Issue #2494221 by david_garcia, dagmar: Slow Log/Watchdog clear when there are lots of data

CHANGELOG.txt

@@ -3,6 +3,7 @@ Drupal 7.54, xxxx-xx-xx (development version)
 -----------------------
 - Modules are now able to define theme engines.
 - Numerous bug fixes.
+- Numerous performance improvements.
 - Numerous API documentation improvements.
 - Logging of searches can now be disabled.
 - Added menu tree render structure to (pre-)process hooks for theme_menu_tree().

modules/dblog/dblog.admin.inc

@@ -420,6 +420,6 @@ function dblog_clear_log_form($form) {
  */
 function dblog_clear_log_submit() {
   $_SESSION['dblog_overview_filter'] = array();
-  db_delete('watchdog')->execute();
+  db_truncate('watchdog')->execute();
   drupal_set_message(t('Database log cleared.'));
 }