diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index ef50d04..658099e 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -342,17 +342,8 @@ function install_begin_request(&$install_state) {
   module_list(NULL, $module_list);
   drupal_load('module', 'system');
 
-  // Load the cache infrastructure using a "fake" cache implementation that
-  // does not attempt to write to the database. We need this during the initial
-  // part of the installer because the database is not available yet. We
-  // continue to use it even when the database does become available, in order
-  // to preserve consistency between interactive and command-line installations
-  // (the latter complete in one page request and therefore are forced to
-  // continue using the cache implementation they started with) and also
-  // because any data put in the cache during the installer is inherently
-  // suspect, due to the fact that Drupal is not fully set up yet.
   require_once DRUPAL_ROOT . '/core/includes/cache.inc';
-  $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\InstallBackend');
+  $conf['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
 
   // 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/install.inc b/core/includes/install.inc
index 99cfcf6..a3045bf 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -422,6 +422,8 @@ function drupal_verify_profile($install_state) {
 function drupal_install_system() {
   // Create tables.
   drupal_install_schema('system');
+  unset($GLOBALS['conf']['cache_classes']['cache']);
+  drupal_static_reset('cache');
   // Immediately boot a kernel to have real services ready.
   $kernel = new DrupalKernel('install', FALSE, drupal_classloader(), FALSE);
   $kernel->boot();
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 299a81c..6102672 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -136,7 +136,10 @@ function update_prepare_d8_bootstrap() {
   }
 
   // Bootstrap the database.
+  $GLOBALS['conf']['cache_classes'] = array('cache' => 'Drupal\Core\Cache\NullBackend');
   drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);
+  unset($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
@@ -195,6 +198,116 @@ function update_prepare_d8_bootstrap() {
         );
         db_create_table('key_value', $specs);
       }
+      if (!db_table_exists('cache_tags')) {
+        $table = array(
+          'description' => 'Cache table for tracking cache tags related to the cache bin.',
+          'fields' => array(
+            'tag' => array(
+              'description' => 'Namespace-prefixed tag string.',
+              'type' => 'varchar',
+              'length' => 255,
+              'not null' => TRUE,
+              'default' => '',
+            ),
+            'invalidations' => array(
+              'description' => 'Number incremented when the tag is invalidated.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+            'deletions' => array(
+              'description' => 'Number incremented when the tag is deleted.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+          ),
+          'primary key' => array('tag'),
+        );
+        db_create_table('cache_tags', $table);
+      }
+      if (!db_table_exists('cache_config')) {
+        $spec = array(
+          'description' =>  'Cache table for configuration data.',
+          'fields' => array(
+            'cid' => array(
+              'description' => 'Primary Key: Unique cache ID.',
+              'type' => 'varchar',
+              'length' => 255,
+              'not null' => TRUE,
+              'default' => '',
+            ),
+            'data' => array(
+              'description' => 'A collection of data to cache.',
+              'type' => 'blob',
+              'not null' => FALSE,
+              'size' => 'big',
+            ),
+            'expire' => array(
+              'description' => 'A Unix timestamp indicating when the cache entry should expire, or 0 for never.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+            'created' => array(
+              'description' => 'A Unix timestamp indicating when the cache entry was created.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+            'serialized' => array(
+              'description' => 'A flag to indicate whether content is serialized (1) or not (0).',
+              'type' => 'int',
+              'size' => 'small',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+            'tags' => array(
+              'description' => 'Space-separated list of cache tags for this entry.',
+              'type' => 'text',
+              'size' => 'big',
+              'not null' => FALSE,
+            ),
+            'checksum_invalidations' => array(
+              'description' => 'The tag invalidation sum when this entry was saved.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+            'checksum_deletions' => array(
+              'description' => 'The tag deletion sum when this entry was saved.',
+              'type' => 'int',
+              'not null' => TRUE,
+              'default' => 0,
+            ),
+          ),
+          'indexes' => array(
+            'expire' => array('expire'),
+          ),
+          'primary key' => array('cid'),
+        );
+        db_create_table('cache_config', $spec);
+      }
+
+      require_once DRUPAL_ROOT . '/core/modules/system/system.install';
+      $tables = array(
+        'cache',
+        'cache_bootstrap',
+        'cache_block',
+        'cache_field',
+        'cache_filter',
+        'cache_form',
+        'cache_image',
+        'cache_menu',
+        'cache_page',
+        'cache_path',
+        'cache_update',
+      );
+
+      foreach ($tables as $table) {
+        system_update_8007_add_tag_column($table);
+      }
+
       // Bootstrap variables so we can update theme while preparing the update
       // process.
       drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
diff --git a/core/lib/Drupal/Core/Cache/CacheFactoryNull.php b/core/lib/Drupal/Core/Cache/CacheFactoryNull.php
new file mode 100644
index 0000000..cedcf8e
--- /dev/null
+++ b/core/lib/Drupal/Core/Cache/CacheFactoryNull.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace Drupal\Core\Cache;
+
+class CacheFactoryNull {
+  function get($bin) {
+    return new NullBackend($bin);
+  }
+}
diff --git a/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
index 8a73a20..b8bf14b 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -52,30 +52,23 @@ public function get($cid, $allow_invalid = FALSE) {
    * Implements Drupal\Core\Cache\CacheBackendInterface::getMultiple().
    */
   public function getMultiple(&$cids, $allow_invalid = FALSE) {
-    try {
-      // When serving cached pages, the overhead of using ::select() was found
-      // to add around 30% overhead to the request. Since $this->bin is a
-      // variable, this means the call to ::query() here uses a concatenated
-      // string. This is highly discouraged under any other circumstances, and
-      // is used here only due to the performance overhead we would incur
-      // otherwise. When serving an uncached page, the overhead of using
-      // ::select() is a much smaller proportion of the request.
-      $result = Database::getConnection()->query('SELECT cid, data, created, expire, serialized, tags, checksum_invalidations, checksum_deletions FROM {' . Database::getConnection()->escapeTable($this->bin) . '} WHERE cid IN (:cids)', array(':cids' => $cids));
-      $cache = array();
-      foreach ($result as $item) {
-        $item = $this->prepareItem($item, $allow_invalid);
-        if ($item) {
-          $cache[$item->cid] = $item;
-        }
+    // When serving cached pages, the overhead of using ::select() was found
+    // to add around 30% overhead to the request. Since $this->bin is a
+    // variable, this means the call to ::query() here uses a concatenated
+    // string. This is highly discouraged under any other circumstances, and
+    // is used here only due to the performance overhead we would incur
+    // otherwise. When serving an uncached page, the overhead of using
+    // ::select() is a much smaller proportion of the request.
+    $result = Database::getConnection()->query('SELECT cid, data, created, expire, serialized, tags, checksum_invalidations, checksum_deletions FROM {' . Database::getConnection()->escapeTable($this->bin) . '} WHERE cid IN (:cids)', array(':cids' => $cids));
+    $cache = array();
+    foreach ($result as $item) {
+      $item = $this->prepareItem($item, $allow_invalid);
+      if ($item) {
+        $cache[$item->cid] = $item;
       }
-      $cids = array_diff($cids, array_keys($cache));
-      return $cache;
-    }
-    catch (Exception $e) {
-      // If the database is never going to be available, cache requests should
-      // return FALSE in order to allow exception handling to occur.
-      return array();
     }
+    $cids = array_diff($cids, array_keys($cache));
+    return $cache;
   }
 
   /**
@@ -131,34 +124,29 @@ protected function prepareItem($cache, $allow_invalid) {
    * Implements Drupal\Core\Cache\CacheBackendInterface::set().
    */
   public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANENT, array $tags = array()) {
-    try {
-      $flat_tags = $this->flattenTags($tags);
-      $checksum = $this->checksumTags($flat_tags);
-      $fields = array(
-        'serialized' => 0,
-        'created' => REQUEST_TIME,
-        'expire' => $expire,
-        'tags' => implode(' ', $flat_tags),
-        'checksum_invalidations' => $checksum['invalidations'],
-        'checksum_deletions' => $checksum['deletions'],
-      );
-      if (!is_string($data)) {
-        $fields['data'] = serialize($data);
-        $fields['serialized'] = 1;
-      }
-      else {
-        $fields['data'] = $data;
-        $fields['serialized'] = 0;
-      }
-
-      Database::getConnection()->merge($this->bin)
-        ->key(array('cid' => $cid))
-        ->fields($fields)
-        ->execute();
+    $flat_tags = $this->flattenTags($tags);
+    $checksum = $this->checksumTags($flat_tags);
+    $fields = array(
+      'serialized' => 0,
+      'created' => REQUEST_TIME,
+      'expire' => $expire,
+      'tags' => implode(' ', $flat_tags),
+      'checksum_invalidations' => $checksum['invalidations'],
+      'checksum_deletions' => $checksum['deletions'],
+    );
+    if (!is_string($data)) {
+      $fields['data'] = serialize($data);
+      $fields['serialized'] = 1;
     }
-    catch (Exception $e) {
-      // The database may not be available, so we'll ignore cache_set requests.
+    else {
+      $fields['data'] = $data;
+      $fields['serialized'] = 0;
     }
+
+    Database::getConnection()->merge($this->bin)
+      ->key(array('cid' => $cid))
+      ->fields($fields)
+      ->execute();
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Cache/InstallBackend.php b/core/lib/Drupal/Core/Cache/InstallBackend.php
deleted file mode 100644
index 91d0249..0000000
--- a/core/lib/Drupal/Core/Cache/InstallBackend.php
+++ /dev/null
@@ -1,187 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\Cache\InstallBackend.
- */
-
-namespace Drupal\Core\Cache;
-
-use Exception;
-
-/**
- * Defines a stub cache implementation to be used during installation.
- *
- * The stub implementation is needed when database access is not yet available.
- * Because Drupal's caching system never requires that cached data be present,
- * these stub functions can short-circuit the process and sidestep the need for
- * any persistent storage. Obviously, using this cache implementation during
- * normal operations would have a negative impact on performance.
- *
- * If there is a database cache, this backend will attempt to clear it whenever
- * possible. The reason for doing this is that the database cache can accumulate
- * data during installation due to any full bootstraps that may occur at the
- * same time (for example, Ajax requests triggered by the installer). If we
- * didn't try to clear it whenever one of the delete function are called, the
- * data in the cache would become stale; for example, the installer sometimes
- * calls variable_set(), which updates the {variable} table and then clears the
- * cache to make sure that the next page request picks up the new value.
- * Not actually clearing the cache here therefore leads old variables to be
- * loaded on the first page requests after installation, which can cause
- * subtle bugs, some of which would not be fixed unless the site
- * administrator cleared the cache manually.
- */
-class InstallBackend extends DatabaseBackend {
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::get().
-   */
-  public function get($cid, $allow_invalid = FALSE) {
-    return FALSE;
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::getMultiple().
-   */
-  public function getMultiple(&$cids, $allow_invalid = FALSE) {
-    return array();
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::set().
-   */
-  public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANENT, array $tags = array()) {}
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::delete().
-   */
-  public function delete($cid) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::delete($cid);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::deleteMultiple().
-   */
-  public function deleteMultiple(array $cids) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::deleteMultiple($cids);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::deleteAll().
-   */
-  public function deleteAll() {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::deleteAll();
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::deleteExpired().
-   */
-  public function deleteExpired() {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::deleteExpired();
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::deleteTags().
-   */
-  public function deleteTags(array $tags) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::deleteTags($tags);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::invalidate().
-   */
-  public function invalidate($cid) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::invalidate($cid);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::invalidateMultiple().
-   */
-  public function invalidateMultiple(array $cids) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::invalidateMultiple($cids);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::invalidateTags().
-   */
-  public function invalidateTags(array $tags) {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::invalidateTags($tags);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Implements Drupal\Core\Cache\CacheBackendInterface::invalidateAll().
-   */
-  public function invalidateAll() {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::invalidateAll($tags);
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::garbageCollection().
-   */
-  public function garbageCollection() {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        parent::garbageCollection();
-      }
-    }
-    catch (Exception $e) {}
-  }
-
-  /**
-   * Overrides Drupal\Core\Cache\DatabaseBackend::isEmpty().
-   */
-  public function isEmpty() {
-    try {
-      if (class_exists('Drupal\Core\Database\Database')) {
-        return parent::isEmpty();
-      }
-    }
-    catch (Exception $e) {}
-    return TRUE;
-  }
-}
diff --git a/core/modules/system/lib/Drupal/system/Tests/Cache/InstallTest.php b/core/modules/system/lib/Drupal/system/Tests/Cache/InstallTest.php
deleted file mode 100644
index 65cb303..0000000
--- a/core/modules/system/lib/Drupal/system/Tests/Cache/InstallTest.php
+++ /dev/null
@@ -1,119 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\system\Tests\Cache\InstallTest.
- */
-
-namespace Drupal\system\Tests\Cache;
-
-use Drupal\Core\Cache\DatabaseBackend;
-use Drupal\Core\Cache\InstallBackend;
-use Exception;
-
-/**
- * Tests the behavior of the cache backend used for installing Drupal.
- */
-class InstallTest extends CacheTestBase {
-
-  /**
-   * Modules to enable.
-   *
-   * @var array
-   */
-  public static $modules = array('cache_test');
-
-  protected $profile = 'testing';
-
-  public static function getInfo() {
-    return array(
-      'name' => 'Cache install test',
-      'description' => 'Confirm that the cache backend used for installing Drupal works correctly.',
-      'group' => 'Cache',
-    );
-  }
-
-  /**
-   * Tests the behavior of the cache backend used for installing Drupal.
-   *
-   * While Drupal is being installed, the cache system must deal with the fact
-   * that the database is not initially available, and, after it is available,
-   * the fact that other requests that take place while Drupal is being
-   * installed (for example, Ajax requests triggered via the installer's user
-   * interface) may cache data in the database, which needs to be cleared when
-   * the installer makes changes that would result in it becoming stale.
-   *
-   * We cannot test this process directly, so instead we test it by switching
-   * between the normal database cache (Drupal\Core\Cache\DatabaseBackend) and
-   * the installer cache (Drupal\Core\Cache\InstallBackend) while setting and
-   * clearing various items in the cache.
-   */
-  function testCacheInstall() {
-    $database_cache = new DatabaseBackend('test');
-    $install_cache = new InstallBackend('test');
-
-    // Store an item in the database cache, and confirm that the installer's
-    // cache backend recognizes that the cache is not empty.
-    $database_cache->set('cache_one', 'One');
-    $this->assertFalse($install_cache->isEmpty());
-    $database_cache->delete('cache_one');
-    $this->assertTrue($install_cache->isEmpty());
-
-    // Store an item in the database cache, then use the installer's cache
-    // backend to delete it. Afterwards, confirm that it is no longer in the
-    // database cache.
-    $database_cache->set('cache_one', 'One');
-    $this->assertEqual($database_cache->get('cache_one')->data, 'One');
-    $install_cache->delete('cache_one');
-    $this->assertFalse($database_cache->get('cache_one'));
-
-    // Store multiple items in the database cache, then use the installer's
-    // cache backend to delete them. Afterwards, confirm that they are no
-    // longer in the database cache.
-    $database_cache->set('cache_one', 'One');
-    $database_cache->set('cache_two', 'Two');
-    $this->assertEqual($database_cache->get('cache_one')->data, 'One');
-    $this->assertEqual($database_cache->get('cache_two')->data, 'Two');
-    $install_cache->deleteMultiple(array('cache_one', 'cache_two'));
-    $this->assertFalse($database_cache->get('cache_one'));
-    $this->assertFalse($database_cache->get('cache_two'));
-
-    // Store multiple items in the database cache, then use the installer's
-    // cache backend to flush the cache. Afterwards, confirm that they are no
-    // longer in the database cache.
-    $database_cache->set('cache_one', 'One');
-    $database_cache->set('cache_two', 'Two');
-    $this->assertEqual($database_cache->get('cache_one')->data, 'One');
-    $this->assertEqual($database_cache->get('cache_two')->data, 'Two');
-    $install_cache->deleteAll();
-    $this->assertFalse($database_cache->get('cache_one'));
-    $this->assertFalse($database_cache->get('cache_two'));
-
-    // Invalidate a tag using the installer cache, then check that the
-    // invalidation was recorded correctly in the database.
-    $install_cache->invalidateTags(array('tag'));
-    $invalidations = db_query("SELECT invalidations FROM {cache_tags} WHERE tag = 'tag'")->fetchField();
-    $this->assertEqual($invalidations, 1);
-
-    // For each cache clearing event that we tried above, try it again after
-    // dropping the {cache_test} table. This simulates the early stages of the
-    // installer (when the database cache tables won't be available yet) and
-    // thereby confirms that the installer's cache backend does not produce
-    // errors if the installer ever calls any code early on that tries to clear
-    // items from the cache.
-    db_drop_table('cache_test');
-    try {
-      $install_cache->isEmpty();
-      $install_cache->delete('cache_one');
-      $install_cache->deleteMultiple(array('cache_one', 'cache_two'));
-      $install_cache->deleteAll();
-      $install_cache->deleteExpired();
-      $install_cache->garbageCollection();
-      $install_cache->invalidateTags(array('tag'));
-      $this->pass("The installer's cache backend can be used even when the cache database tables are unavailable.");
-    }
-    catch (Exception $e) {
-      $this->fail("The installer's cache backend can be used even when the cache database tables are unavailable.");
-    }
-  }
-}
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 33df8c2..87997db 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1608,66 +1608,7 @@ function system_update_8002() {
  * Creates {cache_config} cache table for the new configuration system.
  */
 function system_update_8003() {
-  $spec = array(
-    'description' =>  'Cache table for configuration data.',
-    'fields' => array(
-      'cid' => array(
-        'description' => 'Primary Key: Unique cache ID.',
-        'type' => 'varchar',
-        'length' => 255,
-        'not null' => TRUE,
-        'default' => '',
-      ),
-      'data' => array(
-        'description' => 'A collection of data to cache.',
-        'type' => 'blob',
-        'not null' => FALSE,
-        'size' => 'big',
-      ),
-      'expire' => array(
-        'description' => 'A Unix timestamp indicating when the cache entry should expire, or 0 for never.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-      'created' => array(
-        'description' => 'A Unix timestamp indicating when the cache entry was created.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-      'serialized' => array(
-        'description' => 'A flag to indicate whether content is serialized (1) or not (0).',
-        'type' => 'int',
-        'size' => 'small',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-      'tags' => array(
-        'description' => 'Space-separated list of cache tags for this entry.',
-        'type' => 'text',
-        'size' => 'big',
-        'not null' => FALSE,
-      ),
-      'checksum_invalidations' => array(
-        'description' => 'The tag invalidation sum when this entry was saved.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-      'checksum_deletions' => array(
-        'description' => 'The tag deletion sum when this entry was saved.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-    ),
-    'indexes' => array(
-      'expire' => array('expire'),
-    ),
-    'primary key' => array('cid'),
-  );
-  db_create_table('cache_config', $spec);
+  // Moved to update_prepare_d8_bootstrap.
 }
 
 /**
@@ -1715,32 +1656,7 @@ function system_update_8005() {
  * Adds the {cache_tags} table.
  */
 function system_update_8006() {
-  $table = array(
-    'description' => 'Cache table for tracking cache tags related to the cache bin.',
-    'fields' => array(
-      'tag' => array(
-        'description' => 'Namespace-prefixed tag string.',
-        'type' => 'varchar',
-        'length' => 255,
-        'not null' => TRUE,
-        'default' => '',
-      ),
-      'invalidations' => array(
-        'description' => 'Number incremented when the tag is invalidated.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-      'deletions' => array(
-        'description' => 'Number incremented when the tag is deleted.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ),
-    ),
-    'primary key' => array('tag'),
-  );
-  db_create_table('cache_tags', $table);
+  // Moved to update_prepare_d8_bootstrap.
 }
 
 /**
@@ -1750,7 +1666,7 @@ function system_update_8006() {
  *   Name of the cache table.
  */
 function system_update_8007_add_tag_column($table) {
-  if (db_table_exists($table)) {
+  if (db_table_exists($table) && !db_field_exists($table, 'tags')) {
     db_add_field($table, 'tags', array(
       'description' => 'Space-separated list of cache tags for this entry.',
       'type' => 'text',
@@ -1776,23 +1692,7 @@ function system_update_8007_add_tag_column($table) {
  * Modifies existing cache tables, adding support for cache tags.
  */
 function system_update_8007() {
-  $tables = array(
-    'cache',
-    'cache_bootstrap',
-    'cache_form',
-    'cache_page',
-    'cache_menu',
-    'cache_path',
-    'cache_filter',
-    'cache_image',
-    'cache_update',
-    'cache_block',
-    'cache_field',
-  );
-
-  foreach ($tables as $table) {
-    system_update_8007_add_tag_column($table);
-  }
+  // Moved to update_prepare_d8_bootstrap.
 }
 
 /**