diff -u b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManager.php b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManager.php
--- b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManager.php
@@ -73,30 +73,26 @@
       // Process entity type definition changes.
       if (!empty($change_list['entity_type']) && $change_list['entity_type'] == static::DEFINITION_UPDATED) {
         $entity_type = $this->entityManager->getDefinition($entity_type_id);
-        // @todo Support non-storage-schema-changing definition updates too:
-        //   https://www.drupal.org/node/2336895.
-        $summary[$entity_type_id][] = $this->t('The %entity_type entity type has definition updates that require schema changes.', array('%entity_type' => $entity_type->getLabel()));
+        $summary[$entity_type_id][] = $this->t('Update the %entity_type entity type.', array('%entity_type' => $entity_type->getLabel()));
       }
 
       // Process field storage definition changes.
       if (!empty($change_list['field_storage_definitions'])) {
         $storage_definitions = $this->entityManager->getFieldStorageDefinitions($entity_type_id);
-        $original_storage_definitions = $this->entityManager->getInstalledFieldStorageDefinitions($entity_type_id);
+        $original_storage_definitions = $this->entityManager->getLastInstalledFieldStorageDefinitions($entity_type_id);
 
         foreach ($change_list['field_storage_definitions'] as $field_name => $change) {
           switch ($change) {
             case static::DEFINITION_CREATED:
-              $summary[$entity_type_id][] = $this->t('The %field_name field has been created.', array('%field_name' => $storage_definitions[$field_name]->getLabel()));
+              $summary[$entity_type_id][] = $this->t('Create the %field_name field.', array('%field_name' => $storage_definitions[$field_name]->getLabel()));
               break;
 
             case static::DEFINITION_UPDATED:
-              // @todo Support non-storage-schema-changing definition updates too:
-              //   https://www.drupal.org/node/2336895.
-              $summary[$entity_type_id][] = $this->t('The %field_name field has storage definition updates that require schema changes.', array('%field_name' => $storage_definitions[$field_name]->getLabel()));
+              $summary[$entity_type_id][] = $this->t('Update the %field_name field.', array('%field_name' => $storage_definitions[$field_name]->getLabel()));
               break;
 
             case static::DEFINITION_DELETED:
-              $summary[$entity_type_id][] = $this->t('The %field_name field has been deleted.', array('%field_name' => $original_storage_definitions[$field_name]->getLabel()));
+              $summary[$entity_type_id][] = $this->t('Delete the %field_name field.', array('%field_name' => $original_storage_definitions[$field_name]->getLabel()));
               break;
           }
         }
@@ -114,14 +110,14 @@
       // Process entity type definition changes.
       if (!empty($change_list['entity_type']) && $change_list['entity_type'] == static::DEFINITION_UPDATED) {
         $entity_type = $this->entityManager->getDefinition($entity_type_id);
-        $original = $this->entityManager->getInstalledDefinition($entity_type_id);
+        $original = $this->entityManager->getLastInstalledDefinition($entity_type_id);
         $this->entityManager->onEntityTypeUpdate($entity_type, $original);
       }
 
       // Process field storage definition changes.
       if (!empty($change_list['field_storage_definitions'])) {
         $storage_definitions = $this->entityManager->getFieldStorageDefinitions($entity_type_id);
-        $original_storage_definitions = $this->entityManager->getInstalledFieldStorageDefinitions($entity_type_id);
+        $original_storage_definitions = $this->entityManager->getLastInstalledFieldStorageDefinitions($entity_type_id);
 
         foreach ($change_list['field_storage_definitions'] as $field_name => $change) {
           switch ($change) {
@@ -160,7 +156,7 @@
     $change_list = array();
 
     foreach ($this->entityManager->getDefinitions() as $entity_type_id => $entity_type) {
-      $original = $this->entityManager->getInstalledDefinition($entity_type_id);
+      $original = $this->entityManager->getLastInstalledDefinition($entity_type_id);
       // @todo Support non-storage-schema-changing definition updates too:
       //   https://www.drupal.org/node/2336895.
       if ($this->requiresEntityStorageSchemaChanges($entity_type, $original)) {
@@ -170,7 +166,7 @@
       if ($entity_type->isFieldable()) {
         $field_changes = array();
         $storage_definitions = $this->entityManager->getFieldStorageDefinitions($entity_type_id);
-        $original_storage_definitions = $this->entityManager->getInstalledFieldStorageDefinitions($entity_type_id);
+        $original_storage_definitions = $this->entityManager->getLastInstalledFieldStorageDefinitions($entity_type_id);
 
         // Detect created field storage definitions.
         foreach (array_diff_key($storage_definitions, $original_storage_definitions) as $field_name => $storage_definition) {
diff -u b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManagerInterface.php b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManagerInterface.php
--- b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManagerInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityDefinitionUpdateManagerInterface.php
@@ -24,9 +24,9 @@
  * invoke those events. This interface is for managing that.
  *
  * @see \Drupal\Core\Entity\EntityManagerInterface::getDefinition()
- * @see \Drupal\Core\Entity\EntityManagerInterface::getInstalledDefinition()
+ * @see \Drupal\Core\Entity\EntityManagerInterface::getLastInstalledDefinition()
  * @see \Drupal\Core\Entity\EntityManagerInterface::getFieldStorageDefinitions()
- * @see \Drupal\Core\Entity\EntityManagerInterface::getInstalledFieldStorageDefinitions()
+ * @see \Drupal\Core\Entity\EntityManagerInterface::getLastInstalledFieldStorageDefinitions()
  * @see \Drupal\Core\Entity\EntityTypeListenerInterface
  * @see \Drupal\Core\Field\FieldStorageDefinitionListenerInterface
  */
diff -u b/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
--- b/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -205,6 +205,7 @@
     $this->clearCachedBundles();
     $this->clearCachedFieldDefinitions();
     $this->classNameEntityTypeMap = array();
+    $this->handlers = array();
   }
 
   /**
@@ -985,9 +986,9 @@
       $storage->onEntityTypeCreate($entity_type);
     }
 
-    $this->setInstalledDefinition($entity_type);
+    $this->setLastInstalledDefinition($entity_type);
     if ($entity_type->isFieldable()) {
-      $this->setInstalledFieldStorageDefinitions($entity_type_id, $this->getFieldStorageDefinitions($entity_type_id));
+      $this->setLastInstalledFieldStorageDefinitions($entity_type_id, $this->getFieldStorageDefinitions($entity_type_id));
     }
   }
 
@@ -1004,7 +1005,7 @@
       $storage->onEntityTypeUpdate($entity_type, $original);
     }
 
-    $this->setInstalledDefinition($entity_type);
+    $this->setLastInstalledDefinition($entity_type);
   }
 
   /**
@@ -1020,7 +1021,7 @@
       $storage->onEntityTypeDelete($entity_type);
     }
 
-    $this->deleteInstalledDefinition($entity_type_id);
+    $this->deleteLastInstalledDefinition($entity_type_id);
   }
 
   /**
@@ -1036,7 +1037,7 @@
       $storage->onFieldStorageDefinitionCreate($storage_definition);
     }
 
-    $this->setInstalledFieldStorageDefinition($storage_definition);
+    $this->setLastInstalledFieldStorageDefinition($storage_definition);
     $this->clearCachedFieldDefinitions();
   }
 
@@ -1053,7 +1054,7 @@
       $storage->onFieldStorageDefinitionUpdate($storage_definition, $original);
     }
 
-    $this->setInstalledFieldStorageDefinition($storage_definition);
+    $this->setLastInstalledFieldStorageDefinition($storage_definition);
     $this->clearCachedFieldDefinitions();
   }
 
@@ -1070,7 +1071,7 @@
       $storage->onFieldStorageDefinitionDelete($storage_definition);
     }
 
-    $this->deleteInstalledFieldStorageDefinition($storage_definition);
+    $this->deleteLastInstalledFieldStorageDefinition($storage_definition);
     $this->clearCachedFieldDefinitions();
   }
 
@@ -1131,7 +1132,7 @@
   /**
    * {@inheritdoc}
    */
-  public function getInstalledDefinition($entity_type_id) {
+  public function getLastInstalledDefinition($entity_type_id) {
     return $this->state->get('entity.manager.' . $entity_type_id . '.entity_type');
   }
 
@@ -1141,7 +1142,7 @@
    * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
    *   The entity type definition.
    */
-  protected function setInstalledDefinition(EntityTypeInterface $entity_type) {
+  protected function setLastInstalledDefinition(EntityTypeInterface $entity_type) {
     $entity_type_id = $entity_type->id();
     $this->state->set('entity.manager.' . $entity_type_id . '.entity_type', $entity_type);
   }
@@ -1152,7 +1153,7 @@
    * @param string $entity_type_id
    *   The entity type definition identifier.
    */
-  protected function deleteInstalledDefinition($entity_type_id) {
+  protected function deleteLastInstalledDefinition($entity_type_id) {
     $this->state->delete('entity.manager.' . $entity_type_id . '.entity_type');
     // Clean up field storage definitions as well. Even if the entity type
     // isn't currently fieldable, there might be legacy definitions or an
@@ -1163,7 +1164,7 @@
   /**
    * {@inheritdoc}
    */
-  public function getInstalledFieldStorageDefinitions($entity_type_id) {
+  public function getLastInstalledFieldStorageDefinitions($entity_type_id) {
     return $this->state->get('entity.manager.' . $entity_type_id . '.field_storage_definitions');
   }
 
@@ -1175,7 +1176,7 @@
    * @param \Drupal\Core\Field\FieldStorageDefinitionInterface[] $storage_definitions
    *   An array of field storage definitions.
    */
-  protected function setInstalledFieldStorageDefinitions($entity_type_id, array $storage_definitions) {
+  protected function setLastInstalledFieldStorageDefinitions($entity_type_id, array $storage_definitions) {
     $this->state->set('entity.manager.' . $entity_type_id . '.field_storage_definitions', $storage_definitions);
   }
 
@@ -1185,11 +1186,11 @@
    * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
    *   The field storage definition.
    */
-  protected function setInstalledFieldStorageDefinition(FieldStorageDefinitionInterface $storage_definition) {
+  protected function setLastInstalledFieldStorageDefinition(FieldStorageDefinitionInterface $storage_definition) {
     $entity_type_id = $storage_definition->getTargetEntityTypeId();
-    $definitions = $this->getInstalledFieldStorageDefinitions($entity_type_id);
+    $definitions = $this->getLastInstalledFieldStorageDefinitions($entity_type_id);
     $definitions[$storage_definition->getName()] = $storage_definition;
-    $this->setInstalledFieldStorageDefinitions($entity_type_id, $definitions);
+    $this->setLastInstalledFieldStorageDefinitions($entity_type_id, $definitions);
   }
 
   /**
@@ -1198,11 +1199,11 @@
    * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
    *   The field storage definition.
    */
-  protected function deleteInstalledFieldStorageDefinition(FieldStorageDefinitionInterface $storage_definition) {
+  protected function deleteLastInstalledFieldStorageDefinition(FieldStorageDefinitionInterface $storage_definition) {
     $entity_type_id = $storage_definition->getTargetEntityTypeId();
-    $definitions = $this->getInstalledFieldStorageDefinitions($entity_type_id);
+    $definitions = $this->getLastInstalledFieldStorageDefinitions($entity_type_id);
     unset($definitions[$storage_definition->getName()]);
-    $this->setInstalledFieldStorageDefinitions($entity_type_id, $definitions);
+    $this->setLastInstalledFieldStorageDefinitions($entity_type_id, $definitions);
   }
 
 }
diff -u b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
--- b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityManagerInterface.php
@@ -96,7 +96,8 @@
    * definitions for which database tables were created.
    *
    * Application management code can check if getFieldStorageDefinitions()
-   * differs from getInstalledFieldStorageDefinitions() and decide whether to:
+   * differs from getLastInstalledFieldStorageDefinitions() and decide whether
+   * to:
    * - Invoke the appropriate
    *   \Drupal\Core\Field\FieldStorageDefinitionListenerInterface
    *   events so that handlers react to the new definitions.
@@ -113,7 +114,7 @@
    *
    * @see \Drupal\Core\Entity\EntityTypeListenerInterface
    */
-  public function getInstalledFieldStorageDefinitions($entity_type_id);
+  public function getLastInstalledFieldStorageDefinitions($entity_type_id);
 
   /**
    * Returns a lightweight map of fields across bundles.
@@ -334,7 +335,7 @@
    * definition for which database tables were created.
    *
    * Application management code can check if getDefinition() differs from
-   * getInstalledDefinition() and decide whether to:
+   * getLastInstalledDefinition() and decide whether to:
    * - Invoke the appropriate \Drupal\Core\Entity\EntityTypeListenerInterface
    *   event so that handlers react to the new definition.
    * - Raise a warning that the application state is incompatible with the
@@ -350,7 +351,7 @@
    *
    * @see \Drupal\Core\Entity\EntityTypeListenerInterface
    */
-  public function getInstalledDefinition($entity_type_id);
+  public function getLastInstalledDefinition($entity_type_id);
 
   /**
    * {@inheritdoc}
diff -u b/core/lib/Drupal/Core/Entity/Schema/EntityStorageSchemaInterface.php b/core/lib/Drupal/Core/Entity/Schema/EntityStorageSchemaInterface.php
--- b/core/lib/Drupal/Core/Entity/Schema/EntityStorageSchemaInterface.php
+++ b/core/lib/Drupal/Core/Entity/Schema/EntityStorageSchemaInterface.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\Core\Entity\Schema;
+
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\EntityTypeListenerInterface;
 
@@ -16,12 +17,9 @@
  * storage backend's schema that the entity type's storage handler needs for
  * storing its entities. For example, if the storage handler is for a SQL
  * backend, then the storage schema handler is responsible for creating the
- * needed tables.
- *
- * During the life of the website, an entity type's definition can change in a
- * way that requires changes to the storage schema, so the handler must react
- * to the various \Drupal\Core\Entity\EntityTypeListenerInterface events
- * accordingly.
+ * needed tables. During the application lifetime, an entity type's definition
+ * can change in a way that requires changes to the storage schema, so this
+ * interface defines methods for that as well.
  *
  * @see \Drupal\Core\Entity\EntityStorageInterface
  */
@@ -43,16 +41,18 @@
   /**
    * Checks if existing data would be lost if the schema changes were applied.
    *
-   * This is only called if requiresEntityStorageSchemaChanges() returns TRUE,
-   * since if there are no schema changes, then no data needs to be migrated,
-   * so this function does not need to recheck whether schema changes are
-   * needed.
+   * If there are no schema changes needed, then no data needs to be migrated,
+   * but it is not the responsibility of this function to recheck what
+   * requiresEntityStorageSchemaChanges() checks. Rather, the meaning of what
+   * this function returns when requiresEntityStorageSchemaChanges() returns
+   * FALSE is undefined. Callers are expected to only call this function when
+   * requiresEntityStorageSchemaChanges() is TRUE.
    *
-   * This function can return TRUE if any of these conditions apply:
+   * This function can return FALSE if any of these conditions apply:
    * - There are no existing entities for the entity type.
    * - There are existing entities, but the schema changes can be applied
-   *   without losing their data (e.g., if the schema change can involve
-   *   altering tables instead of dropping and recreating them).
+   *   without losing their data (e.g., if the schema changes can be performed
+   *   by altering tables rather than dropping and recreating them).
    * - The only entity data that would be lost are ones that are not valid for
    *   the new definition (e.g., if changing an entity type from revisionable
    *   to non-revisionable, then it's okay to drop data for the non-default
diff -u b/core/lib/Drupal/Core/Entity/Schema/FieldableEntityStorageSchemaInterface.php b/core/lib/Drupal/Core/Entity/Schema/FieldableEntityStorageSchemaInterface.php
--- b/core/lib/Drupal/Core/Entity/Schema/FieldableEntityStorageSchemaInterface.php
+++ b/core/lib/Drupal/Core/Entity/Schema/FieldableEntityStorageSchemaInterface.php
@@ -31,19 +31,21 @@
   /**
    * Checks if existing data would be lost if the schema changes were applied.
    *
-   * This is only called if requiresFieldStorageSchemaChanges() returns TRUE,
-   * since if there are no schema changes, then no data needs to be migrated,
-   * so this function does not need to recheck whether schema changes are
-   * needed.
+   * If there are no schema changes needed, then no data needs to be migrated,
+   * but it is not the responsibility of this function to recheck what
+   * requiresFieldStorageSchemaChanges() checks. Rather, the meaning of what
+   * this function returns when requiresFieldStorageSchemaChanges() returns
+   * FALSE is undefined. Callers are expected to only call this function when
+   * requiresFieldStorageSchemaChanges() is TRUE.
    *
-   * This function can return TRUE if any of these conditions apply:
+   * This function can return FALSE if any of these conditions apply:
    * - There are no existing entities for the entity type to which this field
    *   is attached.
    * - There are existing entities, but none with existing values for this
    *   field.
    * - There are existing field values, but the schema changes can be applied
-   *   without losing them (e.g., if the schema change can involve altering
-   *   tables instead of dropping and recreating them).
+   *   without losing them (e.g., if the schema changes can be performed by
+   *   altering tables rather than dropping and recreating them).
    * - The only field values that would be lost are ones that are not valid for
    *   the new definition (e.g., if changing a field from revisionable to
    *   non-revisionable, then it's okay to drop data for the non-default
diff -u b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
--- b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php
@@ -299,11 +299,7 @@
       ), $all_fields);
 
       $revisionable = $this->entityType->isRevisionable();
-      // @todo Remove the data table check once all entity types are using
-      // entity query and we have a views data handler. See:
-      // - https://drupal.org/node/2068325
-      // - https://drupal.org/node/1740492
-      $translatable = $this->entityType->getDataTable() && $this->entityType->isTranslatable();
+      $translatable = $this->entityType->isTranslatable();
       if (!$revisionable && !$translatable) {
         // The base layout stores all the base field values in the base table.
         $table_mapping->setFieldNames($this->baseTable, $all_fields);
diff -u b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageTest.php b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageTest.php
--- b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageTest.php
@@ -598,10 +598,10 @@
     // This allows to re-use the data provider.
     $entity_keys['langcode'] = 'langcode';
 
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('isTranslatable')
       ->will($this->returnValue(TRUE));
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('getDataTable')
       ->will($this->returnValue('entity_test_field_data'));
     $this->entityType->expects($this->any())
@@ -658,10 +658,10 @@
     $field_names = array_merge(array_values(array_filter($entity_keys)), $base_field_names);
     $this->fieldDefinitions = $this->mockFieldDefinitions($field_names);
 
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('isTranslatable')
       ->will($this->returnValue(TRUE));
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('getDataTable')
       ->will($this->returnValue('entity_test_field_data'));
     $this->entityType->expects($this->any())
@@ -720,13 +720,13 @@
       'langcode' => 'langcode',
     );
 
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('isRevisionable')
       ->will($this->returnValue(TRUE));
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('isTranslatable')
       ->will($this->returnValue(TRUE));
-    $this->entityType->expects($this->exactly(2))
+    $this->entityType->expects($this->atLeastOnce())
       ->method('getDataTable')
       ->will($this->returnValue('entity_test_field_data'));
     $this->entityType->expects($this->any())
@@ -841,13 +841,13 @@
       $revisionable_field_names = array('description', 'owner');
       $this->fieldDefinitions += $this->mockFieldDefinitions(array_merge($revisionable_field_names, $revision_metadata_field_names), array('isRevisionable' => TRUE));
 
-      $this->entityType->expects($this->exactly(2))
+      $this->entityType->expects($this->atLeastOnce())
         ->method('isRevisionable')
         ->will($this->returnValue(TRUE));
-      $this->entityType->expects($this->exactly(2))
+      $this->entityType->expects($this->atLeastOnce())
         ->method('isTranslatable')
         ->will($this->returnValue(TRUE));
-      $this->entityType->expects($this->exactly(2))
+      $this->entityType->expects($this->atLeastOnce())
         ->method('getDataTable')
         ->will($this->returnValue('entity_test_field_data'));
       $this->entityType->expects($this->any())
only in patch2:
unchanged:
--- a/core/modules/field/tests/modules/field_test/field_test.entity.inc
+++ b/core/modules/field/tests/modules/field_test/field_test.entity.inc
@@ -18,11 +18,17 @@ function field_test_entity_type_alter(array &$entity_types) {
 /**
  * Helper function to enable entity translations.
  */
-function field_test_entity_info_translatable($entity_type = NULL, $translatable = NULL) {
+function field_test_entity_info_translatable($entity_type_id = NULL, $translatable = NULL) {
   $stored_value = &drupal_static(__FUNCTION__, array());
-  if (isset($entity_type)) {
-    $stored_value[$entity_type] = $translatable;
-    \Drupal::entityManager()->clearCachedDefinitions();
+  if (isset($entity_type_id)) {
+    $entity_manager = \Drupal::entityManager();
+    $original = $entity_manager->getDefinition($entity_type_id);
+    $stored_value[$entity_type_id] = $translatable;
+    if ($translatable != $original->isTranslatable()) {
+      $entity_manager->clearCachedDefinitions();
+      $entity_type = $entity_manager->getDefinition($entity_type_id);
+      $entity_manager->onEntityTypeUpdate($entity_type, $original);
+    }
   }
   return $stored_value;
 }
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/src/Tests/Entity/EntityDefinitionUpdateTest.php
@@ -0,0 +1,116 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\system\Tests\Entity\EntityDefinitionUpdateTest.
+ */
+
+namespace Drupal\system\Tests\Entity;
+
+use Drupal\Core\Entity\EntityStorageException;
+
+/**
+ * Tests EntityDefinitionUpdateManager functionality.
+ *
+ * @group Entity
+ */
+class EntityDefinitionUpdateTest extends EntityUnitTestBase {
+
+  /**
+   * The entity definition update manager.
+   *
+   * @var \Drupal\Core\Entity\EntityDefinitionUpdateManagerInterface
+   */
+  protected $entityDefinitionUpdateManager;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection
+   */
+  protected $database;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->entityDefinitionUpdateManager = $this->container->get('entity.definition_update_manager');
+    $this->database = $this->container->get('database');
+  }
+
+  /**
+   * Tests when no definition update is needed.
+   */
+  public function testNoUpdates() {
+    // Install every entity type's schema.
+    foreach ($this->entityManager->getDefinitions() as $entity_type_id => $entity_type) {
+      $this->installEntitySchema($entity_type_id);
+    }
+
+    // Ensure that the definition update manager reports no updates.
+    $this->assertFalse($this->entityDefinitionUpdateManager->needsUpdates(), 'EntityDefinitionUpdateManager reports that no updates are needed.');
+    $this->assertIdentical($this->entityDefinitionUpdateManager->getChangeSummary(), array(), 'EntityDefinitionUpdateManager reports an empty change summary.');
+
+    // Ensure that applyUpdates() runs without error (it's not expected to do
+    // anything when there aren't updates).
+    $this->entityDefinitionUpdateManager->applyUpdates();
+  }
+
+  /**
+   * Tests updating entity schema when there are no existing entities.
+   */
+  public function testUpdateWithoutData() {
+    // Install every entity type's schema. Start with entity_test_rev not
+    // supporting revisions, and ensure its revision table isn't created.
+    $this->state->set('entity_test.entity_test_rev.disable_revisable', TRUE);
+    $this->entityManager->clearCachedDefinitions();
+    foreach ($this->entityManager->getDefinitions() as $entity_type_id => $entity_type) {
+      $this->installEntitySchema($entity_type_id);
+    }
+    $this->assertFalse($this->database->schema()->tableExists('entity_test_rev_revision'), 'Revision table not created for entity_test_rev.');
+
+    // Restore entity_test_rev back to supporting revisions and ensure the
+    // definition update manager reports that an update is needed.
+    $this->state->delete('entity_test.entity_test_rev.disable_revisable');
+    $this->assertTrue($this->entityDefinitionUpdateManager->needsUpdates(), 'EntityDefinitionUpdateManager reports that updates are needed.');
+    $expected = array(
+      'entity_test_rev' => array(
+        t('Update the %entity_type entity type.', array('%entity_type' => $this->entityManager->getDefinition('entity_test_rev')->getLabel())),
+      ),
+    );
+    $this->assertIdentical($this->entityDefinitionUpdateManager->getChangeSummary(), $expected, 'EntityDefinitionUpdateManager reports the expected change summary.');
+
+    // Run the update and ensure the revision table is created.
+    $this->entityDefinitionUpdateManager->applyUpdates();
+    $this->assertTrue($this->database->schema()->tableExists('entity_test_rev_revision'), 'Revision table created for entity_test_rev.');
+  }
+
+  /**
+   * Tests updating entity schema when there are existing entities.
+   */
+  public function testUpdateWithData() {
+    // Install every entity type's schema. Start with entity_test_rev not
+    // supporting revisions.
+    $this->state->set('entity_test.entity_test_rev.disable_revisable', TRUE);
+    $this->entityManager->clearCachedDefinitions();
+    foreach ($this->entityManager->getDefinitions() as $entity_type_id => $entity_type) {
+      $this->installEntitySchema($entity_type_id);
+    }
+
+    // Save an entity.
+    $this->entityManager->getStorage('entity_test_rev')->create()->save();
+
+    // Restore entity_test_rev back to supporting revisions and try to apply
+    // the update. It's expected to throw an exception.
+    $this->state->delete('entity_test.entity_test_rev.disable_revisable');
+    try {
+      $this->entityDefinitionUpdateManager->applyUpdates();
+      $this->fail('EntityStorageException thrown when trying to apply an update that requires data migration.');
+    }
+    catch (EntityStorageException $e) {
+      $this->pass('EntityStorageException thrown when trying to apply an update that requires data migration.');
+    }
+  }
+
+}
only in patch2:
unchanged:
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -5,20 +5,21 @@
  * Configuration system that lets administrators modify the workings of the site.
  */
 
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\Core\Block\BlockPluginInterface;
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\ContentEntityTypeInterface;
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ExtensionDiscovery;
-use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Routing\RouteMatchInterface;
-use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Menu\MenuTreeParameters;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Core\Url;
-use Drupal\Core\Block\BlockPluginInterface;
 use Drupal\user\UserInterface;
-use Symfony\Component\HttpFoundation\RedirectResponse;
 use GuzzleHttp\Exception\RequestException;
+use Symfony\Component\HttpFoundation\RedirectResponse;
 
 /**
  * New users will be set to the default time zone at registration.
@@ -1032,11 +1033,48 @@ function system_sort_themes($a, $b) {
  * Implements hook_system_info_alter().
  */
 function system_system_info_alter(&$info, Extension $file, $type) {
-  // Remove page-top and page-bottom from the blocks UI since they are reserved for
-  // modules to populate from outside the blocks system.
-  if ($type == 'theme') {
-    $info['regions_hidden'][] = 'page_top';
-    $info['regions_hidden'][] = 'page_bottom';
+  switch ($type) {
+    case 'theme':
+      // Remove page-top and page-bottom from the blocks UI since they are
+      // reserved for modules to populate from outside the blocks system.
+      $info['regions_hidden'][] = 'page_top';
+      $info['regions_hidden'][] = 'page_bottom';
+      break;
+
+    case 'module':
+      // @todo Unify this with field_system_info_alter() once purging is
+      //   supported for any field. See https://www.drupal.org/node/2282119.
+      $module_name = $file->getName();
+      if ($module_name != 'field') {
+        $entity_manager = \Drupal::entityManager();
+        foreach ($entity_manager->getDefinitions() as $entity_type_id => $entity_type) {
+          try {
+            // We skip entity-defining modules, otherwise deleting all entities
+            // would be required before being able to uninstall them.
+            if ($entity_type instanceof ContentEntityTypeInterface && $entity_type->getProvider() != $module_name) {
+              $storage_definitions = $entity_manager->getFieldStorageDefinitions($entity_type_id);
+              // @todo Make it easier to query if there are entities:
+              //   https://www.drupal.org/node/2337753.
+              $has_data = $entity_manager->getStorage($entity_type_id)->countFieldData($storage_definitions[$entity_type->getKey('id')], TRUE);
+              if ($has_data) {
+                foreach ($storage_definitions as $storage_definition) {
+                  if ($storage_definition->getProvider() == $module_name) {
+                    $info['required'] = TRUE;
+                    $info['explanation'] = t('Fields type(s) in use');
+                    break;
+                  }
+                }
+              }
+            }
+          }
+          catch (PluginNotFoundException $e) {
+            // This may happen if the current module is being installed. In this
+            // case we can safely ignore it, as we are interested in blocking
+            // module uninstallation.
+          }
+        }
+      }
+      break;
   }
 }
 
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/entity_test/entity_test.module
+++ b/core/modules/system/tests/modules/entity_test/entity_test.module
@@ -71,6 +71,14 @@ function entity_test_entity_type_alter(array &$entity_types) {
       $entity_types[$entity_type]->set('translation', $translation);
     }
   }
+
+  // Optionally allow testing an entity type definition being updated from
+  // revisable to not or vice versa.
+  if (\Drupal::state()->get('entity_test.entity_test_rev.disable_revisable')) {
+    $keys = $entity_types['entity_test_rev']->getKeys();
+    unset($keys['revision']);
+    $entity_types['entity_test_rev']->set('entity_keys', $keys);
+  }
 }
 
 /**