CDS: Split out TransactionFutureCallback
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / main / java / org / opendaylight / controller / cluster / datastore / TransactionProxy.java
index 9f48ef96cf517e265970b744b87af014dc51cbca..a0987cd5d63943979985527794dbe8471c0afe78 100644 (file)
@@ -12,45 +12,31 @@ import akka.actor.ActorSelection;
 import akka.dispatch.Mapper;
 import akka.dispatch.OnComplete;
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.FinalizablePhantomReference;
-import com.google.common.base.FinalizableReferenceQueue;
 import com.google.common.base.Optional;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.util.concurrent.CheckedFuture;
-import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.SettableFuture;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.Set;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
-import javax.annotation.concurrent.GuardedBy;
-import org.opendaylight.controller.cluster.datastore.exceptions.NoShardLeaderException;
+import org.opendaylight.controller.cluster.datastore.compat.PreLithiumTransactionContextImpl;
 import org.opendaylight.controller.cluster.datastore.identifiers.TransactionIdentifier;
-import org.opendaylight.controller.cluster.datastore.messages.CloseTransaction;
-import org.opendaylight.controller.cluster.datastore.messages.CreateTransaction;
-import org.opendaylight.controller.cluster.datastore.messages.CreateTransactionReply;
-import org.opendaylight.controller.cluster.datastore.messages.DataExists;
-import org.opendaylight.controller.cluster.datastore.messages.DataExistsReply;
-import org.opendaylight.controller.cluster.datastore.messages.DeleteData;
-import org.opendaylight.controller.cluster.datastore.messages.MergeData;
-import org.opendaylight.controller.cluster.datastore.messages.ReadData;
-import org.opendaylight.controller.cluster.datastore.messages.ReadDataReply;
-import org.opendaylight.controller.cluster.datastore.messages.ReadyTransaction;
-import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
-import org.opendaylight.controller.cluster.datastore.messages.SerializableMessage;
-import org.opendaylight.controller.cluster.datastore.messages.VersionedSerializableMessage;
-import org.opendaylight.controller.cluster.datastore.messages.WriteData;
 import org.opendaylight.controller.cluster.datastore.shardstrategy.ShardStrategyFactory;
 import org.opendaylight.controller.cluster.datastore.utils.ActorContext;
+import org.opendaylight.controller.cluster.datastore.utils.NormalizedNodeAggregator;
 import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
+import org.opendaylight.controller.sal.core.spi.data.AbstractDOMStoreTransaction;
 import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadWriteTransaction;
-import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
 import org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
@@ -59,7 +45,6 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import scala.concurrent.Future;
 import scala.concurrent.Promise;
-import scala.concurrent.duration.FiniteDuration;
 
 /**
  * TransactionProxy acts as a proxy for one or more transactions that were created on a remote shard
@@ -73,12 +58,29 @@ import scala.concurrent.duration.FiniteDuration;
  * shards will be executed.
  * </p>
  */
-public class TransactionProxy implements DOMStoreReadWriteTransaction {
+public class TransactionProxy extends AbstractDOMStoreTransaction<TransactionIdentifier> implements DOMStoreReadWriteTransaction {
 
     public static enum TransactionType {
         READ_ONLY,
         WRITE_ONLY,
-        READ_WRITE
+        READ_WRITE;
+
+        // Cache all values
+        private static final TransactionType[] VALUES = values();
+
+        public static TransactionType fromInt(final int type) {
+            try {
+                return VALUES[type];
+            } catch (IndexOutOfBoundsException e) {
+                throw new IllegalArgumentException("In TransactionType enum value " + type, e);
+            }
+        }
+    }
+
+    private static enum TransactionState {
+        OPEN,
+        READY,
+        CLOSED,
     }
 
     static final Mapper<Throwable, Throwable> SAME_FAILURE_TRANSFORMER =
@@ -93,78 +95,6 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
 
     private static final Logger LOG = LoggerFactory.getLogger(TransactionProxy.class);
 
-    /**
-     * Time interval in between transaction create retries.
-     */
-    private static final FiniteDuration CREATE_TX_TRY_INTERVAL =
-            FiniteDuration.create(1, TimeUnit.SECONDS);
-
-    /**
-     * Used to enqueue the PhantomReferences for read-only TransactionProxy instances. The
-     * FinalizableReferenceQueue is safe to use statically in an OSGi environment as it uses some
-     * trickery to clean up its internal thread when the bundle is unloaded.
-     */
-    private static final FinalizableReferenceQueue phantomReferenceQueue =
-                                                                  new FinalizableReferenceQueue();
-
-    /**
-     * This stores the TransactionProxyCleanupPhantomReference instances statically, This is
-     * necessary because PhantomReferences need a hard reference so they're not garbage collected.
-     * Once finalized, the TransactionProxyCleanupPhantomReference removes itself from this map
-     * and thus becomes eligible for garbage collection.
-     */
-    private static final Map<TransactionProxyCleanupPhantomReference,
-                             TransactionProxyCleanupPhantomReference> phantomReferenceCache =
-                                                                        new ConcurrentHashMap<>();
-
-    /**
-     * A PhantomReference that closes remote transactions for a TransactionProxy when it's
-     * garbage collected. This is used for read-only transactions as they're not explicitly closed
-     * by clients. So the only way to detect that a transaction is no longer in use and it's safe
-     * to clean up is when it's garbage collected. It's inexact as to when an instance will be GC'ed
-     * but TransactionProxy instances should generally be short-lived enough to avoid being moved
-     * to the old generation space and thus should be cleaned up in a timely manner as the GC
-     * runs on the young generation (eden, swap1...) space much more frequently.
-     */
-    private static class TransactionProxyCleanupPhantomReference
-                                           extends FinalizablePhantomReference<TransactionProxy> {
-
-        private final List<ActorSelection> remoteTransactionActors;
-        private final AtomicBoolean remoteTransactionActorsMB;
-        private final ActorContext actorContext;
-        private final TransactionIdentifier identifier;
-
-        protected TransactionProxyCleanupPhantomReference(TransactionProxy referent) {
-            super(referent, phantomReferenceQueue);
-
-            // Note we need to cache the relevant fields from the TransactionProxy as we can't
-            // have a hard reference to the TransactionProxy instance itself.
-
-            remoteTransactionActors = referent.remoteTransactionActors;
-            remoteTransactionActorsMB = referent.remoteTransactionActorsMB;
-            actorContext = referent.actorContext;
-            identifier = referent.identifier;
-        }
-
-        @Override
-        public void finalizeReferent() {
-            LOG.trace("Cleaning up {} Tx actors for TransactionProxy {}",
-                    remoteTransactionActors.size(), identifier);
-
-            phantomReferenceCache.remove(this);
-
-            // Access the memory barrier volatile to ensure all previous updates to the
-            // remoteTransactionActors list are visible to this thread.
-
-            if(remoteTransactionActorsMB.get()) {
-                for(ActorSelection actor : remoteTransactionActors) {
-                    LOG.trace("Sending CloseTransaction to {}", actor);
-                    actorContext.sendOperationAsync(actor, CloseTransaction.INSTANCE.toSerializable());
-                }
-            }
-        }
-    }
-
     /**
      * Stores the remote Tx actors for each requested data store path to be used by the
      * PhantomReference to close the remote Tx's. This is only used for read-only Tx's. The
@@ -172,8 +102,8 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
      * remoteTransactionActors list so they will be visible to the thread accessing the
      * PhantomReference.
      */
-    private List<ActorSelection> remoteTransactionActors;
-    private AtomicBoolean remoteTransactionActorsMB;
+    List<ActorSelection> remoteTransactionActors;
+    volatile AtomicBoolean remoteTransactionActorsMB;
 
     /**
      * Stores the create transaction results per shard.
@@ -181,20 +111,21 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
     private final Map<String, TransactionFutureCallback> txFutureCallbackMap = new HashMap<>();
 
     private final TransactionType transactionType;
-    private final ActorContext actorContext;
-    private final TransactionIdentifier identifier;
+    final ActorContext actorContext;
     private final String transactionChainId;
     private final SchemaContext schemaContext;
-    private boolean inReadyState;
-    private final Semaphore operationLimiter;
-    private final OperationCompleter operationCompleter;
+    private TransactionState state = TransactionState.OPEN;
+
+    private volatile boolean initialized;
+    private Semaphore operationLimiter;
+    private OperationCompleter operationCompleter;
 
     public TransactionProxy(ActorContext actorContext, TransactionType transactionType) {
         this(actorContext, transactionType, "");
     }
 
-    public TransactionProxy(ActorContext actorContext, TransactionType transactionType,
-            String transactionChainId) {
+    public TransactionProxy(ActorContext actorContext, TransactionType transactionType, String transactionChainId) {
+        super(createIdentifier(actorContext));
         this.actorContext = Preconditions.checkNotNull(actorContext,
             "actorContext should not be null");
         this.transactionType = Preconditions.checkNotNull(transactionType,
@@ -203,45 +134,16 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
             "schemaContext should not be null");
         this.transactionChainId = transactionChainId;
 
-        String memberName = actorContext.getCurrentMemberName();
-        if(memberName == null){
-            memberName = "UNKNOWN-MEMBER";
-        }
-
-        this.identifier = TransactionIdentifier.builder().memberName(memberName).counter(
-            counter.getAndIncrement()).build();
-
-        if(transactionType == TransactionType.READ_ONLY) {
-            // Read-only Tx's aren't explicitly closed by the client so we create a PhantomReference
-            // to close the remote Tx's when this instance is no longer in use and is garbage
-            // collected.
-
-            remoteTransactionActors = Lists.newArrayList();
-            remoteTransactionActorsMB = new AtomicBoolean();
-
-            TransactionProxyCleanupPhantomReference cleanup =
-                new TransactionProxyCleanupPhantomReference(this);
-            phantomReferenceCache.put(cleanup, cleanup);
-        }
-
-        // Note : Currently mailbox-capacity comes from akka.conf and not from the config-subsystem
-        this.operationLimiter = new Semaphore(actorContext.getTransactionOutstandingOperationLimit());
-        this.operationCompleter = new OperationCompleter(operationLimiter);
-
-        LOG.debug("Created txn {} of type {} on chain {}", identifier, transactionType, transactionChainId);
+        LOG.debug("Created txn {} of type {} on chain {}", getIdentifier(), transactionType, transactionChainId);
     }
 
-    @VisibleForTesting
-    List<Future<Object>> getRecordedOperationFutures() {
-        List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
-        for(TransactionFutureCallback txFutureCallback : txFutureCallbackMap.values()) {
-            TransactionContext transactionContext = txFutureCallback.getTransactionContext();
-            if(transactionContext != null) {
-                recordedOperationFutures.addAll(transactionContext.getRecordedOperationFutures());
-            }
+    private static TransactionIdentifier createIdentifier(ActorContext actorContext) {
+        String memberName = actorContext.getCurrentMemberName();
+        if (memberName == null) {
+            memberName = "UNKNOWN-MEMBER";
         }
 
-        return recordedOperationFutures;
+        return new TransactionIdentifier(memberName, counter.getAndIncrement());
     }
 
     @VisibleForTesting
@@ -256,24 +158,72 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         return false;
     }
 
+    private boolean isRootPath(YangInstanceIdentifier path){
+        return !path.getPathArguments().iterator().hasNext();
+    }
+
     @Override
     public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> read(final YangInstanceIdentifier path) {
 
         Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
                 "Read operation on write-only transaction is not allowed");
 
-        LOG.debug("Tx {} read {}", identifier, path);
+        LOG.debug("Tx {} read {}", getIdentifier(), path);
 
-        throttleOperation();
+        final SettableFuture<Optional<NormalizedNode<?, ?>>> proxyFuture = SettableFuture.create();
 
-        TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
-        return txFutureCallback.enqueueReadOperation(new ReadOperation<Optional<NormalizedNode<?, ?>>>() {
+        if(isRootPath(path)){
+            readAllData(path, proxyFuture);
+        } else {
+            throttleOperation();
+
+            TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
+            txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
+                @Override
+                public void invoke(TransactionContext transactionContext) {
+                    transactionContext.readData(path, proxyFuture);
+                }
+            });
+
+        }
+
+        return MappingCheckedFuture.create(proxyFuture, ReadFailedException.MAPPER);
+    }
+
+    private void readAllData(final YangInstanceIdentifier path,
+                             final SettableFuture<Optional<NormalizedNode<?, ?>>> proxyFuture) {
+        Set<String> allShardNames = actorContext.getConfiguration().getAllShardNames();
+        List<SettableFuture<Optional<NormalizedNode<?, ?>>>> futures = new ArrayList<>(allShardNames.size());
+
+        for(String shardName : allShardNames){
+            final SettableFuture<Optional<NormalizedNode<?, ?>>> subProxyFuture = SettableFuture.create();
+
+            throttleOperation();
+
+            TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(shardName);
+            txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
+                @Override
+                public void invoke(TransactionContext transactionContext) {
+                    transactionContext.readData(path, subProxyFuture);
+                }
+            });
+
+            futures.add(subProxyFuture);
+        }
+
+        final ListenableFuture<List<Optional<NormalizedNode<?, ?>>>> future = Futures.allAsList(futures);
+
+        future.addListener(new Runnable() {
             @Override
-            public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> invoke(
-                    TransactionContext transactionContext) {
-                return transactionContext.readData(path);
+            public void run() {
+                try {
+                    proxyFuture.set(NormalizedNodeAggregator.aggregate(YangInstanceIdentifier.builder().build(),
+                            future.get(), actorContext.getSchemaContext()));
+                } catch (InterruptedException | ExecutionException e) {
+                    proxyFuture.setException(e);
+                }
             }
-        });
+        }, actorContext.getActorSystem().dispatcher());
     }
 
     @Override
@@ -282,24 +232,27 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
                 "Exists operation on write-only transaction is not allowed");
 
-        LOG.debug("Tx {} exists {}", identifier, path);
+        LOG.debug("Tx {} exists {}", getIdentifier(), path);
 
         throttleOperation();
 
+        final SettableFuture<Boolean> proxyFuture = SettableFuture.create();
+
         TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
-        return txFutureCallback.enqueueReadOperation(new ReadOperation<Boolean>() {
+        txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
             @Override
-            public CheckedFuture<Boolean, ReadFailedException> invoke(TransactionContext transactionContext) {
-                return transactionContext.dataExists(path);
+            public void invoke(TransactionContext transactionContext) {
+                transactionContext.dataExists(path, proxyFuture);
             }
         });
-    }
 
+        return MappingCheckedFuture.create(proxyFuture, ReadFailedException.MAPPER);
+    }
 
     private void checkModificationState() {
         Preconditions.checkState(transactionType != TransactionType.READ_ONLY,
                 "Modification operation on read-only transaction is not allowed");
-        Preconditions.checkState(!inReadyState,
+        Preconditions.checkState(state == TransactionState.OPEN,
                 "Transaction is sealed - further modifications are not allowed");
     }
 
@@ -308,8 +261,19 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
     }
 
     private void throttleOperation(int acquirePermits) {
+        if(!initialized) {
+            // Note : Currently mailbox-capacity comes from akka.conf and not from the config-subsystem
+            operationLimiter = new Semaphore(actorContext.getTransactionOutstandingOperationLimit());
+            operationCompleter = new OperationCompleter(operationLimiter);
+
+            // Make sure we write this last because it's volatile and will also publish the non-volatile writes
+            // above as well so they'll be visible to other threads.
+            initialized = true;
+        }
+
         try {
-            if(!operationLimiter.tryAcquire(acquirePermits, actorContext.getDatastoreContext().getOperationTimeoutInSeconds(), TimeUnit.SECONDS)){
+            if(!operationLimiter.tryAcquire(acquirePermits,
+                    actorContext.getDatastoreContext().getOperationTimeoutInSeconds(), TimeUnit.SECONDS)){
                 LOG.warn("Failed to acquire operation permit for transaction {}", getIdentifier());
             }
         } catch (InterruptedException e) {
@@ -321,18 +285,21 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         }
     }
 
+    final void ensureInitializied() {
+        Preconditions.checkState(initialized, "Transaction %s was not propertly initialized.", getIdentifier());
+    }
 
     @Override
     public void write(final YangInstanceIdentifier path, final NormalizedNode<?, ?> data) {
 
         checkModificationState();
 
-        LOG.debug("Tx {} write {}", identifier, path);
+        LOG.debug("Tx {} write {}", getIdentifier(), path);
 
         throttleOperation();
 
         TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
-        txFutureCallback.enqueueModifyOperation(new TransactionOperation() {
+        txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
             @Override
             public void invoke(TransactionContext transactionContext) {
                 transactionContext.writeData(path, data);
@@ -345,12 +312,12 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
 
         checkModificationState();
 
-        LOG.debug("Tx {} merge {}", identifier, path);
+        LOG.debug("Tx {} merge {}", getIdentifier(), path);
 
         throttleOperation();
 
         TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
-        txFutureCallback.enqueueModifyOperation(new TransactionOperation() {
+        txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
             @Override
             public void invoke(TransactionContext transactionContext) {
                 transactionContext.mergeData(path, data);
@@ -363,12 +330,12 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
 
         checkModificationState();
 
-        LOG.debug("Tx {} delete {}", identifier, path);
+        LOG.debug("Tx {} delete {}", getIdentifier(), path);
 
         throttleOperation();
 
         TransactionFutureCallback txFutureCallback = getOrCreateTxFutureCallback(path);
-        txFutureCallback.enqueueModifyOperation(new TransactionOperation() {
+        txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
             @Override
             public void invoke(TransactionContext transactionContext) {
                 transactionContext.deleteData(path);
@@ -376,70 +343,76 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         });
     }
 
-    @Override
-    public DOMStoreThreePhaseCommitCohort ready() {
-
-        checkModificationState();
+    private boolean seal(final TransactionState newState) {
+        if (state == TransactionState.OPEN) {
+            state = newState;
+            return true;
+        } else {
+            return false;
+        }
+    }
 
-        throttleOperation(txFutureCallbackMap.size());
+    @Override
+    public AbstractThreePhaseCommitCohort ready() {
+        Preconditions.checkState(transactionType != TransactionType.READ_ONLY,
+                "Read-only transactions cannot be readied");
 
-        inReadyState = true;
+        final boolean success = seal(TransactionState.READY);
+        Preconditions.checkState(success, "Transaction %s is %s, it cannot be readied", getIdentifier(), state);
 
-        LOG.debug("Tx {} Readying {} transactions for commit", identifier,
+        LOG.debug("Tx {} Readying {} transactions for commit", getIdentifier(),
                     txFutureCallbackMap.size());
 
-        List<Future<ActorSelection>> cohortFutures = Lists.newArrayList();
+        if (txFutureCallbackMap.isEmpty()) {
+            TransactionRateLimitingCallback.adjustRateLimitForUnusedTransaction(actorContext);
+            return NoOpDOMStoreThreePhaseCommitCohort.INSTANCE;
+        }
+
+        throttleOperation(txFutureCallbackMap.size());
 
+        List<Future<ActorSelection>> cohortFutures = new ArrayList<>(txFutureCallbackMap.size());
         for(TransactionFutureCallback txFutureCallback : txFutureCallbackMap.values()) {
 
-            LOG.debug("Tx {} Readying transaction for shard {} chain {}", identifier,
+            LOG.debug("Tx {} Readying transaction for shard {} chain {}", getIdentifier(),
                         txFutureCallback.getShardName(), transactionChainId);
 
-            Future<ActorSelection> future = txFutureCallback.enqueueFutureOperation(new FutureOperation<ActorSelection>() {
-                @Override
-                public Future<ActorSelection> invoke(TransactionContext transactionContext) {
-                    return transactionContext.readyTransaction();
-                }
-            });
+            final TransactionContext transactionContext = txFutureCallback.getTransactionContext();
+            final Future<ActorSelection> future;
+            if (transactionContext != null) {
+                // avoid the creation of a promise and a TransactionOperation
+                future = transactionContext.readyTransaction();
+            } else {
+                final Promise<ActorSelection> promise = akka.dispatch.Futures.promise();
+                txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
+                    @Override
+                    public void invoke(TransactionContext transactionContext) {
+                        promise.completeWith(transactionContext.readyTransaction());
+                    }
+                });
+                future = promise.future();
+            }
 
             cohortFutures.add(future);
         }
 
-        onTransactionReady(cohortFutures);
-
         return new ThreePhaseCommitCohortProxy(actorContext, cohortFutures,
-                identifier.toString());
-    }
-
-    /**
-     * Method for derived classes to be notified when the transaction has been readied.
-     *
-     * @param cohortFutures the cohort Futures for each shard transaction.
-     */
-    protected void onTransactionReady(List<Future<ActorSelection>> cohortFutures) {
-    }
-
-    /**
-     * Method called to send a CreateTransaction message to a shard.
-     *
-     * @param shard the shard actor to send to
-     * @param serializedCreateMessage the serialized message to send
-     * @return the response Future
-     */
-    protected Future<Object> sendCreateTransaction(ActorSelection shard,
-            Object serializedCreateMessage) {
-        return actorContext.executeOperationAsync(shard, serializedCreateMessage);
-    }
-
-    @Override
-    public Object getIdentifier() {
-        return this.identifier;
+            getIdentifier().toString());
     }
 
     @Override
     public void close() {
+        if (!seal(TransactionState.CLOSED)) {
+            if (state == TransactionState.CLOSED) {
+                // Idempotent no-op as per AutoCloseable recommendation
+                return;
+            }
+
+            throw new IllegalStateException(String.format("Transaction %s is ready, it cannot be closed",
+                getIdentifier()));
+        }
+
         for (TransactionFutureCallback txFutureCallback : txFutureCallbackMap.values()) {
-            txFutureCallback.enqueueModifyOperation(new TransactionOperation() {
+            txFutureCallback.enqueueTransactionOperation(new TransactionOperation() {
                 @Override
                 public void invoke(TransactionContext transactionContext) {
                     transactionContext.closeTransaction();
@@ -449,7 +422,7 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
 
         txFutureCallbackMap.clear();
 
-        if(transactionType == TransactionType.READ_ONLY) {
+        if(remoteTransactionActorsMB != null) {
             remoteTransactionActors.clear();
             remoteTransactionActorsMB.set(true);
         }
@@ -459,14 +432,29 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         return ShardStrategyFactory.getStrategy(path).findShard(path);
     }
 
+    protected Future<ActorSelection> sendFindPrimaryShardAsync(String shardName) {
+        return actorContext.findPrimaryShardAsync(shardName);
+    }
+
+    final TransactionType getTransactionType() {
+        return transactionType;
+    }
+
+    final Semaphore getOperationLimiter() {
+        return operationLimiter;
+    }
+
     private TransactionFutureCallback getOrCreateTxFutureCallback(YangInstanceIdentifier path) {
         String shardName = shardNameFromIdentifier(path);
+        return getOrCreateTxFutureCallback(shardName);
+    }
+
+    private TransactionFutureCallback getOrCreateTxFutureCallback(String shardName) {
         TransactionFutureCallback txFutureCallback = txFutureCallbackMap.get(shardName);
         if(txFutureCallback == null) {
-            Future<ActorSelection> findPrimaryFuture = actorContext.findPrimaryShardAsync(shardName);
+            Future<ActorSelection> findPrimaryFuture = sendFindPrimaryShardAsync(shardName);
 
-            final TransactionFutureCallback newTxFutureCallback =
-                    new TransactionFutureCallback(shardName);
+            final TransactionFutureCallback newTxFutureCallback = new TransactionFutureCallback(this, shardName);
 
             txFutureCallback = newTxFutureCallback;
             txFutureCallbackMap.put(shardName, txFutureCallback);
@@ -475,18 +463,18 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
                 @Override
                 public void onComplete(Throwable failure, ActorSelection primaryShard) {
                     if(failure != null) {
-                        newTxFutureCallback.onComplete(failure, null);
+                        newTxFutureCallback.createTransactionContext(failure, null);
                     } else {
                         newTxFutureCallback.setPrimaryShard(primaryShard);
                     }
                 }
-            }, actorContext.getActorSystem().dispatcher());
+            }, actorContext.getClientDispatcher());
         }
 
         return txFutureCallback;
     }
 
-    public String getTransactionChainId() {
+    String getTransactionChainId() {
         return transactionChainId;
     }
 
@@ -494,680 +482,41 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         return actorContext;
     }
 
-    /**
-     * Interfaces for transaction operations to be invoked later.
-     */
-    private static interface TransactionOperation {
-        void invoke(TransactionContext transactionContext);
-    }
-
-    /**
-     * This interface returns a Guava Future
-     */
-    private static interface ReadOperation<T> {
-        CheckedFuture<T, ReadFailedException> invoke(TransactionContext transactionContext);
-    }
-
-    /**
-     * This interface returns a Scala Future
-     */
-    private static interface FutureOperation<T> {
-        Future<T> invoke(TransactionContext transactionContext);
-    }
-
-    /**
-     * Implements a Future OnComplete callback for a CreateTransaction message. This class handles
-     * retries, up to a limit, if the shard doesn't have a leader yet. This is done by scheduling a
-     * retry task after a short delay.
-     * <p>
-     * The end result from a completed CreateTransaction message is a TransactionContext that is
-     * used to perform transaction operations. Transaction operations that occur before the
-     * CreateTransaction completes are cache and executed once the CreateTransaction completes,
-     * successfully or not.
-     */
-    private class TransactionFutureCallback extends OnComplete<Object> {
-
-        /**
-         * The list of transaction operations to execute once the CreateTransaction completes.
-         */
-        @GuardedBy("txOperationsOnComplete")
-        private final List<TransactionOperation> txOperationsOnComplete = Lists.newArrayList();
-
-        /**
-         * The TransactionContext resulting from the CreateTransaction reply.
-         */
-        private volatile TransactionContext transactionContext;
-
-        /**
-         * The target primary shard.
-         */
-        private volatile ActorSelection primaryShard;
-
-        private volatile int createTxTries = (int) (actorContext.getDatastoreContext().
-                getShardLeaderElectionTimeout().duration().toMillis() /
-                CREATE_TX_TRY_INTERVAL.toMillis());
-
-        private final String shardName;
-
-        TransactionFutureCallback(String shardName) {
-            this.shardName = shardName;
-        }
-
-        String getShardName() {
-            return shardName;
-        }
-
-        TransactionContext getTransactionContext() {
-            return transactionContext;
-        }
-
-
-        /**
-         * Sets the target primary shard and initiates a CreateTransaction try.
-         */
-        void setPrimaryShard(ActorSelection primaryShard) {
-            LOG.debug("Tx {} Primary shard found - trying create transaction", identifier);
-
-            this.primaryShard = primaryShard;
-            tryCreateTransaction();
-        }
-
-        /**
-         * Adds a TransactionOperation to be executed after the CreateTransaction completes.
-         */
-        void addTxOperationOnComplete(TransactionOperation operation) {
-            synchronized(txOperationsOnComplete) {
-                if(transactionContext == null) {
-                    LOG.debug("Tx {} Adding operation on complete {}", identifier);
-
-                    txOperationsOnComplete.add(operation);
-                } else {
-                    operation.invoke(transactionContext);
-                }
-            }
-        }
-
-
-        <T> Future<T> enqueueFutureOperation(final FutureOperation<T> op) {
-
-            Future<T> future;
-
-            if (transactionContext != null) {
-                future = op.invoke(transactionContext);
-            } else {
-                // The shard Tx hasn't been created yet so add the Tx operation to the Tx Future
-                // callback to be executed after the Tx is created.
-                final Promise<T> promise = akka.dispatch.Futures.promise();
-                addTxOperationOnComplete(new TransactionOperation() {
-                    @Override
-                    public void invoke(TransactionContext transactionContext) {
-                        promise.completeWith(op.invoke(transactionContext));
-                    }
-                });
-
-                future = promise.future();
-            }
-
-            return future;
-        }
-
-        <T> CheckedFuture<T, ReadFailedException> enqueueReadOperation(final ReadOperation<T> op) {
-
-            CheckedFuture<T, ReadFailedException> future;
-
-            if (transactionContext != null) {
-                future = op.invoke(transactionContext);
-            } else {
-                // The shard Tx hasn't been created yet so add the Tx operation to the Tx Future
-                // callback to be executed after the Tx is created.
-                final SettableFuture<T> proxyFuture = SettableFuture.create();
-                addTxOperationOnComplete(new TransactionOperation() {
-                    @Override
-                    public void invoke(TransactionContext transactionContext) {
-                        Futures.addCallback(op.invoke(transactionContext), new FutureCallback<T>() {
-                            @Override
-                            public void onSuccess(T data) {
-                                proxyFuture.set(data);
-                            }
-
-                            @Override
-                            public void onFailure(Throwable t) {
-                                proxyFuture.setException(t);
-                            }
-                        });
-                    }
-                });
-
-                future = MappingCheckedFuture.create(proxyFuture, ReadFailedException.MAPPER);
-            }
-
-            return future;
-        }
-
-        void enqueueModifyOperation(final TransactionOperation op) {
-
-            if (transactionContext != null) {
-                op.invoke(transactionContext);
-            } else {
-                // The shard Tx hasn't been created yet so add the Tx operation to the Tx Future
-                // callback to be executed after the Tx is created.
-                addTxOperationOnComplete(op);
-            }
-        }
-
-        /**
-         * Performs a CreateTransaction try async.
-         */
-        private void tryCreateTransaction() {
-            Future<Object> createTxFuture = sendCreateTransaction(primaryShard,
-                    new CreateTransaction(identifier.toString(),
-                            TransactionProxy.this.transactionType.ordinal(),
-                            getTransactionChainId()).toSerializable());
-
-            createTxFuture.onComplete(this, actorContext.getActorSystem().dispatcher());
-        }
-
-        @Override
-        public void onComplete(Throwable failure, Object response) {
-            if(failure instanceof NoShardLeaderException) {
-                // There's no leader for the shard yet - schedule and try again, unless we're out
-                // of retries. Note: createTxTries is volatile as it may be written by different
-                // threads however not concurrently, therefore decrementing it non-atomically here
-                // is ok.
-                if(--createTxTries > 0) {
-                    LOG.debug("Tx {} Shard {} has no leader yet - scheduling create Tx retry",
-                            identifier, shardName);
-
-                    actorContext.getActorSystem().scheduler().scheduleOnce(CREATE_TX_TRY_INTERVAL,
-                            new Runnable() {
-                                @Override
-                                public void run() {
-                                    tryCreateTransaction();
-                                }
-                            }, actorContext.getActorSystem().dispatcher());
-                    return;
-                }
-            }
-
-            // Create the TransactionContext from the response or failure and execute delayed
-            // TransactionOperations. This entire section is done atomically (ie synchronized) with
-            // respect to #addTxOperationOnComplete to handle timing issues and ensure no
-            // TransactionOperation is missed and that they are processed in the order they occurred.
-            synchronized(txOperationsOnComplete) {
-                // Store the new TransactionContext locally until we've completed invoking the
-                // TransactionOperations. This avoids thread timing issues which could cause
-                // out-of-order TransactionOperations. Eg, on a modification operation, if the
-                // TransactionContext is non-null, then we directly call the TransactionContext.
-                // However, at the same time, the code may be executing the cached
-                // TransactionOperations. So to avoid thus timing, we don't publish the
-                // TransactionContext until after we've executed all cached TransactionOperations.
-                TransactionContext localTransactionContext;
-                if(failure != null) {
-                    LOG.debug("Tx {} Creating NoOpTransaction because of error: {}", identifier,
-                            failure.getMessage());
-
-                    localTransactionContext = new NoOpTransactionContext(failure, identifier, operationLimiter);
-                } else if (response.getClass().equals(CreateTransactionReply.SERIALIZABLE_CLASS)) {
-                    localTransactionContext = createValidTransactionContext(
-                            CreateTransactionReply.fromSerializable(response));
-                } else {
-                    IllegalArgumentException exception = new IllegalArgumentException(String.format(
-                        "Invalid reply type %s for CreateTransaction", response.getClass()));
-
-                    localTransactionContext = new NoOpTransactionContext(exception, identifier, operationLimiter);
-                }
-
-                for(TransactionOperation oper: txOperationsOnComplete) {
-                    oper.invoke(localTransactionContext);
-                }
-
-                txOperationsOnComplete.clear();
-
-                // We're done invoking the TransactionOperations so we can now publish the
-                // TransactionContext.
-                transactionContext = localTransactionContext;
-            }
-        }
-
-        private TransactionContext createValidTransactionContext(CreateTransactionReply reply) {
-            String transactionPath = reply.getTransactionPath();
-
-            LOG.debug("Tx {} Received transaction actor path {}", identifier, transactionPath);
-
-            ActorSelection transactionActor = actorContext.actorSelection(transactionPath);
-
-            if (transactionType == TransactionType.READ_ONLY) {
-                // Add the actor to the remoteTransactionActors list for access by the
-                // cleanup PhantonReference.
-                remoteTransactionActors.add(transactionActor);
-
-                // Write to the memory barrier volatile to publish the above update to the
-                // remoteTransactionActors list for thread visibility.
-                remoteTransactionActorsMB.set(true);
-            }
-
-            // TxActor is always created where the leader of the shard is.
-            // Check if TxActor is created in the same node
-            boolean isTxActorLocal = actorContext.isPathLocal(transactionPath);
-
-            return new TransactionContextImpl(transactionPath, transactionActor, identifier,
-                actorContext, schemaContext, isTxActorLocal, reply.getVersion(), operationCompleter);
-        }
-    }
-
-    private interface TransactionContext {
-        void closeTransaction();
-
-        Future<ActorSelection> readyTransaction();
-
-        void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
-
-        void deleteData(YangInstanceIdentifier path);
-
-        void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
-
-        CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
-                final YangInstanceIdentifier path);
-
-        CheckedFuture<Boolean, ReadFailedException> dataExists(YangInstanceIdentifier path);
-
-        List<Future<Object>> getRecordedOperationFutures();
-    }
-
-    private static abstract class AbstractTransactionContext implements TransactionContext {
-
-        protected final TransactionIdentifier identifier;
-        protected final List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
-
-        AbstractTransactionContext(TransactionIdentifier identifier) {
-            this.identifier = identifier;
-        }
-
-        @Override
-        public List<Future<Object>> getRecordedOperationFutures() {
-            return recordedOperationFutures;
-        }
-    }
-
-    private static class TransactionContextImpl extends AbstractTransactionContext {
-        private final Logger LOG = LoggerFactory.getLogger(TransactionContextImpl.class);
-
-        private final ActorContext actorContext;
-        private final String transactionPath;
-        private final ActorSelection actor;
-        private final boolean isTxActorLocal;
-        private final short remoteTransactionVersion;
-        private final OperationCompleter operationCompleter;
-
-
-        private TransactionContextImpl(String transactionPath, ActorSelection actor, TransactionIdentifier identifier,
-                ActorContext actorContext, SchemaContext schemaContext,
-                boolean isTxActorLocal, short remoteTransactionVersion, OperationCompleter operationCompleter) {
-            super(identifier);
-            this.transactionPath = transactionPath;
-            this.actor = actor;
-            this.actorContext = actorContext;
-            this.isTxActorLocal = isTxActorLocal;
-            this.remoteTransactionVersion = remoteTransactionVersion;
-            this.operationCompleter = operationCompleter;
-        }
-
-        private Future<Object> completeOperation(Future<Object> operationFuture){
-            operationFuture.onComplete(this.operationCompleter, actorContext.getActorSystem().dispatcher());
-            return operationFuture;
-        }
-
-
-        private ActorSelection getActor() {
-            return actor;
-        }
-
-        private Future<Object> executeOperationAsync(SerializableMessage msg) {
-            return completeOperation(actorContext.executeOperationAsync(getActor(), isTxActorLocal ? msg : msg.toSerializable()));
-        }
-
-        private Future<Object> executeOperationAsync(VersionedSerializableMessage msg) {
-            return completeOperation(actorContext.executeOperationAsync(getActor(), isTxActorLocal ? msg :
-                    msg.toSerializable(remoteTransactionVersion)));
-        }
-
-        @Override
-        public void closeTransaction() {
-            LOG.debug("Tx {} closeTransaction called", identifier);
-
-            actorContext.sendOperationAsync(getActor(), CloseTransaction.INSTANCE.toSerializable());
-        }
-
-        @Override
-        public Future<ActorSelection> readyTransaction() {
-            LOG.debug("Tx {} readyTransaction called with {} previous recorded operations pending",
-                    identifier, recordedOperationFutures.size());
-
-            // Send the ReadyTransaction message to the Tx actor.
-
-            final Future<Object> replyFuture = executeOperationAsync(ReadyTransaction.INSTANCE);
-
-            // Combine all the previously recorded put/merge/delete operation reply Futures and the
-            // ReadyTransactionReply Future into one Future. If any one fails then the combined
-            // Future will fail. We need all prior operations and the ready operation to succeed
-            // in order to attempt commit.
-
-            List<Future<Object>> futureList =
-                    Lists.newArrayListWithCapacity(recordedOperationFutures.size() + 1);
-            futureList.addAll(recordedOperationFutures);
-            futureList.add(replyFuture);
-
-            Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(futureList,
-                    actorContext.getActorSystem().dispatcher());
-
-            // Transform the combined Future into a Future that returns the cohort actor path from
-            // the ReadyTransactionReply. That's the end result of the ready operation.
-
-            return combinedFutures.transform(new Mapper<Iterable<Object>, ActorSelection>() {
-                @Override
-                public ActorSelection checkedApply(Iterable<Object> notUsed) {
-                    LOG.debug("Tx {} readyTransaction: pending recorded operations succeeded",
-                            identifier);
-
-                    // At this point all the Futures succeeded and we need to extract the cohort
-                    // actor path from the ReadyTransactionReply. For the recorded operations, they
-                    // don't return any data so we're only interested that they completed
-                    // successfully. We could be paranoid and verify the correct reply types but
-                    // that really should never happen so it's not worth the overhead of
-                    // de-serializing each reply.
-
-                    // Note the Future get call here won't block as it's complete.
-                    Object serializedReadyReply = replyFuture.value().get().get();
-                    if (serializedReadyReply instanceof ReadyTransactionReply) {
-                        return actorContext.actorSelection(((ReadyTransactionReply)serializedReadyReply).getCohortPath());
-
-                    } else if(serializedReadyReply.getClass().equals(ReadyTransactionReply.SERIALIZABLE_CLASS)) {
-                        ReadyTransactionReply reply = ReadyTransactionReply.fromSerializable(serializedReadyReply);
-                        String cohortPath = reply.getCohortPath();
-
-                        // In Helium we used to return the local path of the actor which represented
-                        // a remote ThreePhaseCommitCohort. The local path would then be converted to
-                        // a remote path using this resolvePath method. To maintain compatibility with
-                        // a Helium node we need to continue to do this conversion.
-                        // At some point in the future when upgrades from Helium are not supported
-                        // we could remove this code to resolvePath and just use the cohortPath as the
-                        // resolved cohortPath
-                        if(TransactionContextImpl.this.remoteTransactionVersion <
-                                DataStoreVersions.HELIUM_1_VERSION) {
-                            cohortPath = actorContext.resolvePath(transactionPath, cohortPath);
-                        }
-
-                        return actorContext.actorSelection(cohortPath);
-
-                    } else {
-                        // Throwing an exception here will fail the Future.
-                        throw new IllegalArgumentException(String.format("Invalid reply type {}",
-                                serializedReadyReply.getClass()));
-                    }
-                }
-            }, SAME_FAILURE_TRANSFORMER, actorContext.getActorSystem().dispatcher());
-        }
-
-        @Override
-        public void deleteData(YangInstanceIdentifier path) {
-            LOG.debug("Tx {} deleteData called path = {}", identifier, path);
-
-            recordedOperationFutures.add(executeOperationAsync(new DeleteData(path)));
-        }
-
-        @Override
-        public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
-            LOG.debug("Tx {} mergeData called path = {}", identifier, path);
-
-            recordedOperationFutures.add(executeOperationAsync(new MergeData(path, data)));
-        }
-
-        @Override
-        public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
-            LOG.debug("Tx {} writeData called path = {}", identifier, path);
-
-            recordedOperationFutures.add(executeOperationAsync(new WriteData(path, data)));
-        }
-
-        @Override
-        public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
-                final YangInstanceIdentifier path) {
-
-            LOG.debug("Tx {} readData called path = {}", identifier, path);
-
-            final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture = SettableFuture.create();
-
-            // If there were any previous recorded put/merge/delete operation reply Futures then we
-            // must wait for them to successfully complete. This is necessary to honor the read
-            // uncommitted semantics of the public API contract. If any one fails then fail the read.
-
-            if(recordedOperationFutures.isEmpty()) {
-                finishReadData(path, returnFuture);
-            } else {
-                LOG.debug("Tx {} readData: verifying {} previous recorded operations",
-                        identifier, recordedOperationFutures.size());
-
-                // Note: we make a copy of recordedOperationFutures to be on the safe side in case
-                // Futures#sequence accesses the passed List on a different thread, as
-                // recordedOperationFutures is not synchronized.
+    TransactionContext createValidTransactionContext(ActorSelection transactionActor,
+            String transactionPath, short remoteTransactionVersion) {
 
-                Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
-                        Lists.newArrayList(recordedOperationFutures),
-                        actorContext.getActorSystem().dispatcher());
+        if (transactionType == TransactionType.READ_ONLY) {
+            // Read-only Tx's aren't explicitly closed by the client so we create a PhantomReference
+            // to close the remote Tx's when this instance is no longer in use and is garbage
+            // collected.
 
-                OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
-                    @Override
-                    public void onComplete(Throwable failure, Iterable<Object> notUsed)
-                            throws Throwable {
-                        if(failure != null) {
-                            LOG.debug("Tx {} readData: a recorded operation failed: {}",
-                                    identifier, failure);
-                            returnFuture.setException(new ReadFailedException(
-                                    "The read could not be performed because a previous put, merge,"
-                                    + "or delete operation failed", failure));
-                        } else {
-                            finishReadData(path, returnFuture);
-                        }
-                    }
-                };
+            if(remoteTransactionActorsMB == null) {
+                remoteTransactionActors = Lists.newArrayList();
+                remoteTransactionActorsMB = new AtomicBoolean();
 
-                combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
+                TransactionProxyCleanupPhantomReference.track(TransactionProxy.this);
             }
 
-            return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
-        }
-
-        private void finishReadData(final YangInstanceIdentifier path,
-                final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture) {
+            // Add the actor to the remoteTransactionActors list for access by the
+            // cleanup PhantonReference.
+            remoteTransactionActors.add(transactionActor);
 
-            LOG.debug("Tx {} finishReadData called path = {}", identifier, path);
-
-            OnComplete<Object> onComplete = new OnComplete<Object>() {
-                @Override
-                public void onComplete(Throwable failure, Object readResponse) throws Throwable {
-                    if(failure != null) {
-                        LOG.debug("Tx {} read operation failed: {}", identifier, failure);
-                        returnFuture.setException(new ReadFailedException(
-                                "Error reading data for path " + path, failure));
-
-                    } else {
-                        LOG.debug("Tx {} read operation succeeded", identifier, failure);
-
-                        if (readResponse instanceof ReadDataReply) {
-                            ReadDataReply reply = (ReadDataReply) readResponse;
-                            returnFuture.set(Optional.<NormalizedNode<?, ?>>fromNullable(reply.getNormalizedNode()));
-
-                        } else if (ReadDataReply.isSerializedType(readResponse)) {
-                            ReadDataReply reply = ReadDataReply.fromSerializable(readResponse);
-                            returnFuture.set(Optional.<NormalizedNode<?, ?>>fromNullable(reply.getNormalizedNode()));
-
-                        } else {
-                            returnFuture.setException(new ReadFailedException(
-                                "Invalid response reading data for path " + path));
-                        }
-                    }
-                }
-            };
-
-            Future<Object> readFuture = executeOperationAsync(new ReadData(path));
-
-            readFuture.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
-        }
-
-        @Override
-        public CheckedFuture<Boolean, ReadFailedException> dataExists(
-                final YangInstanceIdentifier path) {
-
-            LOG.debug("Tx {} dataExists called path = {}", identifier, path);
-
-            final SettableFuture<Boolean> returnFuture = SettableFuture.create();
-
-            // If there were any previous recorded put/merge/delete operation reply Futures then we
-            // must wait for them to successfully complete. This is necessary to honor the read
-            // uncommitted semantics of the public API contract. If any one fails then fail this
-            // request.
-
-            if(recordedOperationFutures.isEmpty()) {
-                finishDataExists(path, returnFuture);
-            } else {
-                LOG.debug("Tx {} dataExists: verifying {} previous recorded operations",
-                        identifier, recordedOperationFutures.size());
-
-                // Note: we make a copy of recordedOperationFutures to be on the safe side in case
-                // Futures#sequence accesses the passed List on a different thread, as
-                // recordedOperationFutures is not synchronized.
-
-                Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
-                        Lists.newArrayList(recordedOperationFutures),
-                        actorContext.getActorSystem().dispatcher());
-                OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
-                    @Override
-                    public void onComplete(Throwable failure, Iterable<Object> notUsed)
-                            throws Throwable {
-                        if(failure != null) {
-                            LOG.debug("Tx {} dataExists: a recorded operation failed: {}",
-                                    identifier, failure);
-                            returnFuture.setException(new ReadFailedException(
-                                    "The data exists could not be performed because a previous "
-                                    + "put, merge, or delete operation failed", failure));
-                        } else {
-                            finishDataExists(path, returnFuture);
-                        }
-                    }
-                };
-
-                combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
-            }
-
-            return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
-        }
-
-        private void finishDataExists(final YangInstanceIdentifier path,
-                final SettableFuture<Boolean> returnFuture) {
-
-            LOG.debug("Tx {} finishDataExists called path = {}", identifier, path);
-
-            OnComplete<Object> onComplete = new OnComplete<Object>() {
-                @Override
-                public void onComplete(Throwable failure, Object response) throws Throwable {
-                    if(failure != null) {
-                        LOG.debug("Tx {} dataExists operation failed: {}", identifier, failure);
-                        returnFuture.setException(new ReadFailedException(
-                                "Error checking data exists for path " + path, failure));
-                    } else {
-                        LOG.debug("Tx {} dataExists operation succeeded", identifier, failure);
-
-                        if (response instanceof DataExistsReply) {
-                            returnFuture.set(Boolean.valueOf(((DataExistsReply) response).exists()));
-
-                        } else if (response.getClass().equals(DataExistsReply.SERIALIZABLE_CLASS)) {
-                            returnFuture.set(Boolean.valueOf(DataExistsReply.fromSerializable(response).exists()));
-
-                        } else {
-                            returnFuture.setException(new ReadFailedException(
-                                    "Invalid response checking exists for path " + path));
-                        }
-                    }
-                }
-            };
-
-            Future<Object> future = executeOperationAsync(new DataExists(path));
-
-            future.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
-        }
-    }
-
-    private static class NoOpTransactionContext extends AbstractTransactionContext {
-
-        private final Logger LOG = LoggerFactory.getLogger(NoOpTransactionContext.class);
-
-        private final Throwable failure;
-        private final Semaphore operationLimiter;
-
-        public NoOpTransactionContext(Throwable failure, TransactionIdentifier identifier, Semaphore operationLimiter){
-            super(identifier);
-            this.failure = failure;
-            this.operationLimiter = operationLimiter;
-        }
-
-        @Override
-        public void closeTransaction() {
-            LOG.debug("NoOpTransactionContext {} closeTransaction called", identifier);
-        }
-
-        @Override
-        public Future<ActorSelection> readyTransaction() {
-            LOG.debug("Tx {} readyTransaction called", identifier);
-            operationLimiter.release();
-            return akka.dispatch.Futures.failed(failure);
-        }
-
-        @Override
-        public void deleteData(YangInstanceIdentifier path) {
-            LOG.debug("Tx {} deleteData called path = {}", identifier, path);
-            operationLimiter.release();
-        }
-
-        @Override
-        public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
-            LOG.debug("Tx {} mergeData called path = {}", identifier, path);
-            operationLimiter.release();
-        }
-
-        @Override
-        public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
-            LOG.debug("Tx {} writeData called path = {}", identifier, path);
-            operationLimiter.release();
-        }
-
-        @Override
-        public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
-                YangInstanceIdentifier path) {
-            LOG.debug("Tx {} readData called path = {}", identifier, path);
-            operationLimiter.release();
-            return Futures.immediateFailedCheckedFuture(new ReadFailedException(
-                    "Error reading data for path " + path, failure));
-        }
-
-        @Override
-        public CheckedFuture<Boolean, ReadFailedException> dataExists(
-                YangInstanceIdentifier path) {
-            LOG.debug("Tx {} dataExists called path = {}", identifier, path);
-            operationLimiter.release();
-            return Futures.immediateFailedCheckedFuture(new ReadFailedException(
-                    "Error checking exists for path " + path, failure));
+            // Write to the memory barrier volatile to publish the above update to the
+            // remoteTransactionActors list for thread visibility.
+            remoteTransactionActorsMB.set(true);
         }
-    }
 
-    private static class OperationCompleter extends OnComplete<Object> {
-        private final Semaphore operationLimiter;
-        OperationCompleter(Semaphore operationLimiter){
-            this.operationLimiter = operationLimiter;
-        }
+        // TxActor is always created where the leader of the shard is.
+        // Check if TxActor is created in the same node
+        boolean isTxActorLocal = actorContext.isPathLocal(transactionPath);
 
-        @Override
-        public void onComplete(Throwable throwable, Object o){
-            this.operationLimiter.release();
+        if(remoteTransactionVersion < DataStoreVersions.LITHIUM_VERSION) {
+            return new PreLithiumTransactionContextImpl(transactionPath, transactionActor, getIdentifier(),
+                    transactionChainId, actorContext, schemaContext, isTxActorLocal, remoteTransactionVersion,
+                    operationCompleter);
+        } else {
+            return new TransactionContextImpl(transactionActor, getIdentifier(), transactionChainId,
+                    actorContext, schemaContext, isTxActorLocal, remoteTransactionVersion, operationCompleter);
         }
     }
 }