTimeoutInSeconds(3600),
+                commitTimeout);
+
+        final DOMStoreWriteTransaction initialWriteTx = leaderDistributedDataStore.newWriteOnlyTransaction();
+        initialWriteTx.write(CarsModel.BASE_PATH, CarsModel.emptyContainer());
+        leaderTestKit.doCommit(initialWriteTx.ready());
+
+        try (AbstractDataStore follower2DistributedDataStore = follower2TestKit.setupAbstractDataStore(
+                testParameter, testName, MODULE_SHARDS_CARS_1_2_3, false)) {
+
+            final ActorRef member3Cars = ((LocalShardStore) follower2DistributedDataStore).getLocalShards()
+                    .getLocalShards().get("cars").getActor();
+            final ActorRef member2Cars = ((LocalShardStore)followerDistributedDataStore).getLocalShards()
+                    .getLocalShards().get("cars").getActor();
+            member2Cars.tell(new StartDropMessages(AppendEntries.class), null);
+            member3Cars.tell(new StartDropMessages(AppendEntries.class), null);
+
+            final DOMStoreWriteTransaction newTx = leaderDistributedDataStore.newWriteOnlyTransaction();
+            newTx.write(CarsModel.CAR_LIST_PATH, CarsModel.newCarMapNode());
+            final AtomicBoolean submitDone = new AtomicBoolean(false);
+            executor.submit(() -> {
+                try {
+                    leaderTestKit.doCommit(newTx.ready());
+                    submitDone.set(true);
+                } catch (Exception e) {
+                    throw new RuntimeException(e);
+                }
+            });
+            final ActorRef leaderCars = ((LocalShardStore) leaderDistributedDataStore).getLocalShards()
+                    .getLocalShards().get("cars").getActor();
+            await().atMost(10, TimeUnit.SECONDS)
+                    .until(() -> ((OnDemandRaftState) leaderDistributedDataStore.getActorUtils()
+                            .executeOperation(leaderCars, GetOnDemandRaftState.INSTANCE)).getLastIndex() >= 1);
+
+            final OnDemandRaftState raftState = (OnDemandRaftState)leaderDistributedDataStore.getActorUtils()
+                    .executeOperation(leaderCars, GetOnDemandRaftState.INSTANCE);
+
+            // Simulate a follower not receiving heartbeats but still being able to send messages ie RequestVote with
+            // new term(switching to candidate after election timeout)
+            leaderCars.tell(new RequestVote(raftState.getCurrentTerm() + 1,
+                    "member-3-shard-cars-testRaftCallbackDuringLeadershipDrop", -1,
+                            -1), member3Cars);
+
+            member2Cars.tell(new StopDropMessages(AppendEntries.class), null);
+            member3Cars.tell(new StopDropMessages(AppendEntries.class), null);
+
+            await("Is tx stuck in COMMIT_PENDING")
+                    .atMost(10, TimeUnit.SECONDS).untilAtomic(submitDone, equalTo(true));
+
+        }
+
+        executor.shutdownNow();
+    }
+
+    @Test
+    public void testSnapshotOnRootOverwrite() throws Exception {
+        initDatastores("testSnapshotOnRootOverwrite", "module-shards-default-cars-member1-and-2.conf",
+            new String[] {"cars", "default"},
+            leaderDatastoreContextBuilder.snapshotOnRootOverwrite(true),
+            followerDatastoreContextBuilder.snapshotOnRootOverwrite(true));
+
+        leaderTestKit.waitForMembersUp("member-2");
+        final ContainerNode rootNode = ImmutableContainerNodeBuilder.create()
+                .withNodeIdentifier(YangInstanceIdentifier.NodeIdentifier.create(SchemaContext.NAME))
+                .withChild(CarsModel.create())
+                .build();
+
+        leaderTestKit.testWriteTransaction(leaderDistributedDataStore, YangInstanceIdentifier.empty(), rootNode);
+
+        // FIXME: CONTROLLER-2020: ClientBackedDatastore does not have stable indexes/term,
+        //                         the snapshot index seems to fluctuate
+        assumeTrue(DistributedDataStore.class.isAssignableFrom(testParameter));
+        IntegrationTestKit.verifyShardState(leaderDistributedDataStore, "cars",
+            state -> assertEquals(1, state.getSnapshotIndex()));
+
+        IntegrationTestKit.verifyShardState(followerDistributedDataStore, "cars",
+            state -> assertEquals(1, state.getSnapshotIndex()));
+
+        verifySnapshot("member-1-shard-cars-testSnapshotOnRootOverwrite", 1);
+        verifySnapshot("member-2-shard-cars-testSnapshotOnRootOverwrite", 1);
+
+        for (int i = 0; i < 10; i++) {
+            leaderTestKit.testWriteTransaction(leaderDistributedDataStore, CarsModel.newCarPath("car " + i),
+                    CarsModel.newCarEntry("car " + i, Uint64.ONE));
+        }
+
+        // fake snapshot causes the snapshotIndex to move
+        IntegrationTestKit.verifyShardState(leaderDistributedDataStore, "cars",
+            state -> assertEquals(10, state.getSnapshotIndex()));
+        IntegrationTestKit.verifyShardState(followerDistributedDataStore, "cars",
+            state -> assertEquals(10, state.getSnapshotIndex()));
+
+        // however the real snapshot still has not changed and was taken at index 1
+        verifySnapshot("member-1-shard-cars-testSnapshotOnRootOverwrite", 1);
+        verifySnapshot("member-2-shard-cars-testSnapshotOnRootOverwrite", 1);
+
+        // root overwrite so expect a snapshot
+        leaderTestKit.testWriteTransaction(leaderDistributedDataStore, YangInstanceIdentifier.empty(), rootNode);
+
+        // this was a real snapshot so everything should be in it(1(DisableTrackingPayload) + 1 + 10 + 1)
+        IntegrationTestKit.verifyShardState(leaderDistributedDataStore, "cars",
+            state -> assertEquals(12, state.getSnapshotIndex()));
+        IntegrationTestKit.verifyShardState(followerDistributedDataStore, "cars",
+            state -> assertEquals(12, state.getSnapshotIndex()));
+
+        verifySnapshot("member-1-shard-cars-testSnapshotOnRootOverwrite", 12);
+        verifySnapshot("member-2-shard-cars-testSnapshotOnRootOverwrite", 12);
+    }
+
+    private static void verifySnapshot(final String persistenceId, final long lastAppliedIndex) {
+        await().atMost(5, TimeUnit.SECONDS).untilAsserted(() -> {
+                List<Snapshot> snap = InMemorySnapshotStore.getSnapshots(persistenceId, Snapshot.class);
+                assertEquals(1, snap.size());
+                assertEquals(lastAppliedIndex, snap.get(0).getLastAppliedIndex());
             }
-        };
-        Mockito.doAnswer(answer).when(mockContextFactory).getBaseDatastoreContext();
-        Mockito.doAnswer(answer).when(mockContextFactory).getShardDatastoreContext(Mockito.anyString());
+        );
+    }
+
+    private static void verifySnapshot(final Snapshot actual, final Snapshot expected,
+                                       final NormalizedNode expRoot) {
+        assertEquals("Snapshot getLastAppliedTerm", expected.getLastAppliedTerm(), actual.getLastAppliedTerm());
+        assertEquals("Snapshot getLastAppliedIndex", expected.getLastAppliedIndex(), actual.getLastAppliedIndex());
+        assertEquals("Snapshot getLastTerm", expected.getLastTerm(), actual.getLastTerm());
+        assertEquals("Snapshot getLastIndex", expected.getLastIndex(), actual.getLastIndex());
+        assertEquals("Snapshot state type", ShardSnapshotState.class, actual.getState().getClass());
+        MetadataShardDataTreeSnapshot shardSnapshot =
+                (MetadataShardDataTreeSnapshot) ((ShardSnapshotState)actual.getState()).getSnapshot();
+        assertEquals("Snapshot root node", expRoot, shardSnapshot.getRootNode().get());
+    }
+
+    private static void sendDatastoreContextUpdate(final AbstractDataStore dataStore, final Builder builder) {
+        final Builder newBuilder = DatastoreContext.newBuilderFrom(builder.build());
+        final DatastoreContextFactory mockContextFactory = mock(DatastoreContextFactory.class);
+        final Answer<DatastoreContext> answer = invocation -> newBuilder.build();
+        doAnswer(answer).when(mockContextFactory).getBaseDatastoreContext();
+        doAnswer(answer).when(mockContextFactory).getShardDatastoreContext(anyString());
         dataStore.onDatastoreContextUpdated(mockContextFactory);
     }
 }