diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 475d8d1..9ff9c0f 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -343,7 +343,7 @@ function install_begin_request(&$install_state) {
   drupal_load('module', 'system');
 
   require_once DRUPAL_ROOT . '/core/includes/cache.inc';
-  $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
+  $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\MemoryBackend');
 
   // The install process cannot use the database lock backend since the database
   // is not fully up, so we use a null backend implementation during the
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 56b862f..16974a5 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -140,9 +140,6 @@ function update_prepare_d8_bootstrap() {
   // compatible yet. Use the null backend by default to avoid exceptions.
   $GLOBALS['conf']['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
   drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);
-  // Now remove the cache override.
-  unset($GLOBALS['conf']['cache_classes']['cache']);
-  drupal_static_reset('cache');
 
   // If the site has not updated to Drupal 8 yet, check to make sure that it is
   // running an up-to-date version of Drupal 7 before proceeding. Note this has
@@ -414,6 +411,9 @@ function update_prepare_d8_bootstrap() {
         db_change_field('url_alias', 'language', 'langcode', $langcode_spec, $langcode_indexes);
       }
     }
+  // Now remove the cache override.
+  unset($GLOBALS['conf']['cache_classes']['cache']);
+  drupal_static_reset('cache');
   }
 }
 
diff --git a/core/lib/Drupal/Core/Database/Query/Merge.php b/core/lib/Drupal/Core/Database/Query/Merge.php
index b2db00f..a22fc3c 100644
--- a/core/lib/Drupal/Core/Database/Query/Merge.php
+++ b/core/lib/Drupal/Core/Database/Query/Merge.php
@@ -124,11 +124,15 @@ class Merge extends Query implements ConditionInterface {
   protected $needsUpdate = FALSE;
 
   /**
-   * TRUE when execute() runs for the second time.
+   * TRUE when Merge::execute() runs for the second time.
    *
-   * @var boolean
+   * There could have been a deadlock problem with another transaction. This
+   * flag is used to retry exactly once and if that still fails, assume a
+   * permament failure and abort.
+   *
+   * @var bool
    */
-  protected $retry = FALSE;
+  protected $secondTry = FALSE;
 
   /**
   * Constructs a Merge object.
@@ -423,16 +427,17 @@ public function execute() {
           $insert->useDefaults($this->defaultFields);
         }
         $insert->execute();
-        $this->retry = FALSE;
+        $this->secondTry = FALSE;
         return self::STATUS_INSERT;
       }
       catch (IntegrityConstraintViolationException $e) {
-        // Retry only once.
-        if ($this->retry) {
-          throw $e;
+        // Could be a temporary problem (lock), retry once.
+        if (!$this->secondTry) {
+          $this->secondTry = TRUE;
+          return $this->execute();
         }
-        $this->retry = TRUE;
-        return $this->execute();
+        // In case we already tried a second time, throw the exception.
+        throw $e;
       }
     }
     if ($this->needsUpdate) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php b/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
index 37d893d..cde0aeb 100644
--- a/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/DrupalKernel/DrupalKernelTest.php
@@ -26,11 +26,8 @@ public static function getInfo() {
     );
   }
 
-  /**
-   * Tests DIC compilation.
-   */
-  function testCompileDIC() {
-    $classloader = drupal_classloader();
+  function setUp() {
+    parent::setUp();
     global $conf;
     $conf['php_storage']['service_container']= array(
       'bin' => 'service_container',
@@ -38,7 +35,15 @@ function testCompileDIC() {
       'directory' => DRUPAL_ROOT . '/' . variable_get('file_public_path', conf_path() . '/files') . '/php',
       'secret' => $GLOBALS['drupal_hash_salt'],
     );
-    $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
+    // Use a non-persistent cache to avoid queries to non-existing tables.
+    $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\MemoryBackend');
+  }
+
+  /**
+   * Tests DIC compilation.
+   */
+  function testCompileDIC() {
+    $classloader = drupal_classloader();
     // @todo: write a memory based storage backend for testing.
     $module_enabled = array(
       'system' => 'system',
@@ -61,6 +66,7 @@ function testCompileDIC() {
 
     // Now use the read-only storage implementation, simulating a "production"
     // environment.
+    global $conf;
     $conf['php_storage']['service_container']['class'] = 'Drupal\Component\PhpStorage\FileReadOnlyStorage';
     $kernel = new DrupalKernel('testing', FALSE, $classloader);
     $kernel->updateModules($module_enabled);
@@ -106,6 +112,5 @@ function testCompileDIC() {
     // Check that the location of the new module is registered.
     $modules = $container->getParameter('container.modules');
     $this->assertEqual($modules['bundle_test'], drupal_get_filename('module', 'bundle_test'));
-    unset($conf['cache_classes']);
   }
 }
diff --git a/core/modules/views/lib/Drupal/views/ViewsDataCache.php b/core/modules/views/lib/Drupal/views/ViewsDataCache.php
index b117d52..89c7ff0 100644
--- a/core/modules/views/lib/Drupal/views/ViewsDataCache.php
+++ b/core/modules/views/lib/Drupal/views/ViewsDataCache.php
@@ -215,9 +215,11 @@ public function __destruct() {
           $this->set($cid, $data);
         }
       }
-    } catch (\Exception $e) {
-      // During testing the table is gone before this fires. Nasty.
-      // @todo remove after http://drupal.org/node/512026.
+    }
+    catch (\Exception $e) {
+      // During testing the table is gone before this fires.
+      // @todo Use terminate() instead of __destruct(), see
+      //   http://drupal.org/node/512026.
     }
   }