WIP: Revamped transaction API. Introduces a transaction context for running bloc…

…ks of code that can be committed
atomically.

Change-Id: I6ba21050a2644a42f3c073fa04ff776ef2c5ff4c

@@ -17,7 +17,6 @@
 package org.onosproject.store.service;
 package org.onosproject.store.service;
 
 
 import java.util.Collection;
 import java.util.Collection;
-import java.util.List;
 import java.util.Set;
 import java.util.Set;
 import java.util.Map.Entry;
 import java.util.Map.Entry;
 
 
@@ -37,13 +36,6 @@ import java.util.Map.Entry;
  * concurrency by allowing conditional updates that take into consideration
  * concurrency by allowing conditional updates that take into consideration
  * the version or value that was previously read.
  * the version or value that was previously read.
  * </p><p>
  * </p><p>
- * The map also supports atomic batch updates (transactions). One can provide a list
- * of updates to be applied atomically if and only if all the operations are guaranteed
- * to succeed i.e. all their preconditions are met. For example, the precondition
- * for a putIfAbsent API call is absence of a mapping for the key. Similarly, the
- * precondition for a conditional replace operation is the presence of an expected
- * version or value
- * </p><p>
  * This map does not allow null values. All methods can throw a ConsistentMapException
  * This map does not allow null values. All methods can throw a ConsistentMapException
  * (which extends RuntimeException) to indicate failures.
  * (which extends RuntimeException) to indicate failures.
  *
  *
@@ -202,15 +194,4 @@ public interface ConsistentMap<K, V> {
      * @return true if the value was replaced
      * @return true if the value was replaced
      */
      */
     boolean replace(K key, long oldVersion, V newValue);
     boolean replace(K key, long oldVersion, V newValue);
-
-    /**
-     * Atomically apply the specified list of updates to the map.
-     * If any of the updates cannot be applied due to a precondition
-     * violation, none of the updates will be applied and the state of
-     * the map remains unaltered.
-     *
-     * @param updates list of updates to apply atomically.
-     * @return true if the map was updated.
-     */
-    boolean batchUpdate(List<UpdateOperation<K, V>> updates);
 }
 }

@@ -39,5 +39,9 @@ public interface StorageService {
      */
      */
     <K, V> ConsistentMap<K , V> createConsistentMap(String name, Serializer serializer);
     <K, V> ConsistentMap<K , V> createConsistentMap(String name, Serializer serializer);
 
 
-    // TODO: add API for creating Eventually Consistent Map.
+    /**
+     * Creates a new transaction context.
+     * @return transaction context
+     */
+    TransactionContext createTransactionContext();
 }
 }
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.service;
+
+/**
+ * Provides a context for transactional operations.
+ * <p>
+ * A transaction context provides a boundary within which transactions
+ * are run. It also is a place where all modifications made within a transaction
+ * are cached until the point when the transaction commits or aborts. It thus ensures
+ * isolation of work happening with in the transaction boundary.
+ * <p>
+ * A transaction context is a vehicle for grouping operations into a unit with the
+ * properties of atomicity, isolation, and durability. Transactions also provide the
+ * ability to maintain an application's invariants or integrity constraints,
+ * supporting the property of consistency. Together these properties are known as ACID.
+ */
+public interface TransactionContext {
+
+    /**
+     * Returns if this transaction context is open.
+     * @return true if open, false otherwise.
+     */
+    boolean isOpen();
+
+    /**
+     * Starts a new transaction.
+     */
+    void begin();
+
+    /**
+     * Commits a transaction that was previously started thereby making its changes permanent
+     * and externally visible.
+     * @throws TransactionException if transaction fails to commit.
+     */
+    void commit();
+
+    /**
+     * Rolls back the current transaction, discarding all its changes.
+     */
+    void rollback();
+
+    /**
+     * Creates a new transactional map.
+     * @param mapName name of the transactional map.
+     * @param serializer serializer to use for encoding/decoding keys and vaulues.
+     * @return new Transactional Map.
+     */
+    <K, V> TransactionalMap<K, V> createTransactionalMap(String mapName, Serializer serializer);
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.service;
+
+/**
+ * Top level exception for Transaction failures.
+ */
+@SuppressWarnings("serial")
+public class TransactionException extends RuntimeException {
+    public TransactionException() {
+    }
+
+    public TransactionException(Throwable t) {
+        super(t);
+    }
+
+    /**
+     * Transaction timeout.
+     */
+    public static class Timeout extends TransactionException {
+    }
+
+    /**
+     * Transaction interrupted.
+     */
+    public static class Interrupted extends TransactionException {
+    }
+
+    /**
+     * Transaction failure due to optimistic concurrency failure.
+     */
+    public static class OptimisticConcurrencyFailure extends TransactionException {
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.service;
+
+import java.util.Collection;
+import java.util.Set;
+import java.util.Map.Entry;
+
+/**
+ * Transactional Map data structure.
+ * <p>
+ * A TransactionalMap is created by invoking {@link TransactionContext#createTransactionalMap createTransactionalMap}
+ * method. All operations performed on this map with in a transaction boundary are invisible externally
+ * until the point when the transaction commits. A commit usually succeeds in the absence of conflicts.
+ *
+ * @param <K> type of key.
+ * @param <V> type of value.
+ */
+public interface TransactionalMap<K, V> {
+
+    /**
+     * Returns the number of entries in the map.
+     *
+     * @return map size.
+     */
+    int size();
+
+    /**
+     * Returns true if the map is empty.
+     *
+     * @return true if map has no entries, false otherwise.
+     */
+    boolean isEmpty();
+
+    /**
+     * Returns true if this map contains a mapping for the specified key.
+     *
+     * @param key key
+     * @return true if map contains key, false otherwise.
+     */
+    boolean containsKey(K key);
+
+    /**
+     * Returns true if this map contains the specified value.
+     *
+     * @param value value
+     * @return true if map contains value, false otherwise.
+     */
+    boolean containsValue(V value);
+
+    /**
+     * Returns the value to which the specified key is mapped, or null if this
+     * map contains no mapping for the key.
+     *
+     * @param key the key whose associated value is to be returned
+     * @return the value to which the specified key is mapped, or null if
+     * this map contains no mapping for the key
+     */
+    V get(K key);
+
+    /**
+     * Associates the specified value with the specified key in this map (optional operation).
+     * If the map previously contained a mapping for the key, the old value is replaced by the
+     * specified value.
+     *
+     * @param key key with which the specified value is to be associated
+     * @param value value to be associated with the specified key
+     * @return the previous value associated with key, or null if there was
+     * no mapping for key.
+     */
+    V put(K key, V value);
+
+    /**
+     * Removes the mapping for a key from this map if it is present (optional operation).
+     *
+     * @param key key whose value is to be removed from the map
+     * @return the value to which this map previously associated the key,
+     * or null if the map contained no mapping for the key.
+     */
+    V remove(K key);
+
+    /**
+     * Removes all of the mappings from this map (optional operation).
+     * The map will be empty after this call returns.
+     */
+    void clear();
+
+    /**
+     * Returns a Set view of the keys contained in this map.
+     * This method differs from the behavior of java.util.Map.keySet() in that
+     * what is returned is a unmodifiable snapshot view of the keys in the ConsistentMap.
+     * Attempts to modify the returned set, whether direct or via its iterator,
+     * result in an UnsupportedOperationException.
+     *
+     * @return a set of the keys contained in this map
+     */
+    Set<K> keySet();
+
+    /**
+     * Returns the collection of values contained in this map.
+     * This method differs from the behavior of java.util.Map.values() in that
+     * what is returned is a unmodifiable snapshot view of the values in the ConsistentMap.
+     * Attempts to modify the returned collection, whether direct or via its iterator,
+     * result in an UnsupportedOperationException.
+     *
+     * @return a collection of the values contained in this map
+     */
+    Collection<V> values();
+
+    /**
+     * Returns the set of entries contained in this map.
+     * This method differs from the behavior of java.util.Map.entrySet() in that
+     * what is returned is a unmodifiable snapshot view of the entries in the ConsistentMap.
+     * Attempts to modify the returned set, whether direct or via its iterator,
+     * result in an UnsupportedOperationException.
+     *
+     * @return set of entries contained in this map.
+     */
+    Set<Entry<K, V>> entrySet();
+
+    /**
+     * If the specified key is not already associated with a value
+     * associates it with the given value and returns null, else returns the current value.
+     *
+     * @param key key with which the specified value is to be associated
+     * @param value value to be associated with the specified key
+     * @return the previous value associated with the specified key or null
+     * if key does not already mapped to a value.
+     */
+    V putIfAbsent(K key, V value);
+
+    /**
+     * Removes the entry for the specified key only if it is currently
+     * mapped to the specified value.
+     *
+     * @param key key with which the specified value is associated
+     * @param value value expected to be associated with the specified key
+     * @return true if the value was removed
+     */
+    boolean remove(K key, V value);
+
+    /**
+     * Replaces the entry for the specified key only if currently mapped
+     * to the specified value.
+     *
+     * @param key key with which the specified value is associated
+     * @param oldValue value expected to be associated with the specified key
+     * @param newValue value to be associated with the specified key
+     * @return true if the value was replaced
+     */
+    boolean replace(K key, V oldValue, V newValue);
+}
\ No newline at end of file

@@ -20,7 +20,6 @@ import static com.google.common.base.Preconditions.*;
 
 
 import java.util.Collection;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Collections;
-import java.util.List;
 import java.util.Map;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Map.Entry;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletableFuture;
@@ -35,7 +34,6 @@ import org.onlab.util.HexString;
 import org.onosproject.store.service.ConsistentMap;
 import org.onosproject.store.service.ConsistentMap;
 import org.onosproject.store.service.ConsistentMapException;
 import org.onosproject.store.service.ConsistentMapException;
 import org.onosproject.store.service.Serializer;
 import org.onosproject.store.service.Serializer;
-import org.onosproject.store.service.UpdateOperation;
 import org.onosproject.store.service.Versioned;
 import org.onosproject.store.service.Versioned;
 
 
 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheBuilder;
@@ -73,7 +71,7 @@ public class ConsistentMapImpl<K, V> implements ConsistentMap<K, V> {
         return serializer.decode(HexString.fromHexString(key));
         return serializer.decode(HexString.fromHexString(key));
     }
     }
 
 
-    ConsistentMapImpl(String name,
+    public ConsistentMapImpl(String name,
             DatabaseProxy<String, byte[]> proxy,
             DatabaseProxy<String, byte[]> proxy,
             Serializer serializer) {
             Serializer serializer) {
         this.name = checkNotNull(name, "map name cannot be null");
         this.name = checkNotNull(name, "map name cannot be null");
@@ -196,15 +194,6 @@ public class ConsistentMapImpl<K, V> implements ConsistentMap<K, V> {
         return complete(proxy.replace(name, keyCache.getUnchecked(key), oldVersion, serializer.encode(newValue)));
         return complete(proxy.replace(name, keyCache.getUnchecked(key), oldVersion, serializer.encode(newValue)));
     }
     }
 
 
-    @Override
-    public boolean batchUpdate(List<UpdateOperation<K, V>> updates) {
-        checkNotNull(updates, "updates cannot be null");
-        return complete(proxy.atomicBatchUpdate(updates
-                .stream()
-                .map(this::toRawUpdateOperation)
-                .collect(Collectors.toList())));
-    }
-
     private static <T> T complete(CompletableFuture<T> future) {
     private static <T> T complete(CompletableFuture<T> future) {
         try {
         try {
             return future.get(OPERATION_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
             return future.get(OPERATION_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
@@ -225,31 +214,4 @@ public class ConsistentMapImpl<K, V> implements ConsistentMap<K, V> {
                         serializer.decode(e.getValue().value()),
                         serializer.decode(e.getValue().value()),
                         e.getValue().version()));
                         e.getValue().version()));
     }
     }
-
-    private UpdateOperation<String, byte[]> toRawUpdateOperation(UpdateOperation<K, V> update) {
-
-        checkArgument(name.equals(update.tableName()), "Unexpected table name");
-
-        UpdateOperation.Builder<String, byte[]> rawUpdate = UpdateOperation.<String, byte[]>newBuilder();
-
-        rawUpdate = rawUpdate.withKey(keyCache.getUnchecked(update.key()))
-            .withCurrentVersion(update.currentVersion())
-            .withType(update.type());
-
-        rawUpdate = rawUpdate.withTableName(update.tableName());
-
-        if (update.value() != null) {
-            rawUpdate = rawUpdate.withValue(serializer.encode(update.value()));
-        } else {
-            checkState(update.type() == UpdateOperation.Type.REMOVE
-                    || update.type() == UpdateOperation.Type.REMOVE_IF_VERSION_MATCH,
-                    ERROR_NULL_VALUE);
-        }
-
-        if (update.currentValue() != null) {
-            rawUpdate = rawUpdate.withCurrentValue(serializer.encode(update.currentValue()));
-        }
-
-        return rawUpdate.build();
-    }
 }
 }
\ No newline at end of file

@@ -41,6 +41,7 @@ import org.onosproject.cluster.DefaultControllerNode;
 import org.onosproject.store.service.ConsistentMap;
 import org.onosproject.store.service.ConsistentMap;
 import org.onosproject.store.service.Serializer;
 import org.onosproject.store.service.Serializer;
 import org.onosproject.store.service.StorageService;
 import org.onosproject.store.service.StorageService;
+import org.onosproject.store.service.TransactionContext;
 import org.slf4j.Logger;
 import org.slf4j.Logger;
 
 
 import com.google.common.collect.Sets;
 import com.google.common.collect.Sets;
@@ -154,4 +155,9 @@ public class DatabaseManager implements StorageService {
     public <K, V> ConsistentMap<K , V> createConsistentMap(String name, Serializer serializer) {
     public <K, V> ConsistentMap<K , V> createConsistentMap(String name, Serializer serializer) {
         return new ConsistentMapImpl<K, V>(name, partitionedDatabase, serializer);
         return new ConsistentMapImpl<K, V>(name, partitionedDatabase, serializer);
     }
     }
+
+    @Override
+    public TransactionContext createTransactionContext() {
+        return new DefaultTransactionContext(partitionedDatabase);
+    }
 }
 }
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.consistent.impl;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import static com.google.common.base.Preconditions.*;
+
+import org.onosproject.store.service.ConsistentMap;
+import org.onosproject.store.service.Serializer;
+import org.onosproject.store.service.TransactionContext;
+import org.onosproject.store.service.TransactionException;
+import org.onosproject.store.service.TransactionalMap;
+import org.onosproject.store.service.UpdateOperation;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+
+/**
+ * Default TransactionContext implementation.
+ */
+public class DefaultTransactionContext implements TransactionContext {
+
+    private final Map<String, DefaultTransactionalMap> txMaps = Maps.newHashMap();
+    private boolean isOpen = false;
+    DatabaseProxy<String, byte[]> databaseProxy;
+    private static final String TX_NOT_OPEN_ERROR = "Transaction is not open";
+    private static final int TRANSACTION_TIMEOUT_MILLIS = 2000;
+
+    DefaultTransactionContext(DatabaseProxy<String, byte[]> proxy) {
+        this.databaseProxy = proxy;
+    }
+
+    @Override
+    public void begin() {
+        isOpen = true;
+    }
+
+    @Override
+    public <K, V> TransactionalMap<K, V> createTransactionalMap(String mapName,
+            Serializer serializer) {
+        checkNotNull(mapName, "map name is null");
+        checkNotNull(serializer, "serializer is null");
+        checkState(isOpen, TX_NOT_OPEN_ERROR);
+        if (!txMaps.containsKey(mapName)) {
+            ConsistentMap<K, V> backingMap = new ConsistentMapImpl<>(mapName, databaseProxy, serializer);
+            DefaultTransactionalMap<K, V> txMap = new DefaultTransactionalMap<>(mapName, backingMap, this, serializer);
+            txMaps.put(mapName, txMap);
+        }
+        return txMaps.get(mapName);
+    }
+
+    @Override
+    public void commit() {
+        checkState(isOpen, TX_NOT_OPEN_ERROR);
+        List<UpdateOperation<String, byte[]>> allUpdates =
+                Lists.newLinkedList();
+        try {
+            txMaps.values()
+                .stream()
+                .forEach(m -> {
+                    allUpdates.addAll(m.prepareDatabaseUpdates());
+                });
+
+            if (!complete(databaseProxy.atomicBatchUpdate(allUpdates))) {
+                throw new TransactionException.OptimisticConcurrencyFailure();
+            }
+        } finally {
+            isOpen = false;
+        }
+    }
+
+    @Override
+    public void rollback() {
+        checkState(isOpen, TX_NOT_OPEN_ERROR);
+        txMaps.values()
+        .stream()
+        .forEach(m -> m.rollback());
+    }
+
+    @Override
+    public boolean isOpen() {
+        return false;
+    }
+
+    private static <T> T complete(CompletableFuture<T> future) {
+        try {
+            return future.get(TRANSACTION_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new TransactionException.Interrupted();
+        } catch (TimeoutException e) {
+            throw new TransactionException.Timeout();
+        } catch (ExecutionException e) {
+            throw new TransactionException(e.getCause());
+        }
+    }
+}

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.store.consistent.impl;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.stream.Collectors;
+import java.util.Set;
+
+import org.onlab.util.HexString;
+import org.onosproject.store.service.ConsistentMap;
+import org.onosproject.store.service.Serializer;
+import org.onosproject.store.service.TransactionContext;
+import org.onosproject.store.service.TransactionalMap;
+import org.onosproject.store.service.UpdateOperation;
+import org.onosproject.store.service.Versioned;
+
+import static com.google.common.base.Preconditions.*;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+
+/**
+ * Default Transactional Map implementation that provides a repeatable reads
+ * transaction isolation level.
+ *
+ * @param <K> key type
+ * @param <V> value type.
+ */
+public class DefaultTransactionalMap<K, V> implements TransactionalMap<K, V> {
+
+    private final TransactionContext txContext;
+    private static final String TX_CLOSED_ERROR = "Transaction is closed";
+    private final ConsistentMap<K, V> backingMap;
+    private final String name;
+    private final Serializer serializer;
+    private final Map<K, Versioned<V>> readCache = Maps.newConcurrentMap();
+    private final Map<K, V> writeCache = Maps.newConcurrentMap();
+    private final Set<K> deleteSet = Sets.newConcurrentHashSet();
+
+    public DefaultTransactionalMap(
+            String name,
+            ConsistentMap<K, V> backingMap,
+            TransactionContext txContext,
+            Serializer serializer) {
+        this.name = name;
+        this.backingMap = backingMap;
+        this.txContext = txContext;
+        this.serializer = serializer;
+    }
+
+    @Override
+    public V get(K key) {
+        checkState(txContext.isOpen(), TX_CLOSED_ERROR);
+        if (deleteSet.contains(key)) {
+            return null;
+        } else if (writeCache.containsKey(key)) {
+            return writeCache.get(key);
+        } else {
+            if (!readCache.containsKey(key)) {
+                readCache.put(key, backingMap.get(key));
+            }
+            Versioned<V> v = readCache.get(key);
+            return v != null ? v.value() : null;
+        }
+    }
+
+    @Override
+    public V put(K key, V value) {
+        checkState(txContext.isOpen(), TX_CLOSED_ERROR);
+        Versioned<V> original = readCache.get(key);
+        V recentUpdate = writeCache.put(key, value);
+        deleteSet.remove(key);
+        return recentUpdate == null ? (original != null ? original.value() : null) : recentUpdate;
+    }
+
+    @Override
+    public V remove(K key) {
+        checkState(txContext.isOpen(), TX_CLOSED_ERROR);
+        Versioned<V> original = readCache.get(key);
+        V recentUpdate = writeCache.remove(key);
+        deleteSet.add(key);
+        return recentUpdate == null ? (original != null ? original.value() : null) : recentUpdate;
+    }
+
+    @Override
+    public boolean remove(K key, V value) {
+        V currentValue = get(key);
+        if (value.equals(currentValue)) {
+            remove(key);
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public boolean replace(K key, V oldValue, V newValue) {
+        V currentValue = get(key);
+        if (oldValue.equals(currentValue)) {
+            put(key, newValue);
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public int size() {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return size() == 0;
+    }
+
+    @Override
+    public boolean containsKey(K key) {
+        return get(key) != null;
+    }
+
+    @Override
+    public boolean containsValue(V value) {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void clear() {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Set<K> keySet() {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Collection<V> values() {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        // TODO
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public V putIfAbsent(K key, V value) {
+        V currentValue = get(key);
+        if (currentValue == null) {
+            put(key, value);
+            return null;
+        }
+        return currentValue;
+    }
+
+    protected List<UpdateOperation<String, byte[]>> prepareDatabaseUpdates() {
+        List<UpdateOperation<K, V>> updates = Lists.newLinkedList();
+        deleteSet.forEach(key -> {
+            Versioned<V> original = readCache.get(key);
+            if (original != null) {
+                updates.add(UpdateOperation.<K, V>newBuilder()
+                        .withTableName(name)
+                        .withType(UpdateOperation.Type.REMOVE_IF_VERSION_MATCH)
+                        .withKey(key)
+                        .withCurrentVersion(original.version())
+                        .build());
+            }
+        });
+        writeCache.forEach((key, value) -> {
+            Versioned<V> original = readCache.get(key);
+            if (original == null) {
+                updates.add(UpdateOperation.<K, V>newBuilder()
+                        .withTableName(name)
+                        .withType(UpdateOperation.Type.PUT_IF_ABSENT)
+                        .withKey(key)
+                        .withValue(value)
+                        .build());
+            } else {
+                updates.add(UpdateOperation.<K, V>newBuilder()
+                        .withTableName(name)
+                        .withType(UpdateOperation.Type.PUT_IF_VERSION_MATCH)
+                        .withKey(key)
+                        .withCurrentVersion(original.version())
+                        .withValue(value)
+                        .build());
+            }
+        });
+        return updates.stream().map(this::toRawUpdateOperation).collect(Collectors.toList());
+    }
+
+    private UpdateOperation<String, byte[]> toRawUpdateOperation(UpdateOperation<K, V> update) {
+
+        UpdateOperation.Builder<String, byte[]> rawUpdate = UpdateOperation.<String, byte[]>newBuilder();
+
+        rawUpdate = rawUpdate.withKey(HexString.toHexString(serializer.encode(update.key())))
+            .withCurrentVersion(update.currentVersion())
+            .withType(update.type());
+
+        rawUpdate = rawUpdate.withTableName(update.tableName());
+
+        if (update.value() != null) {
+            rawUpdate = rawUpdate.withValue(serializer.encode(update.value()));
+        }
+
+        if (update.currentValue() != null) {
+            rawUpdate = rawUpdate.withCurrentValue(serializer.encode(update.currentValue()));
+        }
+
+        return rawUpdate.build();
+    }
+
+    /**
+     * Discards all changes made to this transactional map.
+     */
+    protected void rollback() {
+        readCache.clear();
+        writeCache.clear();
+        deleteSet.clear();
+    }
+}
\ No newline at end of file