Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.255.2.37
diff -u -p -r1.255.2.37 menu.inc
--- includes/menu.inc	4 Nov 2010 09:58:34 -0000	1.255.2.37
+++ includes/menu.inc	20 Nov 2010 15:24:12 -0000
@@ -1738,6 +1738,180 @@ function menu_router_build($reset = FALS
     drupal_alter('menu', $callbacks);
     $menu = _menu_router_build($callbacks);
     _menu_router_cache($menu);
+
+    // We no longer need the callbacks.
+    unset($callbacks, $router_items, $module, $path);
+
+    // Get the old menu from the cache if we can, otherwise assume an initial build
+    // and empty menu_router.
+    $menu_old = array();
+    if ($data = cache_get('menu_router_build_old_menu')) {
+      $menu_old = $data->data;
+
+      // Unset $data to save on memory usage.
+      unset($data);
+
+      // Empty the cache immediatly in case there is an error whilst processing changes
+      // so we don't get left in a indeterminant state.
+      cache_clear_all('menu_router_build_old_rows', 'cache');
+    }
+    else {
+      db_query('TRUNCATE TABLE {menu_router}');
+    }
+
+    // Cacluate the changes.
+    $changes_insert = array();
+    $changes_update = array();
+    $changes_delete = array();
+    foreach (array_keys($menu) as $path) {
+      $row_new = $menu[$path];
+
+      // If only a new path, then do an insert.
+      if (!isset($menu_old[$path])) {
+        $changes_insert[$path] = $row_new;
+      }
+      else {
+        // Get a sepcific subset of changes for this row.
+        $row_changes = array();
+        foreach ($row_new as $key => $value) {
+          if ($value != $menu_old[$path][$key]) {
+            $row_changes[$key] = $value;
+          }
+        }
+
+        // If nothing changed, do nothing.
+        if (!empty($row_changes)) {
+          $changes_update[$path] = $row_changes;
+        }
+
+        // Make sure this row is not triggered for deletion.
+        unset($menu_old[$path]);
+      }
+    }
+
+    // Delete remaining rows.
+    foreach ($menu_old as $path => $row_old) {
+      $changes_delete[$path] = $path;
+    }
+
+    // We no longer need $menu_old or other items.
+    unset($menu_old, $path, $row_new, $row_changes, $row_old);
+
+    // Set up a database map.
+    $db_map = array(
+      'path' => 'path',
+      'load_functions' => 'load_functions',
+      'to_arg_functions' => 'to_arg_functions',
+      'access callback' => 'access_callback',
+      'access arguments' => 'access_arguments',
+      'page callback' => 'page_callback',
+      'page arguments' => 'page_arguments',
+      '_fit' => 'fit',
+      '_number_parts' => 'number_parts',
+      'tab_parent' => 'tab_parent',
+      'tab_root' => 'tab_root',
+      'title' => 'title',
+      'title callback' => 'title_callback',
+      'title arguments' => 'title_arguments',
+      'type' => 'type',
+      'block callback' => 'block_callback',
+      'description' => 'description',
+      'position' => 'position',
+      'weight' => 'weight',
+      'include file' => 'file',
+    );
+
+    // Perform the inserts.
+    if (!empty($changes_insert)) {
+      // The SQL is always the same, only the values change.
+      $menu_fields = array_keys(current($changes_insert));
+
+      // Map fields from the router build to the db equivelant.
+      $fields = array();
+      $value_fields = array();
+      foreach ($menu_fields as $mfield) {
+        if (isset($db_map[$mfield])) {
+          $fields[] = $db_map[$mfield];
+          $value_fields[] = $mfield;
+        }
+      }
+
+      $tokens = db_placeholders($fields, 'varchar');
+      $fields = implode(', ', $fields);
+      $sql = "INSERT INTO {menu_router} ($fields) VALUES ($tokens)";
+
+      foreach (array_keys($changes_insert) as $key) {
+        // Map values from the router build the db equivelant.
+        $values = array();
+        foreach ($value_fields as $mfield) {
+          $value = $changes_insert[$key][$mfield];
+          if ($mfield == 'access arguments' || $mfield == 'page arguments') {
+            $values[] = serialize($value);
+          }
+          elseif ($mfield == 'title arguments') {
+            $values[] = $value ? serialize($value) : '';
+          }
+          else {
+            $values[] = $value;
+          }
+        }
+
+        db_query($sql, $values);
+      }
+    }
+
+    // We no longer need the insert changes.
+    unset($changes_insert, $menu_fields, $fields, $value_fields, $tokens, $sql, $key, $mfield, $value, $values);
+
+    // Perform the updates.
+    foreach (array_keys($changes_update) as $path) {
+      $row_changes = $changes_update[$path];
+
+      // The path should not change. (It's our key).
+      unset($row_changes['path']);
+
+      $set = $args = array();
+      foreach ($row_changes as $mfield => $value) {
+        if (isset($db_map[$mfield])) {
+          $set[] = $db_map[$mfield] ." = '%s'";
+          if ($mfield == 'access arguments' || $mfield == 'page arguments') {
+            $args[] = serialize($value);
+          }
+          elseif ($mfield == 'title arguments') {
+            $args[] = $value ? serialize($value) : '';
+          }
+          else {
+            $args[] = $value;
+          }
+        }
+      }
+
+      if (!empty($set)) {
+        $set = implode(', ', $set);
+        $sql = "UPDATE {menu_router} SET $set WHERE path = '%s'";
+
+        $args[] = $path;
+        db_query($sql, $args);
+      }
+    }
+
+    // We no longer need the update changes.
+    unset($changes_update, $row_changes, $path, $set, $args, $db_map, $mfield, $value, $sql);
+
+    // Perform the delets.
+    $sql = "DELETE FROM {menu_router} WHERE path = '%s'";
+    foreach ($changes_delete as $path) {
+      db_query($sql, $path);
+    }
+
+    // We no longer need the delete changes.
+    unset($changes_delete, $path, $sql);
+
+    // Store the new rows in a cache for use as old rows on next rebuild.
+    // We can't store this in cache_menu, as this would get wiped almost instantlty
+    // due to a call to menu_cache_clear_all() right after the router build,
+    // meaning we could never actually use it, so store in cache instead.
+    cache_set('menu_router_build_old_menu', $menu);
   }
   return $menu;
 }
@@ -2358,8 +2532,7 @@ function _menu_router_build($callbacks) 
     watchdog('php', 'Menu router rebuild failed - some paths may not work correctly.', array(), WATCHDOG_ERROR);
     return array();
   }
-  // Delete the existing router since we have some data to replace it.
-  db_query('DELETE FROM {menu_router}');
+
   // Apply inheritance rules.
   foreach ($menu as $path => $v) {
     $item = &$menu[$path];
@@ -2439,24 +2612,6 @@ function _menu_router_build($callbacks) 
       $file_path = $item['file path'] ? $item['file path'] : drupal_get_path('module', $item['module']);
       $item['include file'] = $file_path .'/'. $item['file'];
     }
-
-    $title_arguments = $item['title arguments'] ? serialize($item['title arguments']) : '';
-    db_query("INSERT INTO {menu_router}
-      (path, load_functions, to_arg_functions, access_callback,
-      access_arguments, page_callback, page_arguments, fit,
-      number_parts, tab_parent, tab_root,
-      title, title_callback, title_arguments,
-      type, block_callback, description, position, weight, file)
-      VALUES ('%s', '%s', '%s', '%s',
-      '%s', '%s', '%s', %d,
-      %d, '%s', '%s',
-      '%s', '%s', '%s',
-      %d, '%s', '%s', '%s', %d, '%s')",
-      $path, $item['load_functions'], $item['to_arg_functions'], $item['access callback'],
-      serialize($item['access arguments']), $item['page callback'], serialize($item['page arguments']), $item['_fit'],
-      $item['_number_parts'], $item['tab_parent'], $item['tab_root'],
-      $item['title'], $item['title callback'], $title_arguments,
-      $item['type'], $item['block callback'], $item['description'], $item['position'], $item['weight'], $item['include file']);
   }
   // Sort the masks so they are in order of descending fit, and store them.
   $masks = array_keys($masks);