diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseEntryExpirationTracker.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseEntryExpirationTracker.java
new file mode 100644
index 0000000..c9775ca
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseEntryExpirationTracker.java
@@ -0,0 +1,191 @@
+/*
+ * Copyright 2014 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.onlab.onos.store.service.impl;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import net.jodah.expiringmap.ExpiringMap;
+import net.jodah.expiringmap.ExpiringMap.ExpirationListener;
+import net.jodah.expiringmap.ExpiringMap.ExpirationPolicy;
+import net.kuujo.copycat.cluster.Member;
+import net.kuujo.copycat.event.EventHandler;
+import net.kuujo.copycat.event.LeaderElectEvent;
+
+import org.onlab.onos.cluster.ClusterService;
+import org.onlab.onos.store.cluster.messaging.ClusterCommunicationService;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.MessageSubject;
+import org.onlab.onos.store.service.DatabaseService;
+import org.onlab.onos.store.service.VersionedValue;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Plugs into the database update stream and track the TTL of entries added to
+ * the database. For tables with pre-configured finite TTL, this class has
+ * mechanisms for expiring (deleting) old, expired entries from the database.
+ */
+public class DatabaseEntryExpirationTracker implements
+        DatabaseUpdateEventListener, EventHandler<LeaderElectEvent> {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    public static final MessageSubject DATABASE_UPDATES = new MessageSubject(
+            "database-update-event");
+
+    private DatabaseService databaseService;
+    private ClusterService cluster;
+    private ClusterCommunicationService clusterCommunicator;
+
+    private final Member localMember;
+    private final AtomicBoolean isLocalMemberLeader = new AtomicBoolean(false);
+
+    private final Map<String, Map<DatabaseRow, VersionedValue>> tableEntryExpirationMap = new HashMap<>();
+
+    private final ExpirationListener<DatabaseRow, VersionedValue> expirationObserver = new ExpirationObserver();
+
+    DatabaseEntryExpirationTracker(Member localMember) {
+        this.localMember = localMember;
+    }
+
+    @Override
+    public void tableModified(TableModificationEvent event) {
+        DatabaseRow row = new DatabaseRow(event.tableName(), event.key());
+        Map<DatabaseRow, VersionedValue> map = tableEntryExpirationMap
+                .get(event.tableName());
+
+        switch (event.type()) {
+        case ROW_DELETED:
+            if (isLocalMemberLeader.get()) {
+                try {
+                    clusterCommunicator.broadcast(new ClusterMessage(cluster
+                            .getLocalNode().id(), DATABASE_UPDATES,
+                            DatabaseStateMachine.SERIALIZER.encode(event)));
+                } catch (IOException e) {
+                    log.error(
+                            "Failed to broadcast a database table modification event.",
+                            e);
+                }
+            }
+            break;
+        case ROW_ADDED:
+        case ROW_UPDATED:
+            map.put(row, null);
+            break;
+        default:
+            break;
+        }
+    }
+
+    @Override
+    public void tableCreated(String tableName, int expirationTimeMillis) {
+        // make this explicit instead of relying on a negative value
+        // to indicate no expiration.
+        if (expirationTimeMillis > 0) {
+            tableEntryExpirationMap.put(tableName, ExpiringMap.builder()
+                    .expiration(expirationTimeMillis, TimeUnit.SECONDS)
+                    .expirationListener(expirationObserver)
+                    // FIXME: make the expiration policy configurable.
+                    .expirationPolicy(ExpirationPolicy.CREATED).build());
+        }
+    }
+
+    @Override
+    public void tableDeleted(String tableName) {
+        tableEntryExpirationMap.remove(tableName);
+    }
+
+    private class ExpirationObserver implements
+            ExpirationListener<DatabaseRow, VersionedValue> {
+        @Override
+        public void expired(DatabaseRow key, VersionedValue value) {
+            try {
+                if (isLocalMemberLeader.get()) {
+                    if (!databaseService.removeIfVersionMatches(key.tableName,
+                            key.key, value.version())) {
+                        log.info("Entry in the database changed before right its TTL expiration.");
+                    }
+                } else {
+                    // If this node is not the current leader, we should never
+                    // let the expiring entries drop off
+                    // Under stable conditions (i.e no leadership switch) the
+                    // current leader will initiate
+                    // a database remove and this instance will get notified
+                    // of a tableModification event causing it to remove from
+                    // the map.
+                    Map<DatabaseRow, VersionedValue> map = tableEntryExpirationMap
+                            .get(key.tableName);
+                    if (map != null) {
+                        map.put(key, value);
+                    }
+                }
+
+            } catch (Exception e) {
+                log.warn(
+                        "Failed to delete entry from the database after ttl expiration. Will retry eviction",
+                        e);
+                tableEntryExpirationMap.get(key.tableName).put(
+                        new DatabaseRow(key.tableName, key.key), value);
+            }
+        }
+    }
+
+    @Override
+    public void handle(LeaderElectEvent event) {
+        if (localMember.equals(event.leader())) {
+            isLocalMemberLeader.set(true);
+        }
+    }
+
+    /**
+     * Wrapper class for a database row identifier.
+     */
+    private class DatabaseRow {
+
+        String tableName;
+        String key;
+
+        public DatabaseRow(String tableName, String key) {
+            this.tableName = tableName;
+            this.key = key;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (this == obj) {
+                return true;
+            }
+            if (!(obj instanceof DatabaseRow)) {
+                return false;
+            }
+            DatabaseRow that = (DatabaseRow) obj;
+
+            return Objects.equals(this.tableName, that.tableName)
+                    && Objects.equals(this.key, that.key);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(tableName, key);
+        }
+    }
+}
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
index 9ca69ee..62a06b4 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseStateMachine.java
@@ -237,8 +237,8 @@
                     WriteResult putResult = new WriteResult(WriteStatus.OK, previousValue);
                     results.add(putResult);
                     tableModificationEvent = (previousValue == null) ?
-                            TableModificationEvent.rowAdded(request.tableName(), request.key()) :
-                            TableModificationEvent.rowUpdated(request.tableName(), request.key());
+                            TableModificationEvent.rowAdded(request.tableName(), request.key(), newValue) :
+                            TableModificationEvent.rowUpdated(request.tableName(), request.key(), newValue);
                     break;
 
                 case REMOVE:
@@ -249,7 +249,7 @@
                     results.add(removeResult);
                     if (removedValue != null) {
                         tableModificationEvent =
-                                TableModificationEvent.rowDeleted(request.tableName(), request.key());
+                                TableModificationEvent.rowDeleted(request.tableName(), request.key(), removedValue);
                     }
                     break;
 
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventHandler.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventHandler.java
deleted file mode 100644
index 21028e4..0000000
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventHandler.java
+++ /dev/null
@@ -1,172 +0,0 @@
-/*
- * Copyright 2014 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.onlab.onos.store.service.impl;
-
-import java.io.IOException;
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Objects;
-import java.util.concurrent.atomic.AtomicBoolean;
-
-//import net.jodah.expiringmap.ExpiringMap;
-//import net.jodah.expiringmap.ExpiringMap.ExpirationListener;
-//import net.jodah.expiringmap.ExpiringMap.ExpirationPolicy;
-import net.kuujo.copycat.cluster.Member;
-import net.kuujo.copycat.event.EventHandler;
-import net.kuujo.copycat.event.LeaderElectEvent;
-
-import org.onlab.onos.cluster.ClusterService;
-import org.onlab.onos.store.cluster.messaging.ClusterCommunicationService;
-import org.onlab.onos.store.cluster.messaging.ClusterMessage;
-import org.onlab.onos.store.cluster.messaging.MessageSubject;
-import org.onlab.onos.store.service.DatabaseService;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * Database update event handler.
- */
-public class DatabaseUpdateEventHandler implements
-    DatabaseUpdateEventListener, EventHandler<LeaderElectEvent> {
-
-    private final Logger log = LoggerFactory.getLogger(getClass());
-
-    public static final MessageSubject DATABASE_UPDATES =
-            new MessageSubject("database-update-event");
-
-    private DatabaseService databaseService;
-    private ClusterService cluster;
-    private ClusterCommunicationService clusterCommunicator;
-
-    private final Member localMember;
-    private final AtomicBoolean isLocalMemberLeader = new AtomicBoolean(false);
-    private final Map<String, Map<DatabaseRow, Void>> tableEntryExpirationMap = new HashMap<>();
-    //private final ExpirationListener<DatabaseRow, Void> expirationObserver = new ExpirationObserver();
-
-    DatabaseUpdateEventHandler(Member localMember) {
-        this.localMember = localMember;
-    }
-
-    @Override
-    public void tableModified(TableModificationEvent event) {
-        DatabaseRow row = new DatabaseRow(event.tableName(), event.key());
-        Map<DatabaseRow, Void> map = tableEntryExpirationMap.get(event.tableName());
-
-        switch (event.type()) {
-        case ROW_DELETED:
-            if (isLocalMemberLeader.get()) {
-                try {
-                    clusterCommunicator.broadcast(
-                            new ClusterMessage(
-                                    cluster.getLocalNode().id(),
-                                    DATABASE_UPDATES,
-                                    DatabaseStateMachine.SERIALIZER.encode(event)));
-                } catch (IOException e) {
-                    log.error("Failed to broadcast a database table modification event.", e);
-                }
-            }
-            break;
-        case ROW_ADDED:
-        case ROW_UPDATED:
-            map.put(row, null);
-            break;
-        default:
-            break;
-        }
-    }
-
-    @Override
-    public void tableCreated(String tableName, int expirationTimeMillis) {
-        // make this explicit instead of relying on a negative value
-        // to indicate no expiration.
-        if (expirationTimeMillis > 0) {
-            tableEntryExpirationMap.put(tableName, null);
-            /*
-            ExpiringMap.builder()
-                    .expiration(expirationTimeMillis, TimeUnit.SECONDS)
-                    .expirationListener(expirationObserver)
-                    // FIXME: make the expiration policy configurable.
-                    .expirationPolicy(ExpirationPolicy.CREATED)
-                    .build());
-                    */
-        }
-    }
-
-    @Override
-    public void tableDeleted(String tableName) {
-        tableEntryExpirationMap.remove(tableName);
-    }
-
-    /*
-    private class ExpirationObserver implements ExpirationListener<DatabaseRow, Void> {
-        @Override
-        public void expired(DatabaseRow key, Void value) {
-            try {
-                // TODO: The safety of this check needs to be verified.
-                // Couple of issues:
-                // 1. It is very likely that only one member should attempt deletion of the entry from database.
-                // 2. A potential race condition exists where the entry expires, but before its can be deleted
-                // from the database, a new entry is added or existing entry is updated.
-                // That means ttl and expiration should be for a given version.
-                if (isLocalMemberLeader.get()) {
-                    databaseService.remove(key.tableName, key.key);
-                }
-            } catch (Exception e) {
-                log.warn("Failed to delete entry from the database after ttl expiration. Will retry eviction", e);
-                tableEntryExpirationMap.get(key.tableName).put(new DatabaseRow(key.tableName, key.key), null);
-            }
-        }
-    }
-    */
-
-    @Override
-    public void handle(LeaderElectEvent event) {
-        if (localMember.equals(event.leader())) {
-            isLocalMemberLeader.set(true);
-        }
-    }
-
-    private class DatabaseRow {
-
-        String tableName;
-        String key;
-
-        public DatabaseRow(String tableName, String key) {
-            this.tableName = tableName;
-            this.key = key;
-        }
-
-        @Override
-        public boolean equals(Object obj) {
-            if (this == obj) {
-                return true;
-            }
-            if (!(obj instanceof DatabaseRow)) {
-                return false;
-            }
-            DatabaseRow that = (DatabaseRow) obj;
-
-            return Objects.equals(this.tableName, that.tableName) &&
-                   Objects.equals(this.key, that.key);
-        }
-
-        @Override
-        public int hashCode() {
-            return Objects.hash(tableName, key);
-        }
-    }
-}
\ No newline at end of file
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventListener.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventListener.java
index d97191c..1dc0e9d 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventListener.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DatabaseUpdateEventListener.java
@@ -29,15 +29,14 @@
 
     /**
      * Notifies listeners of a table created event.
-     * @param tableName
-     * @param expirationTimeMillis
+     * @param tableName name of the table created
+     * @param expirationTimeMillis TTL for entries added to the table (measured since last update time)
      */
     public void tableCreated(String tableName, int expirationTimeMillis);
 
     /**
      * Notifies listeners of a table deleted event.
-     * @param tableName
+     * @param tableName name of the table deleted
      */
     public void tableDeleted(String tableName);
-
 }
\ No newline at end of file
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
index f83b042..6d99ba7 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
@@ -33,7 +33,8 @@
 
     public static final String ONOS_LOCK_TABLE_NAME = "onos-locks";
 
-    private final ArrayListMultimap<String, LockRequest> locksToAcquire = ArrayListMultimap.create();
+    private final ArrayListMultimap<String, LockRequest> locksToAcquire = ArrayListMultimap
+            .create();
 
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     private ClusterCommunicationService clusterCommunicator;
@@ -61,11 +62,7 @@
 
     @Override
     public Lock create(String path) {
-        return new DistributedLock(
-                path,
-                databaseService,
-                clusterService,
-                this);
+        return new DistributedLock(path, databaseService, clusterService, this);
     }
 
     @Override
@@ -80,21 +77,19 @@
         throw new UnsupportedOperationException();
     }
 
-    protected CompletableFuture<Void> lockIfAvailable(
-            Lock lock,
-            long waitTimeMillis,
-            int leaseDurationMillis) {
+    protected CompletableFuture<Void> lockIfAvailable(Lock lock,
+            long waitTimeMillis, int leaseDurationMillis) {
         CompletableFuture<Void> future = new CompletableFuture<>();
-        locksToAcquire.put(
-                lock.path(),
-                new LockRequest(lock, waitTimeMillis, leaseDurationMillis, future));
+        locksToAcquire.put(lock.path(), new LockRequest(lock, waitTimeMillis,
+                leaseDurationMillis, future));
         return future;
     }
 
     private class LockEventMessageListener implements ClusterMessageHandler {
         @Override
         public void handle(ClusterMessage message) {
-            TableModificationEvent event = DatabaseStateMachine.SERIALIZER.decode(message.payload());
+            TableModificationEvent event = DatabaseStateMachine.SERIALIZER
+                    .decode(message.payload());
             if (!event.tableName().equals(ONOS_LOCK_TABLE_NAME)) {
                 return;
             }
@@ -110,15 +105,20 @@
                     return;
                 }
 
-                Iterator<LockRequest> existingRequestIterator = existingRequests.iterator();
-                while (existingRequestIterator.hasNext()) {
-                    LockRequest request = existingRequestIterator.next();
-                    if (request.expirationTime().isAfter(DateTime.now())) {
-                        existingRequestIterator.remove();
-                    } else {
-                        if (request.lock().tryLock(request.leaseDurationMillis())) {
-                            request.future().complete(null);
-                            existingRequests.remove(0);
+                synchronized (existingRequests) {
+
+                    Iterator<LockRequest> existingRequestIterator = existingRequests
+                            .iterator();
+                    while (existingRequestIterator.hasNext()) {
+                        LockRequest request = existingRequestIterator.next();
+                        if (request.expirationTime().isAfter(DateTime.now())) {
+                            existingRequestIterator.remove();
+                        } else {
+                            if (request.lock().tryLock(
+                                    request.leaseDurationMillis())) {
+                                request.future().complete(null);
+                                existingRequestIterator.remove();
+                            }
                         }
                     }
                 }
@@ -133,14 +133,12 @@
         private final int leaseDurationMillis;
         private final CompletableFuture<Void> future;
 
-        public LockRequest(
-            Lock lock,
-            long waitTimeMillis,
-            int leaseDurationMillis,
-            CompletableFuture<Void> future) {
+        public LockRequest(Lock lock, long waitTimeMillis,
+                int leaseDurationMillis, CompletableFuture<Void> future) {
 
             this.lock = lock;
-            this.expirationTime = DateTime.now().plusMillis((int) waitTimeMillis);
+            this.expirationTime = DateTime.now().plusMillis(
+                    (int) waitTimeMillis);
             this.leaseDurationMillis = leaseDurationMillis;
             this.future = future;
         }
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/TableModificationEvent.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/TableModificationEvent.java
index 885c9fa..b0962dc 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/TableModificationEvent.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/TableModificationEvent.java
@@ -1,5 +1,7 @@
 package org.onlab.onos.store.service.impl;
 
+import org.onlab.onos.store.service.VersionedValue;
+
 /**
  * A table modification event.
  */
@@ -17,41 +19,46 @@
 
     private final String tableName;
     private final String key;
+    private final VersionedValue value;
     private final Type type;
 
     /**
      * Creates a new row deleted table modification event.
      * @param tableName table name.
      * @param key row key
+     * @param value value associated with the key when it was deleted.
      * @return table modification event.
      */
-    public static TableModificationEvent rowDeleted(String tableName, String key) {
-        return new TableModificationEvent(tableName, key, Type.ROW_DELETED);
+    public static TableModificationEvent rowDeleted(String tableName, String key, VersionedValue value) {
+        return new TableModificationEvent(tableName, key, value, Type.ROW_DELETED);
     }
 
     /**
      * Creates a new row added table modification event.
      * @param tableName table name.
      * @param key row key
+     * @param value value associated with the key
      * @return table modification event.
      */
-    public static TableModificationEvent rowAdded(String tableName, String key) {
-        return new TableModificationEvent(tableName, key, Type.ROW_ADDED);
+    public static TableModificationEvent rowAdded(String tableName, String key, VersionedValue value) {
+        return new TableModificationEvent(tableName, key, value, Type.ROW_ADDED);
     }
 
     /**
      * Creates a new row updated table modification event.
      * @param tableName table name.
      * @param key row key
+     * @param newValue value
      * @return table modification event.
      */
-    public static TableModificationEvent rowUpdated(String tableName, String key) {
-        return new TableModificationEvent(tableName, key, Type.ROW_UPDATED);
+    public static TableModificationEvent rowUpdated(String tableName, String key, VersionedValue newValue) {
+        return new TableModificationEvent(tableName, key, newValue, Type.ROW_UPDATED);
     }
 
-    private TableModificationEvent(String tableName, String key, Type type) {
+    private TableModificationEvent(String tableName, String key, VersionedValue value, Type type) {
         this.tableName = tableName;
         this.key = key;
+        this.value = value;
         this.type = type;
     }
 
@@ -72,6 +79,15 @@
     }
 
     /**
+     * Returns the value associated with the key. If the event for a deletion, this
+     * method returns value that was deleted.
+     * @return row value
+     */
+    public VersionedValue value() {
+        return value;
+    }
+
+    /**
      * Returns the type of table modification event.
      * @return event type.
      */