diff --git a/core/lib/Drupal/Core/Database/Query/Merge.php b/core/lib/Drupal/Core/Database/Query/Merge.php
index 3d7564a..ee0406a 100644
--- a/core/lib/Drupal/Core/Database/Query/Merge.php
+++ b/core/lib/Drupal/Core/Database/Query/Merge.php
@@ -11,8 +11,6 @@
 use Drupal\Core\Database\Connection;
 use Drupal\Core\Database\IntegrityConstraintViolationException;
 
-use Exception;
-
 /**
  * General class for an abstracted MERGE query operation.
  *
@@ -405,54 +403,42 @@ public function __toString() {
   }
 
   public function execute() {
-    // Wrap multiple queries in a transaction, if the database supports it.
-    $transaction = $this->connection->startTransaction();
-    try {
-      if (!count($this->condition)) {
-        throw new InvalidMergeQueryException(t('Invalid merge query: no conditions'));
-      }
-      $select = $this->connection->select($this->conditionTable)
-        ->condition($this->condition)
-        ->forUpdate();
-      $select->addExpression('1');
-      if (!$select->execute()->fetchField()) {
-        try {
-          $insert = $this->connection->insert($this->table)->fields($this->insertFields);
-          if ($this->defaultFields) {
-            $insert->useDefaults($this->defaultFields);
-          }
-          $insert->execute();
-          return self::STATUS_INSERT;
-        }
-        catch (IntegrityConstraintViolationException $e) {
-          // The insert query failed, maybe it's because a racing insert query
-          // beat us in inserting the same row. Retry the select query, if it
-          // returns a row, ignore the error and continue with the update
-          // query below.
-          if (!$select->execute()->fetchField()) {
-            throw $e;
-          }
+    if (!count($this->condition)) {
+      throw new InvalidMergeQueryException(t('Invalid merge query: no conditions'));
+    }
+    $select = $this->connection->select($this->conditionTable)
+      ->condition($this->condition);
+    $select->addExpression('1');
+    if (!$select->execute()->fetchField()) {
+      try {
+        $insert = $this->connection->insert($this->table)->fields($this->insertFields);
+        if ($this->defaultFields) {
+          $insert->useDefaults($this->defaultFields);
         }
+        $insert->execute();
+        return self::STATUS_INSERT;
       }
-      if ($this->needsUpdate) {
-        $update = $this->connection->update($this->table)
-          ->fields($this->updateFields)
-          ->condition($this->condition);
-        if ($this->expressionFields) {
-          foreach ($this->expressionFields as $field => $data) {
-            $update->expression($field, $data['expression'], $data['arguments']);
-          }
+      catch (IntegrityConstraintViolationException $e) {
+        // The insert query failed, maybe it's because a racing insert query
+        // beat us in inserting the same row. Retry the select query, if it
+        // returns a row, ignore the error and continue with the update
+        // query below.
+        if (!$select->execute()->fetchField()) {
+          throw $e;
         }
-        $update->execute();
-        return self::STATUS_UPDATE;
       }
     }
-    catch (Exception $e) {
-      // Something really wrong happened here, bubble up the exception to the
-      // caller.
-      $transaction->rollback();
-      throw $e;
+    if ($this->needsUpdate) {
+      $update = $this->connection->update($this->table)
+        ->fields($this->updateFields)
+        ->condition($this->condition);
+      if ($this->expressionFields) {
+        foreach ($this->expressionFields as $field => $data) {
+          $update->expression($field, $data['expression'], $data['arguments']);
+        }
+      }
+      $update->execute();
+      return self::STATUS_UPDATE;
     }
-    // Transaction commits here where $transaction looses scope.
   }
 }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index ac70335..33df8c2 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1744,35 +1744,54 @@ function system_update_8006() {
 }
 
 /**
+ * Adds tags, checksum_invalidations, checksum_deletions to a cache table.
+ *
+ * @param string $table
+ *   Name of the cache table.
+ */
+function system_update_8007_add_tag_column($table) {
+  if (db_table_exists($table)) {
+    db_add_field($table, 'tags', array(
+      'description' => 'Space-separated list of cache tags for this entry.',
+      'type' => 'text',
+      'size' => 'big',
+      'not null' => FALSE,
+    ));
+    db_add_field($table, 'checksum_invalidations', array(
+      'description' => 'The tag invalidation sum when this entry was saved.',
+      'type' => 'int',
+      'not null' => TRUE,
+      'default' => 0,
+    ));
+    db_add_field($table, 'checksum_deletions', array(
+      'description' => 'The tag deletion sum when this entry was saved.',
+      'type' => 'int',
+      'not null' => TRUE,
+      'default' => 0,
+    ));
+  }
+}
+
+/**
  * Modifies existing cache tables, adding support for cache tags.
  */
 function system_update_8007() {
-  // Find all potential cache tables.
-  $tables = db_find_tables(Database::getConnection()->prefixTables('{cache}') . '%');
+  $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 $table) {
-    // Assume we have a valid cache table if there is both 'cid' and 'data'
-    // columns.
-    if (db_field_exists($table, 'cid') && db_field_exists($table, 'data') && !db_field_exists($table, 'tags')) {
-      db_add_field($table, 'tags', array(
-        'description' => 'Space-separated list of cache tags for this entry.',
-        'type' => 'text',
-        'size' => 'big',
-        'not null' => FALSE,
-      ));
-      db_add_field($table, 'checksum_invalidations', array(
-        'description' => 'The tag invalidation sum when this entry was saved.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ));
-      db_add_field($table, 'checksum_deletions', array(
-        'description' => 'The tag deletion sum when this entry was saved.',
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-      ));
-    }
+    system_update_8007_add_tag_column($table);
   }
 }