added persistent cache for some slow queries in feed notification (even if not important to be fast on RSS feed, it might slow down galleries that are very large and actively used)

git-svn-id: http://piwigo.org/svn/trunk@28560 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions_notification.inc.php

@@ -441,8 +441,13 @@ function news($start=null, $end=null, $exclude_img_cats=false, $add_url=false)
  */
 function get_recent_post_dates($max_dates, $max_elements, $max_cats)
 {
-  global $conf, $user;
+  global $conf, $user, $persistent_cache;
 
+  $cache_key = $persistent_cache->make_key('recent_posts'.$user['id'].$user['cache_update_time'].$max_dates.$max_elements.$max_cats);
+  if ($persistent_cache->get($cache_key, $cached))
+  {
+    return $cached;
+  }
   $where_sql = get_std_sql_where_restrict_filter('WHERE', 'i.id', true);
 
   $query = '
@@ -493,6 +498,7 @@ SELECT
     }
   }
 
+  $persistent_cache->set($cache_key, $dates);
   return $dates;
 }