http://drupal.org/node/557806

From: andrew morton <graveltech@gmail.com>

Cache the toolbar per-user
---

 modules/toolbar/toolbar.module |   17 +++++++++++++++--
 1 files changed, 15 insertions(+), 2 deletions(-)


diff --git modules/toolbar/toolbar.module modules/toolbar/toolbar.module
index 0ab6f87..df58af3 100644
--- modules/toolbar/toolbar.module
+++ modules/toolbar/toolbar.module
@@ -32,7 +32,7 @@ function toolbar_theme($existing, $type, $theme, $path) {
 
 /**
  * Implement hook_page_alter().
- * 
+ *
  * Add admin toolbar to the page_top region automatically.
  */
 function toolbar_page_alter(&$page) {
@@ -58,6 +58,17 @@ function toolbar_preprocess_page(&$vars) {
 function toolbar_build() {
   global $user;
 
+  // When building the toolbar we need to fetch the entire admin menu tree and
+  // check the user's access to each menu link, an expensive process. To avoid
+  // this the toolbar is cached on a per-user basis because the access callbacks
+  // can use an arbitrary criteria unrelated to roles or permissions. Since the
+  // toolbar is generally only accessible to a limited number of users, and is
+  // rendered on every page, it should still be more efficient than building it
+  // each time.
+  if ($cached = cache_get('toolbar:user:' . $user->uid, 'cache_block')) {
+    return $cached->data;
+  }
+
   $module_path = drupal_get_path('module', 'toolbar');
   $build = array(
     '#theme' => 'toolbar',
@@ -104,6 +115,8 @@ function toolbar_build() {
     '#attributes' => array('id' => 'toolbar-shortcuts'),
   );
 
+  cache_set('toolbar:user:' . $user->uid, $build, 'cache_block');
+
   return $build;
 }
 
@@ -162,7 +175,7 @@ function toolbar_menu_navigation_links($tree) {
 /**
  * Checks whether an item is in the active trail.
  *
- * Useful when using a menu generated by menu_tree_all_data() which does 
+ * Useful when using a menu generated by menu_tree_all_data() which does
  * not set the 'in_active_trail' flag on items.
  *
  * @todo