fixes #1392 improve performances to find related albums

* new conf setting related_albums_maximum_items_to_compute (1000 by default). Beyond this number of photos in current set, do not try to find related albums.

* new conf setting related_albums_display_limit : only display the heaviest (most related) albums.

include/config_default.inc.php

@@ -643,6 +643,19 @@ $conf['tags_default_display_mode'] = 'cloud';
 // tag_letters_column_number: how many columns to display tags by letter
 $conf['tag_letters_column_number'] = 4;
 
+// +-----------------------------------------------------------------------+
+// | Related albums                                                        |
+// +-----------------------------------------------------------------------+
+
+// beyond this limit, do not try to find related albums. If there are too
+// many items, the SQL query will be slow and the results irrelevant,
+// because showing too many related albums.
+$conf['related_albums_maximum_items_to_compute'] = 1000;
+
+// once found the related albums, how many to show in the menubar? We take
+// the heaviest (with more relations).
+$conf['related_albums_display_limit'] = 20;
+
 // +-----------------------------------------------------------------------+
 // | Notification by mail                                                  |
 // +-----------------------------------------------------------------------+

include/functions_category.inc.php

@@ -718,9 +718,9 @@ SELECT
 
 function get_related_categories_menu($items, $excluded_cat_ids=array())
 {
-  global $page;
+  global $page, $conf;
 
-  $common_cats = get_common_categories($items, null, $excluded_cat_ids);
+  $common_cats = get_common_categories($items, $conf['related_albums_display_limit'], $excluded_cat_ids);
   // echo '<pre>'; print_r($common_cats); echo '</pre>';
 
   if (count($common_cats) == 0)

include/menubar.inc.php

@@ -104,7 +104,12 @@ function initialize_menu()
 //------------------------------------------------------------ related categories
   $block = $menu->get_block('mbRelatedCategories');
 
-  if ($block != null and !empty($page['items']))
+  if (
+    isset($page['items'])
+    and count($page['items']) < $conf['related_albums_maximum_items_to_compute']
+    and $block != null
+    and !empty($page['items'])
+  )
   {
     $exclude_cat_ids = array();
     if (isset($page['category']))