Create transaction on the backend datastore only when neccessary
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / test / java / org / opendaylight / controller / cluster / datastore / ShardTest.java
index e04c1a5d185ffbb5bc81b4d035a07545c02ef3a7..22ce50b90dff49f0f960176741adeb214c913e9e 100644 (file)
@@ -8,6 +8,7 @@ import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
 import static org.opendaylight.controller.cluster.datastore.DataStoreVersions.CURRENT_VERSION;
 import akka.actor.ActorRef;
 import akka.actor.ActorSelection;
@@ -17,6 +18,7 @@ import akka.dispatch.Dispatchers;
 import akka.dispatch.OnComplete;
 import akka.japi.Creator;
 import akka.pattern.Patterns;
+import akka.persistence.SaveSnapshotSuccess;
 import akka.testkit.TestActorRef;
 import akka.util.Timeout;
 import com.google.common.base.Function;
@@ -87,7 +89,6 @@ import org.opendaylight.controller.md.cluster.datastore.model.TestModel;
 import org.opendaylight.controller.md.sal.common.api.data.AsyncDataBroker;
 import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
 import org.opendaylight.controller.md.sal.dom.store.impl.InMemoryDOMDataStore;
-import org.opendaylight.controller.md.sal.dom.store.impl.InMemoryDOMDataStoreFactory;
 import org.opendaylight.controller.protobuff.messages.cohort3pc.ThreePhaseCommitCohortMessages;
 import org.opendaylight.controller.protobuff.messages.transaction.ShardTransactionMessages.CreateTransactionReply;
 import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
@@ -98,7 +99,9 @@ import org.opendaylight.yangtools.yang.data.api.schema.ContainerNode;
 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
+import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
+import org.opendaylight.yangtools.yang.data.impl.schema.tree.InMemoryDataTreeFactory;
 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
 import scala.concurrent.Await;
 import scala.concurrent.Future;
@@ -336,8 +339,8 @@ public class ShardTest extends AbstractShardTest {
         TestActorRef<Shard> shard = TestActorRef.create(getSystem(), newShardProps(),
                 "testApplySnapshot");
 
-        InMemoryDOMDataStore store = new InMemoryDOMDataStore("OPER", MoreExecutors.sameThreadExecutor());
-        store.onGlobalContextUpdated(SCHEMA_CONTEXT);
+        DataTree store = InMemoryDataTreeFactory.getInstance().create();
+        store.setSchemaContext(SCHEMA_CONTEXT);
 
         writeToStore(store, TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME));
 
@@ -380,8 +383,8 @@ public class ShardTest extends AbstractShardTest {
 
         // Set up the InMemorySnapshotStore.
 
-        InMemoryDOMDataStore testStore = InMemoryDOMDataStoreFactory.create("Test", null, null);
-        testStore.onGlobalContextUpdated(SCHEMA_CONTEXT);
+        DataTree testStore = InMemoryDataTreeFactory.getInstance().create();
+        testStore.setSchemaContext(SCHEMA_CONTEXT);
 
         writeToStore(testStore, TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME));
 
@@ -436,42 +439,42 @@ public class ShardTest extends AbstractShardTest {
 
             waitUntilLeader(shard);
 
-            final String transactionID1 = "tx1";
-            final String transactionID2 = "tx2";
-            final String transactionID3 = "tx3";
+         // Setup 3 simulated transactions with mock cohorts backed by real cohorts.
 
-            final AtomicReference<DOMStoreThreePhaseCommitCohort> mockCohort1 = new AtomicReference<>();
-            final AtomicReference<DOMStoreThreePhaseCommitCohort> mockCohort2 = new AtomicReference<>();
-            final AtomicReference<DOMStoreThreePhaseCommitCohort> mockCohort3 = new AtomicReference<>();
-            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
-                @Override
-                public DOMStoreThreePhaseCommitCohort decorate(String transactionID, DOMStoreThreePhaseCommitCohort actual) {
-                    if(transactionID.equals(transactionID1)) {
-                        mockCohort1.set(createDelegatingMockCohort("cohort1", actual));
-                        return mockCohort1.get();
-                    } else if(transactionID.equals(transactionID2)) {
-                        mockCohort2.set(createDelegatingMockCohort("cohort2", actual));
-                        return mockCohort2.get();
-                    } else {
-                        mockCohort3.set(createDelegatingMockCohort("cohort3", actual));
-                        return mockCohort3.get();
-                    }
-                }
-            };
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
 
-            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = setupMockWriteTransaction("cohort1", dataStore,
+                    TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME), modification1);
+
+            String transactionID2 = "tx2";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort2 = setupMockWriteTransaction("cohort2", dataStore,
+                    TestModel.OUTER_LIST_PATH,
+                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(),
+                    modification2);
+
+            String transactionID3 = "tx3";
+            MutableCompositeModification modification3 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort3 = setupMockWriteTransaction("cohort3", dataStore,
+                    YangInstanceIdentifier.builder(TestModel.OUTER_LIST_PATH)
+                        .nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
+                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1),
+                    modification3);
 
             long timeoutSec = 5;
             final FiniteDuration duration = FiniteDuration.create(timeoutSec, TimeUnit.SECONDS);
             final Timeout timeout = new Timeout(duration);
 
-            // Send a BatchedModifications message for the first transaction.
+            // Simulate the ForwardedReadyTransaction message for the first Tx that would be sent
+            // by the ShardTransaction.
 
-            shard.tell(newBatchedModifications(transactionID1, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            BatchedModificationsReply batchedReply = expectMsgClass(duration, BatchedModificationsReply.class);
-            assertEquals("getCohortPath", shard.path().toString(), batchedReply.getCohortPath());
-            assertEquals("getNumBatched", 1, batchedReply.getNumBatched());
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            ReadyTransactionReply readyReply = ReadyTransactionReply.fromSerializable(
+                    expectMsgClass(duration, ReadyTransactionReply.class));
+            assertEquals("Cohort path", shard.path().toString(), readyReply.getCohortPath());
 
             // Send the CanCommitTransaction message for the first Tx.
 
@@ -480,16 +483,15 @@ public class ShardTest extends AbstractShardTest {
                     expectMsgClass(duration, CanCommitTransactionReply.SERIALIZABLE_CLASS));
             assertEquals("Can commit", true, canCommitReply.getCanCommit());
 
-            // Send BatchedModifications for the next 2 Tx's.
+            // Send the ForwardedReadyTransaction for the next 2 Tx's.
 
-            shard.tell(newBatchedModifications(transactionID2, TestModel.OUTER_LIST_PATH,
-                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(newBatchedModifications(transactionID3, YangInstanceIdentifier.builder(
-                    TestModel.OUTER_LIST_PATH).nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
-                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID3, CURRENT_VERSION,
+                    cohort3, modification3, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message for the next 2 Tx's. These should get queued and
             // processed after the first Tx completes.
@@ -582,31 +584,20 @@ public class ShardTest extends AbstractShardTest {
 
             assertEquals("Commits complete", true, done);
 
-            InOrder inOrder = inOrder(mockCohort1.get(), mockCohort2.get(), mockCohort3.get());
-            inOrder.verify(mockCohort1.get()).canCommit();
-            inOrder.verify(mockCohort1.get()).preCommit();
-            inOrder.verify(mockCohort1.get()).commit();
-            inOrder.verify(mockCohort2.get()).canCommit();
-            inOrder.verify(mockCohort2.get()).preCommit();
-            inOrder.verify(mockCohort2.get()).commit();
-            inOrder.verify(mockCohort3.get()).canCommit();
-            inOrder.verify(mockCohort3.get()).preCommit();
-            inOrder.verify(mockCohort3.get()).commit();
+            InOrder inOrder = inOrder(cohort1, cohort2, cohort3);
+            inOrder.verify(cohort1).canCommit();
+            inOrder.verify(cohort1).preCommit();
+            inOrder.verify(cohort1).commit();
+            inOrder.verify(cohort2).canCommit();
+            inOrder.verify(cohort2).preCommit();
+            inOrder.verify(cohort2).commit();
+            inOrder.verify(cohort3).canCommit();
+            inOrder.verify(cohort3).preCommit();
+            inOrder.verify(cohort3).commit();
 
             // Verify data in the data store.
 
-            NormalizedNode<?, ?> outerList = readStore(shard, TestModel.OUTER_LIST_PATH);
-            assertNotNull(TestModel.OUTER_LIST_QNAME.getLocalName() + " not found", outerList);
-            assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " value is not Iterable",
-                    outerList.getValue() instanceof Iterable);
-            Object entry = ((Iterable<Object>)outerList.getValue()).iterator().next();
-            assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " entry is not MapEntryNode",
-                       entry instanceof MapEntryNode);
-            MapEntryNode mapEntry = (MapEntryNode)entry;
-            Optional<DataContainerChild<? extends PathArgument, ?>> idLeaf =
-                    mapEntry.getChild(new YangInstanceIdentifier.NodeIdentifier(TestModel.ID_QNAME));
-            assertTrue("Missing leaf " + TestModel.ID_QNAME.getLocalName(), idLeaf.isPresent());
-            assertEquals(TestModel.ID_QNAME.getLocalName() + " value", 1, idLeaf.get().getValue());
+            verifyOuterListEntry(shard, 1);
 
             verifyLastApplied(shard, 2);
 
@@ -615,25 +606,25 @@ public class ShardTest extends AbstractShardTest {
     }
 
     private BatchedModifications newBatchedModifications(String transactionID, YangInstanceIdentifier path,
-            NormalizedNode<?, ?> data, boolean ready) {
-        return newBatchedModifications(transactionID, null, path, data, ready);
+            NormalizedNode<?, ?> data, boolean ready, boolean doCommitOnReady) {
+        return newBatchedModifications(transactionID, null, path, data, ready, doCommitOnReady);
     }
 
     private BatchedModifications newBatchedModifications(String transactionID, String transactionChainID,
-            YangInstanceIdentifier path, NormalizedNode<?, ?> data, boolean ready) {
+            YangInstanceIdentifier path, NormalizedNode<?, ?> data, boolean ready, boolean doCommitOnReady) {
         BatchedModifications batched = new BatchedModifications(transactionID, CURRENT_VERSION, transactionChainID);
         batched.addModification(new WriteModification(path, data));
         batched.setReady(ready);
+        batched.setDoCommitOnReady(doCommitOnReady);
         return batched;
     }
 
-    @SuppressWarnings("unchecked")
     @Test
-    public void testMultipleBatchedModifications() throws Throwable {
+    public void testBatchedModificationsWithNoCommitOnReady() throws Throwable {
         new ShardTestKit(getSystem()) {{
             final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
                     newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
-                    "testMultipleBatchedModifications");
+                    "testBatchedModificationsWithNoCommitOnReady");
 
             waitUntilLeader(shard);
 
@@ -657,19 +648,19 @@ public class ShardTest extends AbstractShardTest {
             // Send a BatchedModifications to start a transaction.
 
             shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), false), getRef());
+                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), false, false), getRef());
             expectMsgClass(duration, BatchedModificationsReply.class);
 
             // Send a couple more BatchedModifications.
 
             shard.tell(newBatchedModifications(transactionID, TestModel.OUTER_LIST_PATH,
-                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(), false), getRef());
+                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(), false, false), getRef());
             expectMsgClass(duration, BatchedModificationsReply.class);
 
             shard.tell(newBatchedModifications(transactionID, YangInstanceIdentifier.builder(
                     TestModel.OUTER_LIST_PATH).nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
-                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1), true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message.
 
@@ -690,23 +681,85 @@ public class ShardTest extends AbstractShardTest {
 
             // Verify data in the data store.
 
-            NormalizedNode<?, ?> outerList = readStore(shard, TestModel.OUTER_LIST_PATH);
-            assertNotNull(TestModel.OUTER_LIST_QNAME.getLocalName() + " not found", outerList);
-            assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " value is not Iterable",
-                    outerList.getValue() instanceof Iterable);
-            Object entry = ((Iterable<Object>)outerList.getValue()).iterator().next();
-            assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " entry is not MapEntryNode",
-                       entry instanceof MapEntryNode);
-            MapEntryNode mapEntry = (MapEntryNode)entry;
-            Optional<DataContainerChild<? extends PathArgument, ?>> idLeaf =
-                    mapEntry.getChild(new YangInstanceIdentifier.NodeIdentifier(TestModel.ID_QNAME));
-            assertTrue("Missing leaf " + TestModel.ID_QNAME.getLocalName(), idLeaf.isPresent());
-            assertEquals(TestModel.ID_QNAME.getLocalName() + " value", 1, idLeaf.get().getValue());
+            verifyOuterListEntry(shard, 1);
+
+            shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        }};
+    }
+
+    @Test
+    public void testBatchedModificationsWithCommitOnReady() throws Throwable {
+        new ShardTestKit(getSystem()) {{
+            final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
+                    newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
+                    "testBatchedModificationsWithCommitOnReady");
+
+            waitUntilLeader(shard);
+
+            final String transactionID = "tx";
+            FiniteDuration duration = duration("5 seconds");
+
+            final AtomicReference<DOMStoreThreePhaseCommitCohort> mockCohort = new AtomicReference<>();
+            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
+                @Override
+                public DOMStoreThreePhaseCommitCohort decorate(String txID, DOMStoreThreePhaseCommitCohort actual) {
+                    if(mockCohort.get() == null) {
+                        mockCohort.set(createDelegatingMockCohort("cohort", actual));
+                    }
+
+                    return mockCohort.get();
+                }
+            };
+
+            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
+
+            // Send a BatchedModifications to start a transaction.
+
+            shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH,
+                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), false, false), getRef());
+            expectMsgClass(duration, BatchedModificationsReply.class);
+
+            // Send a couple more BatchedModifications.
+
+            shard.tell(newBatchedModifications(transactionID, TestModel.OUTER_LIST_PATH,
+                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(), false, false), getRef());
+            expectMsgClass(duration, BatchedModificationsReply.class);
+
+            shard.tell(newBatchedModifications(transactionID, YangInstanceIdentifier.builder(
+                    TestModel.OUTER_LIST_PATH).nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
+                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1), true, true), getRef());
+
+            expectMsgClass(duration, CommitTransactionReply.SERIALIZABLE_CLASS);
+
+            InOrder inOrder = inOrder(mockCohort.get());
+            inOrder.verify(mockCohort.get()).canCommit();
+            inOrder.verify(mockCohort.get()).preCommit();
+            inOrder.verify(mockCohort.get()).commit();
+
+            // Verify data in the data store.
+
+            verifyOuterListEntry(shard, 1);
 
             shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
         }};
     }
 
+    @SuppressWarnings("unchecked")
+    private void verifyOuterListEntry(final TestActorRef<Shard> shard, Object expIDValue) throws Exception {
+        NormalizedNode<?, ?> outerList = readStore(shard, TestModel.OUTER_LIST_PATH);
+        assertNotNull(TestModel.OUTER_LIST_QNAME.getLocalName() + " not found", outerList);
+        assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " value is not Iterable",
+                outerList.getValue() instanceof Iterable);
+        Object entry = ((Iterable<Object>)outerList.getValue()).iterator().next();
+        assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " entry is not MapEntryNode",
+                entry instanceof MapEntryNode);
+        MapEntryNode mapEntry = (MapEntryNode)entry;
+        Optional<DataContainerChild<? extends PathArgument, ?>> idLeaf =
+                mapEntry.getChild(new YangInstanceIdentifier.NodeIdentifier(TestModel.ID_QNAME));
+        assertTrue("Missing leaf " + TestModel.ID_QNAME.getLocalName(), idLeaf.isPresent());
+        assertEquals(TestModel.ID_QNAME.getLocalName() + " value", expIDValue, idLeaf.get().getValue());
+    }
+
     @Test
     public void testBatchedModificationsOnTransactionChain() throws Throwable {
         new ShardTestKit(getSystem()) {{
@@ -727,8 +780,8 @@ public class ShardTest extends AbstractShardTest {
             ContainerNode containerNode = ImmutableNodes.containerNode(TestModel.TEST_QNAME);
             YangInstanceIdentifier path = TestModel.TEST_PATH;
             shard.tell(newBatchedModifications(transactionID1, transactionChainID, path,
-                    containerNode, true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+                    containerNode, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Create a read Tx on the same chain.
 
@@ -800,6 +853,45 @@ public class ShardTest extends AbstractShardTest {
         }};
     }
 
+    @Test
+    public void testForwardedReadyTransactionWithImmediateCommit() throws Exception{
+        new ShardTestKit(getSystem()) {{
+            final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
+                    newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
+                    "testForwardedReadyTransactionWithImmediateCommit");
+
+            waitUntilLeader(shard);
+
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
+
+            String transactionID = "tx1";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            NormalizedNode<?, ?> containerNode = ImmutableNodes.containerNode(TestModel.TEST_QNAME);
+            DOMStoreThreePhaseCommitCohort cohort = setupMockWriteTransaction("cohort", dataStore,
+                    TestModel.TEST_PATH, containerNode, modification);
+
+            FiniteDuration duration = duration("5 seconds");
+
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
+
+            shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
+                    cohort, modification, true, true), getRef());
+
+            expectMsgClass(duration, ThreePhaseCommitCohortMessages.CommitTransactionReply.class);
+
+            InOrder inOrder = inOrder(cohort);
+            inOrder.verify(cohort).canCommit();
+            inOrder.verify(cohort).preCommit();
+            inOrder.verify(cohort).commit();
+
+            NormalizedNode<?, ?> actualNode = readStore(shard, TestModel.TEST_PATH);
+            assertEquals(TestModel.TEST_QNAME.getLocalName(), containerNode, actualNode);
+
+            shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        }};
+    }
+
     @Test
     public void testCommitWithPersistenceDisabled() throws Throwable {
         dataStoreContextBuilder.persistent(false);
@@ -810,14 +902,24 @@ public class ShardTest extends AbstractShardTest {
 
             waitUntilLeader(shard);
 
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
+
+            // Setup a simulated transactions with a mock cohort.
+
             String transactionID = "tx";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            NormalizedNode<?, ?> containerNode = ImmutableNodes.containerNode(TestModel.TEST_QNAME);
+            DOMStoreThreePhaseCommitCohort cohort = setupMockWriteTransaction("cohort", dataStore,
+                    TestModel.TEST_PATH, containerNode, modification);
+
             FiniteDuration duration = duration("5 seconds");
 
-            // Send a BatchedModifications to start a transaction.
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
 
-            NormalizedNode<?, ?> containerNode = ImmutableNodes.containerNode(TestModel.TEST_QNAME);
-            shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH, containerNode, true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message.
 
@@ -831,6 +933,11 @@ public class ShardTest extends AbstractShardTest {
             shard.tell(new CommitTransaction(transactionID).toSerializable(), getRef());
             expectMsgClass(duration, CommitTransactionReply.SERIALIZABLE_CLASS);
 
+            InOrder inOrder = inOrder(cohort);
+            inOrder.verify(cohort).canCommit();
+            inOrder.verify(cohort).preCommit();
+            inOrder.verify(cohort).commit();
+
             NormalizedNode<?, ?> actualNode = readStore(shard, TestModel.TEST_PATH);
             assertEquals(TestModel.TEST_QNAME.getLocalName(), containerNode, actualNode);
 
@@ -863,8 +970,8 @@ public class ShardTest extends AbstractShardTest {
                 // by the ShardTransaction.
 
                 shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
-                        cohort, modification, true), getRef());
-                expectMsgClass(duration, ReadyTransactionReply.SERIALIZABLE_CLASS);
+                        cohort, modification, true, false), getRef());
+                expectMsgClass(duration, ReadyTransactionReply.class);
 
                 // Send the CanCommitTransaction message.
 
@@ -918,8 +1025,8 @@ public class ShardTest extends AbstractShardTest {
                 // by the ShardTransaction.
 
                 shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
-                        cohort, modification, true), getRef());
-                expectMsgClass(duration, ReadyTransactionReply.SERIALIZABLE_CLASS);
+                        cohort, modification, true, false), getRef());
+                expectMsgClass(duration, ReadyTransactionReply.class);
 
                 // Send the CanCommitTransaction message.
 
@@ -958,40 +1065,34 @@ public class ShardTest extends AbstractShardTest {
 
             waitUntilLeader(shard);
 
-            // Setup 2 mock cohorts. The first one fails in the commit phase.
+            // Setup 2 simulated transactions with mock cohorts. The first one fails in the
+            // commit phase.
 
-            final String transactionID1 = "tx1";
-            final DOMStoreThreePhaseCommitCohort cohort1 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
             doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort1).canCommit();
             doReturn(Futures.immediateFuture(null)).when(cohort1).preCommit();
             doReturn(Futures.immediateFailedFuture(new IllegalStateException("mock"))).when(cohort1).commit();
 
-            final String transactionID2 = "tx2";
-            final DOMStoreThreePhaseCommitCohort cohort2 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort2");
+            String transactionID2 = "tx2";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort2 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort2");
             doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort2).canCommit();
 
-            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
-                @Override
-                public DOMStoreThreePhaseCommitCohort decorate(String transactionID,
-                        DOMStoreThreePhaseCommitCohort actual) {
-                    return transactionID1.equals(transactionID) ? cohort1 : cohort2;
-                }
-            };
-
-            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
-
             FiniteDuration duration = duration("5 seconds");
             final Timeout timeout = new Timeout(duration);
 
-            // Send BatchedModifications to start and ready each transaction.
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
 
-            shard.tell(newBatchedModifications(transactionID1, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(newBatchedModifications(transactionID2, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message for the first Tx.
 
@@ -1043,45 +1144,66 @@ public class ShardTest extends AbstractShardTest {
 
             waitUntilLeader(shard);
 
-            String transactionID = "tx1";
-            final DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
-            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
-            doReturn(Futures.immediateFailedFuture(new IllegalStateException("mock"))).when(cohort).preCommit();
-
-            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
-                @Override
-                public DOMStoreThreePhaseCommitCohort decorate(String transactionID,
-                        DOMStoreThreePhaseCommitCohort actual) {
-                    return cohort;
-                }
-            };
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort1).canCommit();
+            doReturn(Futures.immediateFailedFuture(new IllegalStateException("mock"))).when(cohort1).preCommit();
 
-            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
+            String transactionID2 = "tx2";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort2 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort2");
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort2).canCommit();
 
             FiniteDuration duration = duration("5 seconds");
+            final Timeout timeout = new Timeout(duration);
 
-            // Send BatchedModifications to start and ready a transaction.
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
 
-            shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            // Send the CanCommitTransaction message.
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(new CanCommitTransaction(transactionID).toSerializable(), getRef());
+            // Send the CanCommitTransaction message for the first Tx.
+
+            shard.tell(new CanCommitTransaction(transactionID1).toSerializable(), getRef());
             CanCommitTransactionReply canCommitReply = CanCommitTransactionReply.fromSerializable(
                     expectMsgClass(duration, CanCommitTransactionReply.SERIALIZABLE_CLASS));
             assertEquals("Can commit", true, canCommitReply.getCanCommit());
 
-            // Send the CommitTransaction message. This should send back an error
-            // for preCommit failure.
+            // Send the CanCommitTransaction message for the 2nd Tx. This should get queued and
+            // processed after the first Tx completes.
 
-            shard.tell(new CommitTransaction(transactionID).toSerializable(), getRef());
+            Future<Object> canCommitFuture = Patterns.ask(shard,
+                    new CanCommitTransaction(transactionID2).toSerializable(), timeout);
+
+            // Send the CommitTransaction message for the first Tx. This should send back an error
+            // and trigger the 2nd Tx to proceed.
+
+            shard.tell(new CommitTransaction(transactionID1).toSerializable(), getRef());
             expectMsgClass(duration, akka.actor.Status.Failure.class);
 
-            InOrder inOrder = inOrder(cohort);
-            inOrder.verify(cohort).canCommit();
-            inOrder.verify(cohort).preCommit();
+            // Wait for the 2nd Tx to complete the canCommit phase.
+
+            final CountDownLatch latch = new CountDownLatch(1);
+            canCommitFuture.onComplete(new OnComplete<Object>() {
+                @Override
+                public void onComplete(final Throwable t, final Object resp) {
+                    latch.countDown();
+                }
+            }, getSystem().dispatcher());
+
+            assertEquals("2nd CanCommit complete", true, latch.await(5, TimeUnit.SECONDS));
+
+            InOrder inOrder = inOrder(cohort1, cohort2);
+            inOrder.verify(cohort1).canCommit();
+            inOrder.verify(cohort1).preCommit();
+            inOrder.verify(cohort2).canCommit();
 
             shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
         }};
@@ -1098,31 +1220,173 @@ public class ShardTest extends AbstractShardTest {
 
             final FiniteDuration duration = duration("5 seconds");
 
-            String transactionID = "tx1";
-            final DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
             doReturn(Futures.immediateFailedFuture(new IllegalStateException("mock"))).when(cohort).canCommit();
 
-            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
-                @Override
-                public DOMStoreThreePhaseCommitCohort decorate(String transactionID,
-                        DOMStoreThreePhaseCommitCohort actual) {
-                    return cohort;
-                }
-            };
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
 
-            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            // Send BatchedModifications to start and ready a transaction.
+            // Send the CanCommitTransaction message.
 
-            shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new CanCommitTransaction(transactionID1).toSerializable(), getRef());
+            expectMsgClass(duration, akka.actor.Status.Failure.class);
+
+            // Send another can commit to ensure the failed one got cleaned up.
+
+            reset(cohort);
+
+            String transactionID2 = "tx2";
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
+
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
+
+            shard.tell(new CanCommitTransaction(transactionID2).toSerializable(), getRef());
+            CanCommitTransactionReply reply = CanCommitTransactionReply.fromSerializable(
+                    expectMsgClass(CanCommitTransactionReply.SERIALIZABLE_CLASS));
+            assertEquals("getCanCommit", true, reply.getCanCommit());
+
+            shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        }};
+    }
+
+    @Test
+    public void testCanCommitPhaseFalseResponse() throws Throwable {
+        new ShardTestKit(getSystem()) {{
+            final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
+                    newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
+                    "testCanCommitPhaseFalseResponse");
+
+            waitUntilLeader(shard);
+
+            final FiniteDuration duration = duration("5 seconds");
+
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            doReturn(Futures.immediateFuture(Boolean.FALSE)).when(cohort).canCommit();
+
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
+
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message.
 
-            shard.tell(new CanCommitTransaction(transactionID).toSerializable(), getRef());
+            shard.tell(new CanCommitTransaction(transactionID1).toSerializable(), getRef());
+            CanCommitTransactionReply reply = CanCommitTransactionReply.fromSerializable(
+                    expectMsgClass(CanCommitTransactionReply.SERIALIZABLE_CLASS));
+            assertEquals("getCanCommit", false, reply.getCanCommit());
+
+            // Send another can commit to ensure the failed one got cleaned up.
+
+            reset(cohort);
+
+            String transactionID2 = "tx2";
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
+
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
+
+            shard.tell(new CanCommitTransaction(transactionID2).toSerializable(), getRef());
+            reply = CanCommitTransactionReply.fromSerializable(
+                    expectMsgClass(CanCommitTransactionReply.SERIALIZABLE_CLASS));
+            assertEquals("getCanCommit", true, reply.getCanCommit());
+
+            shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        }};
+    }
+
+    @Test
+    public void testImmediateCommitWithCanCommitPhaseFailure() throws Throwable {
+        new ShardTestKit(getSystem()) {{
+            final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
+                    newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
+                    "testImmediateCommitWithCanCommitPhaseFailure");
+
+            waitUntilLeader(shard);
+
+            final FiniteDuration duration = duration("5 seconds");
+
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            doReturn(Futures.immediateFailedFuture(new IllegalStateException("mock"))).when(cohort).canCommit();
+
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
+
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort, modification, true, true), getRef());
+
             expectMsgClass(duration, akka.actor.Status.Failure.class);
 
+            // Send another can commit to ensure the failed one got cleaned up.
+
+            reset(cohort);
+
+            String transactionID2 = "tx2";
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
+            doReturn(Futures.immediateFuture(null)).when(cohort).preCommit();
+            doReturn(Futures.immediateFuture(null)).when(cohort).commit();
+
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort, modification, true, true), getRef());
+
+            expectMsgClass(duration, CommitTransactionReply.SERIALIZABLE_CLASS);
+
+            shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        }};
+    }
+
+    @Test
+    public void testImmediateCommitWithCanCommitPhaseFalseResponse() throws Throwable {
+        new ShardTestKit(getSystem()) {{
+            final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
+                    newShardProps().withDispatcher(Dispatchers.DefaultDispatcherId()),
+                    "testImmediateCommitWithCanCommitPhaseFalseResponse");
+
+            waitUntilLeader(shard);
+
+            final FiniteDuration duration = duration("5 seconds");
+
+            String transactionID = "tx1";
+            MutableCompositeModification modification = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            doReturn(Futures.immediateFuture(Boolean.FALSE)).when(cohort).canCommit();
+
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
+
+            shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
+                    cohort, modification, true, true), getRef());
+
+            expectMsgClass(duration, akka.actor.Status.Failure.class);
+
+            // Send another can commit to ensure the failed one got cleaned up.
+
+            reset(cohort);
+
+            String transactionID2 = "tx2";
+            doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
+            doReturn(Futures.immediateFuture(null)).when(cohort).preCommit();
+            doReturn(Futures.immediateFuture(null)).when(cohort).commit();
+
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort, modification, true, true), getRef());
+
+            expectMsgClass(duration, CommitTransactionReply.SERIALIZABLE_CLASS);
+
             shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
         }};
     }
@@ -1137,7 +1401,7 @@ public class ShardTest extends AbstractShardTest {
             waitUntilLeader(shard);
 
             final FiniteDuration duration = duration("5 seconds");
-            InMemoryDOMDataStore dataStore = shard.underlyingActor().getDataStore();
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
 
             final String transactionID = "tx1";
             Function<DOMStoreThreePhaseCommitCohort,ListenableFuture<Void>> preCommit =
@@ -1160,9 +1424,14 @@ public class ShardTest extends AbstractShardTest {
                 }
             };
 
-            shard.tell(newBatchedModifications(transactionID, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            MutableCompositeModification modification = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort = setupMockWriteTransaction("cohort1", dataStore,
+                    TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME),
+                    modification, preCommit);
+
+            shard.tell(new ForwardedReadyTransaction(transactionID, CURRENT_VERSION,
+                    cohort, modification, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             shard.tell(new CanCommitTransaction(transactionID).toSerializable(), getRef());
             CanCommitTransactionReply canCommitReply = CanCommitTransactionReply.fromSerializable(
@@ -1196,26 +1465,42 @@ public class ShardTest extends AbstractShardTest {
 
             final FiniteDuration duration = duration("5 seconds");
 
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
+
             writeToStore(shard, TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME));
             writeToStore(shard, TestModel.OUTER_LIST_PATH,
                     ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build());
 
-            // Create and ready the 1st Tx - will timeout
+            // Create 1st Tx - will timeout
 
             String transactionID1 = "tx1";
-            shard.tell(newBatchedModifications(transactionID1, YangInstanceIdentifier.builder(
-                    TestModel.OUTER_LIST_PATH).nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
-                ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = setupMockWriteTransaction("cohort1", dataStore,
+                    YangInstanceIdentifier.builder(TestModel.OUTER_LIST_PATH)
+                        .nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1).build(),
+                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 1),
+                    modification1);
 
-            // Create and ready the 2nd Tx
+            // Create 2nd Tx
 
-            String transactionID2 = "tx2";
+            String transactionID2 = "tx3";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
             YangInstanceIdentifier listNodePath = YangInstanceIdentifier.builder(TestModel.OUTER_LIST_PATH)
-                    .nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 2).build();
-            shard.tell(newBatchedModifications(transactionID2, listNodePath,
-                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 2), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+                .nodeWithKey(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 2).build();
+            DOMStoreThreePhaseCommitCohort cohort2 = setupMockWriteTransaction("cohort3", dataStore,
+                    listNodePath,
+                    ImmutableNodes.mapEntry(TestModel.OUTER_LIST_QNAME, TestModel.ID_QNAME, 2),
+                    modification2);
+
+            // Ready the Tx's
+
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
+
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // canCommit 1st Tx. We don't send the commit so it should timeout.
 
@@ -1227,6 +1512,11 @@ public class ShardTest extends AbstractShardTest {
             shard.tell(new CanCommitTransaction(transactionID2).toSerializable(), getRef());
             expectMsgClass(duration, CanCommitTransactionReply.SERIALIZABLE_CLASS);
 
+            // Try to commit the 1st Tx - should fail as it's not the current Tx.
+
+            shard.tell(new CommitTransaction(transactionID1).toSerializable(), getRef());
+            expectMsgClass(duration, akka.actor.Status.Failure.class);
+
             // Commit the 2nd Tx.
 
             shard.tell(new CommitTransaction(transactionID2).toSerializable(), getRef());
@@ -1252,23 +1542,38 @@ public class ShardTest extends AbstractShardTest {
 
             final FiniteDuration duration = duration("5 seconds");
 
+            ShardDataTree dataStore = shard.underlyingActor().getDataStore();
+
             String transactionID1 = "tx1";
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = setupMockWriteTransaction("cohort1", dataStore,
+                    TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME), modification1);
+
             String transactionID2 = "tx2";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort2 = setupMockWriteTransaction("cohort2", dataStore,
+                    TestModel.OUTER_LIST_PATH,
+                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(),
+                    modification2);
+
             String transactionID3 = "tx3";
+            MutableCompositeModification modification3 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort3 = setupMockWriteTransaction("cohort3", dataStore,
+                    TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME), modification3);
 
-            // Send a BatchedModifications to start transactions and ready them.
+            // Ready the Tx's
 
-            shard.tell(newBatchedModifications(transactionID1, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(newBatchedModifications(transactionID2,TestModel.OUTER_LIST_PATH,
-                    ImmutableNodes.mapNodeBuilder(TestModel.OUTER_LIST_QNAME).build(), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(newBatchedModifications(transactionID3, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID3, CURRENT_VERSION,
+                    cohort3, modification3, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // canCommit 1st Tx.
 
@@ -1313,37 +1618,30 @@ public class ShardTest extends AbstractShardTest {
 
             // Setup 2 simulated transactions with mock cohorts. The first one will be aborted.
 
-            final String transactionID1 = "tx1";
-            final DOMStoreThreePhaseCommitCohort cohort1 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
+            String transactionID1 = "tx1";
+            MutableCompositeModification modification1 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort1 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort1");
             doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort1).canCommit();
             doReturn(Futures.immediateFuture(null)).when(cohort1).abort();
 
-            final String transactionID2 = "tx2";
-            final DOMStoreThreePhaseCommitCohort cohort2 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort2");
+            String transactionID2 = "tx2";
+            MutableCompositeModification modification2 = new MutableCompositeModification();
+            DOMStoreThreePhaseCommitCohort cohort2 = mock(DOMStoreThreePhaseCommitCohort.class, "cohort2");
             doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort2).canCommit();
 
             FiniteDuration duration = duration("5 seconds");
             final Timeout timeout = new Timeout(duration);
 
-            ShardCommitCoordinator.CohortDecorator cohortDecorator = new ShardCommitCoordinator.CohortDecorator() {
-                @Override
-                public DOMStoreThreePhaseCommitCohort decorate(String transactionID,
-                        DOMStoreThreePhaseCommitCohort actual) {
-                    return transactionID1.equals(transactionID) ? cohort1 : cohort2;
-                }
-            };
+            // Simulate the ForwardedReadyTransaction messages that would be sent
+            // by the ShardTransaction.
 
-            shard.underlyingActor().getCommitCoordinator().setCohortDecorator(cohortDecorator);
-
-            // Send BatchedModifications to start and ready each transaction.
+            shard.tell(new ForwardedReadyTransaction(transactionID1, CURRENT_VERSION,
+                    cohort1, modification1, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
-            shard.tell(newBatchedModifications(transactionID1, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
-
-            shard.tell(newBatchedModifications(transactionID2, TestModel.TEST_PATH,
-                    ImmutableNodes.containerNode(TestModel.TEST_QNAME), true), getRef());
-            expectMsgClass(duration, BatchedModificationsReply.class);
+            shard.tell(new ForwardedReadyTransaction(transactionID2, CURRENT_VERSION,
+                    cohort2, modification2, true, false), getRef());
+            expectMsgClass(duration, ReadyTransactionReply.class);
 
             // Send the CanCommitTransaction message for the first Tx.
 
@@ -1389,6 +1687,8 @@ public class ShardTest extends AbstractShardTest {
     @SuppressWarnings("serial")
     public void testCreateSnapshot(final boolean persistent, final String shardActorName) throws Exception{
 
+        final AtomicReference<CountDownLatch> latch = new AtomicReference<>(new CountDownLatch(1));
+
         final AtomicReference<Object> savedSnapshot = new AtomicReference<>();
         class TestPersistentDataProvider extends DelegatingPersistentDataProvider {
             TestPersistentDataProvider(DataPersistenceProvider delegate) {
@@ -1405,8 +1705,6 @@ public class ShardTest extends AbstractShardTest {
         dataStoreContextBuilder.persistent(persistent);
 
         new ShardTestKit(getSystem()) {{
-            final AtomicReference<CountDownLatch> latch = new AtomicReference<>(new CountDownLatch(1));
-
             class TestShard extends Shard {
 
                 protected TestShard(ShardIdentifier name, Map<String, String> peerAddresses,
@@ -1416,9 +1714,12 @@ public class ShardTest extends AbstractShardTest {
                 }
 
                 @Override
-                protected void commitSnapshot(final long sequenceNumber) {
-                    super.commitSnapshot(sequenceNumber);
-                    latch.get().countDown();
+                public void handleCommand(Object message) {
+                    super.handleCommand(message);
+
+                    if (message instanceof SaveSnapshotSuccess || message.equals("commit_snapshot")) {
+                        latch.get().countDown();
+                    }
                 }
 
                 @Override